Donor specific antibodies made easy

Donor specific Antibodies (DSA) are one of the established biomarkers for predicting antibody mediated rejection (ABMR). This blog is a short synopsis on DSA and their complex characteristics  in kidney transplantation.

DSA may be preformed (before transplantation) or de-novo (developing after transplantation). Preformed DSA can lead to hyperacute/early ABMR and graft loss. De-novo DSA can lead to late ABMR and poor graft prognosis. But DSA need not always be pathogenic- often they may act in a ‘benign’ fashion, with stable graft function.

Sensitization
The main sensitizing events include organ transplant itself pregnancies and blood transfusions. It is important for the clinician to take the history of shared children with a partner who is a potential live donor. Sensitization is generally represented as the % panel reactive antibody (PRA), the proportion of a representative population that the recipient has anti-HLA antibodies to. This also estimates the likelihood of a positive cross match to potential donors.

DSA identification
We have come a long way from the less sensitive complement based cytotoxic assays and ELISA to the newer and more sensitive multiplexed particle based flow cytometry (e.g. Luminex, see image). The newest kid on the block of sensitive testing for DSA is next generation sequencing (NGS). Single bead antigens assessed on a Luminex platform can identify the precise antibody present. This information is used in identifying preformed antibodies against a potential donor on a virtual cross match (so called because single antigen beads are added to recipient serum, without donor cells being involved). When ABMR is suspected, the presence of de-novo DSA or rising titers of pre-existing DSA contributes to the diagnosis.

DSA Pathogenesis
De-novo DSA can develop in 30% of transplant recipients who were previously not sensitized. De-novo DSA mainly develop against HLA Class II antigens (often DQ). The risk factors for de-novo DSA formation include:

• High HLA mismatches (especially DQ).
• Inadequate/non adherence to immunosuppression.
• Graft inflammation which leads to increased immunogenicity  (viral infections like CMV, cellular rejection episodes or ischemic injury).

DSA cause graft injury via complement activation, antibody dependent cellular cytotoxicity, and direct injury of the endothelium via VEGF, fibroblast growth factor upregulation and ligand binding. These latter two non complement mediated mechanisms may explain the c4d negative ABMR.

Importance of DSA class & IgG Subclass
DSA target specific epitopes in the polymorphic regions of the HLA antigens (see NephMadness for more on epitopes/eplets).
HLA Class I: A,B,C antigens; present on all nucleated cells, one alpha chain and a beta2-microglobulin; epitopes located on the polymorphic alpha chain.
HLA Class II: DR, DQ, DP; present on all antigen-presenting cells, one alpha & 1 beta chain; both chains are polymorphic.

IgG1	IgG2	IgG3	IgG4
Complement binding Most abundant	Weakly complement binding	Complement binding (best) Mainly associated with acute ABMR	Does not bind complement at all Biomarker of mature alloresponse and chronic graft injury

Class I and Class II DSA
Class I antibodies are usually of IgG1 or IgG3 subclass so are usually complement binding. They are unusally associated with acute ABMR and graft loss. Class II antibodies are usually IgG2/4 subclass and are usually detected late and are not complement binding. Usually quite persistent and associated with chronic injury.

What are complement binding DSA?

Complement binding DSA, as judged by C1q fixing on single bead assays, is associated with a worse allograft prognosis, with some evidence that C3d fixation may also be important (previous RFN post here). This is a controversial area as complement fixation may be induced by concentrating DSA and lost by dilution so antibody strength may explain at least of this association. Why might this be important? C1q represents the early part of complement activation whereas C3d and C4d are more downstream mediators of complement activation

DSA Strength
Usually expressed as the Mean Fluorescence Intensity (MFI) on the solid phase (single bead) assay. There is no standardisation currently and each transplant center develops their own cut-offs. Important points to consider regarding DSA strength (see NephMadness for more): (i) Prozone effect: False negative or low titers may occur despite high levels of antibody in the presence of inhibitors (serial dilutions help mitigate prozone effect). (ii) DSA against shared epitopes may be diluted across the beads giving lower individual MFI.

Relationship between DSA and C4d deposition in the kidney
C4d is the degradation product of the classic complement pathway. It binds covalently to the endothelial basement membrane. Positive C4d staining in peritubular capillaries serves as an immunological foot print of ABMR – seen as a linear pattern best seen in frozen tissue section. It is important to note that not all ABMR will be C4d positive and that isolated C4d positivity may not portend a bad prognosis (graft accommodation in ABO incompatible transplantation is a well known example).

Post by Rajeeva Parthasarathy

Third Midwest Nephrology and Transplant Symposium

Please check out the link for full details. Includes an ultrasound for nephrologists workshop!

The Revolution of Medical Learning - Exploring Novel Teaching Tools…

Textbooks and formal lectures were previously considered the main sources to build a solid medical knowledge. However, the advancements of technology have transformed our learning process. Nowadays, students, residents and fellows learn from a combination of resources including Internet, Uptodate, webcasts, podcasts, blogs and apps in addition to formal teaching. 

One of the limitations of this is that learning became fragmented… I have personally experienced this fact as an Attending since fellows would learn very well certain topics in transplantation such as treatment of antibody-mediated rejection though would lack basic concepts about histocompatibility at the end of their fellowship. They were interested in learning more about anti-HLA testing though did not have the time to visit the lab or to read about it, in particular since most books go into to excessive details for their learning needs. 

Ultrasound is another area where fellows really ought to learn more during their fellowship, since I am confident that performing a bedside ultrasound can significantly improve patient care by identifying earlier abnormalities such as an obstruction or a lack of blood flow in kidney grafts. Ultrasound books made by radiologists are also over detailed for the fellow and are rarely used in practice. 

Finally, learning to assess kidney transplant biopsies and nuances of the diagnoses of various conditions is critical for the appropriate management of patients. Most centers lack a formal teaching of how to consistently approach a kidney biopsy. Helmut Rennke and Vanesa Bijol, two fabulous renal pathologist at the BWH, were critical for my learning on this topic but there is no fellow-oriented resource to quickly overview this subject other than renal pathology books. 

 To overcome the above limitations, I have been working for the past 6 years in an interactive transplant learning tool that contains more than 300 original figures/illustrations, questions, key-points and videos to consolidate all aspects of transplantation in one place. Helmut and Vanesa have provided me with slides from all kidney transplant patients that I have attended on, allowing me to share individual cases with beautiful biopsy findings. 

It was a lot of work since I decided to do all by myself, including illustrations, collection of radiology images, videos, graphs, questions,… The goal was really to have a book with a consistent approach to topics and similar style through out. This would be impossible if I had invited multiple contributors… Videos were elaborated to explain difficult topics such as anti-HLA assays, and problem-based cases describe the thought processes, differential diagnosis and management of common conditions affecting kidney transplant recipients. Lastly, questions and review key-points on every chapter will test the reader’s knowledge and hyperklinks will allow direct access with one-click to key references on Pubmed. The end-product was just made available online two weeks ago. 

I hope students, residents and fellows would enjoy the format and really get the most learning possible while seeing transplant patients. Our beta testing last year with BWH fellows was excellent! 

Hopefully you will also enjoy it...

 Have fun! 

Leo Riella

PS1. Read more about it the iBook here

PS2. To download the iBook,  an iPad, iPhone 6 or Mac computer is required. 

Is there a benefit in pre-transplant weight loss? #NephMadness

To complement the NephMadness Nutrition in Nephrology obesity match-ups, we thought a post on pre-transplant weight loss was timely. According to a recent report published in JAMA, more than one third of the US population are obese (BMI>30) with an estimated medical annual cost of $147million in 2008. Obesity causes heart disease, stroke, type 2 diabetes mellitus and certain types of cancer. According to a recent policy statement of ASCO, obesity is predicted to overtake tobacco as the leading modifiable cause of cancer in the United States in the near future.
In the Nephrology world, we are all aware of the survival advantage of obesity in dialysis patients with the so-called “reverse epidemiology” or “obesity paradox” (While obesity, hypertension and hyperlipidemia are indicators of high cardiovascular risk in the general population, in dialysis patients these conditions are associated with a survival advantage). This was demonstrated in several well-conducted studies (ref, ref, ref) in the United States and Europe.

But is there any survival advantage for obese patients while they are waiting for a kidney transplant? Obesity is not an absolute contraindication for transplant listing although some transplant centers do not evaluate patients with BMI >30-35 kg/m2. At our center, we recommend patients should aim for a BMI < 35kg/m2; however we have performed kidney transplants in patients with higher BMIs. Approximately 60% of kidney transplant recipients are overweight, which represents a 116% increase from 1987. But is BMI an accurate reflection of obesity in adults? The answer is no. The accuracy is limited and although a BMI cutoff of >30 kg/m2 has good specificity, it misses more than half of people with excess fat. Newer techniques to evaluate obesity include abdominal circumference, waist to hip ratio, hydrostatic weighing and body fat measuring.

There are concerns about allograft survival, weight gain after kidney transplantation and wound healing. Two retrospective analyses in obese patients undergoing kidney transplantation reported higher rates of delayed graft function, acute rejection, peri-operative complications and worse renal function with higher BMIs.
On the other hand, there is evidence that higher BMIs do not influence outcomes. A study of >164,000 patients demonstrated that low pre-transplant BMI, low pre-transplant serum creatinine (which could be due to sarcopenia), were associated with worse post-transplant outcomes. Bariatric surgery is becoming more popular prior to kidney transplantation and according to this study of USRDS data that evaluated the safety of the procedure, bariatric surgery provides substantial weight loss to kidney recipients. However, it also reported more peri-operative complications and increased mortality in comparison to patients undergoing the same procedure without kidney disease. Significant pre-transplant weight loss (>10kgs) may be a risk factor for peri-operative complications, particularly wound problems. Another study reported that weight loss during transplant listing had no effect on long term outcomes after transplantation and rapid weight loss was associated with subsequent post-transplant rapid weight gain. According to this analysis, the rate of mortality before and after transplantation is unchanged despite weight loss.

In conclusion, there is no evidence that weight loss before transplantation improves long-term outcomes following transplantation although much of the evidence is retrospective and observational in nature. The absence of significant central obesity certainly helps with wound healing and it is intuitive that a ‘healthy weight’ augers well for long term morbidity. How we measure this ‘healthy weight’ however is debatable including where BMI fits into this assessment, if at all.

Hector M. Madariaga,
SUNY Upstate Medical University

FSGS biomarker updates—suPAR, B7-1, CD40 and more…

FSGS is the most common glomerular disorder causing end-stage kidney disease in the USA with a high post-transplant recurrence rate of 20-50%. Furthermore, the treatment of post-transplant recurrent FSGS is extremely challenging. While reading a recent article on biomarkers predicting post-transplant recurrent FSGS by Delville et al. (discussed below), it seemed a good idea to cover recent advancement in FSGS research. 

 suPAR (soluble plasminogen activator receptor) 
Since the first report by Wei et al. of suPAR as a circulating permeability factor causing FSGS, there has been extensive research to elucidate its role in FSGS. Although administration of suPAR molecule to mice was initially thought to be sufficient to cause proteinuria mimicking FSGS, via activation of integrin beta 3 and derangement of actin cytoskeleton, the situation does not seem that straightforward. As Reiser et al. discussed, there are challenges to overcome: existence of different suPAR isoforms with different disease modifying effects; heterogeneity of FSGS itself, which make it complicated to interpret correlation between levels of suPAR and disease activity; involvement of suPAR in other disease process, including cardiovascular disease (KI 2014). However, suPAR remains an intriguing molecule and potential biomarker in FSGS disease process.

 B7-1 (CD80)
A case series in the NEJM from Peter Mundel’s group in the end of 2013 brought us to an excitement for personalized treatment of a subgroup of B7-1 positive FSGS patients. They found strong B7-1 stain in primary FSGS as well as post-transplant recurrent FSGS. These patients were successfully treated with abatacept (CTLA4-Ig), resulting in complete remission of proteinuria. The hypothetical pathophysiological mechanism was via direct interaction of B7-1 and integrin beta 1 causing podocyte actin cytoskeleton changes. However, it was followed by comments and larger case series (AJKD 2014) questioning specificity of the immunostaining and treatment effect of abatacept. Exploration of this costimulatory molecule in FSGS was just started and further research is needed. 

Micro RNA(s) as biomarkers for FSGS disease activity 
A group from China suggested that certain micro RNAs are associated with disease activity (level of proteinuria) and progression (Zhang et al. CJASN and AJKD 2014). Potential candidates are miR-186 (involved in cell cycle control, AKT and insulin signaling etc.) and miR-125b (involved in NFkB signaling etc.). However, their contribution to pathogenesis is not clear so far.

 Pre-transplant antibody panel (including anti-CD40) to predict post transplant recurrent FSGS
Expanding potential FSGS biomarkers is the publication by Delville et al. The authors did a beautiful translational work using human serum in protein arrays, validation of specific auto-antibodies and further experimentation using cell cultures and animals models. The authors elegantly showed that pre-transplant antibody panel, especially anti-CD40 antibody, can predict risk of post-transplant recurrent FSGS.
In more detail, they started by comparing pre-transplant sera of non-recurrent FSGS (nrFSGS) vs recurrent FSGS (rFSGS), identifying 789 autoantibodies upregulated only in rFSGS but not in nrFSGS. Then those antibodies were enriched for those Ab with antigen targets expressed in kidney (151 autoAbs) and more specifically in glomeruli (10 autoAbs). They validated the 7-antibody panel (CD40, CGB5 (chorionic gonadotropin b), PTPRO (protein tyrosine phosphatase receptor O), FAS (TNF receptor superfamily member 6), P2RY11 (P2Y purinoceptor 11), SNRPB2 (small nuclear retinoid X receptor a), and APOL2 (Apolipoprotein 2)) in rFSGS vs nrFSGS cohort, and obtained ROC AUC of 0.92. Surprisingly, anti-CD40 itself had a high ROC AUC (0.77). Then, the involvement of rFSGS-anti-CD40 IgG to enhance FSGS recurrence was confirmed in vitro—rFSGS-anti-CD40 IgG caused actin cytoskeleton derangement in podocyte cell culture—, as well as in vivo—co-injection of rFSGS-anti-CD40 IgG and suPAR molecule markedly enhanced proteinuria (in a suPAR-dependent manner), which was inhibited by CD40-blocking antibody or in CD40 knockout mice. This suggests that by checking pre-transplant anti-CD40 antibody, we may be able to identify a high risk FSGS recurrence group. To manage these patients, current options are: peritransplant plasmaphresis or rituximab. Interesting to see if CD40 antagonist or blocking antibody can play a role in preventing/treating rFSGS in the clinic...

Naoka Murakami

“Liquid Biopsy” – measuring cell-free circulating donor DNA to predict allograft rejection

Transplant physicians face the challenge to detect allograft rejection using non-sensitive biomarkers and clinical signs/symptoms. 

For kidney transplant, serum creatinine, urinalysis for proteinuria or hematuria, are so far used for screening for rejection and/or assessment of graft function. In a recent article in Sci Transl Med, De Vlaminck et al. investigated the use of cell-free circulating DNA (cfdDNA) as a marker of allograft rejection in adult heart transplants. 

Authors used shotgun sequence approach to detect donor-specific DNA fragments (SNP genotyping), and correlated the level of cfdDNA with cardiac biopsy results, the diagnostic “gold standard” for rejection. 

The idea of a “liquid biopsy” —using plasma circulating DNA fragments—as a diagnostic tool has been explored in the Oncology field, to detect early and late stage cancers. In transplant field, the presence of donor-derived DNA fragments in recipient’s plasma (or urine), called microchimerism, has been known since the end of 1990s  and using them as a measure of transplant injury has been tried. For example, Sidgel et al. used Y-specific DNA fragments as a marker in male-to-female transplants. 

 In this current article, De Vlaminck et al. further improved this approach to overcome dependency on donor-recipient pair. Authors concluded that using the cutoff value of 0.25%, cfdDNA method is as sensitive (0.58) and specific (0.87) as biopsy (0.58 and 0.96, respectively). Furthermore, cfdDNA approach was able to detect rejection as early as 5 months prior to tissue diagnosis. 

There are, of course, some limitations to overcome: 1) cfdDNA cannot differentiate ACR vs AMR, 2) cannot rule out other source of DNA fragments, such as endothelial damage without rejection 3) exhibit still substantial discordance with biopsy results. Although currently using the shotgun approach, the technique can be refined by using targeted-sequencing approach, to be less laborious process. 

Based on the same underlying principles, it is very likely that similar test would have application in kidney transplantation and potentially help to detect earlier ongoing graft injury. We will still need the biopsy though to clarify the type of injury...

Naoka Murakami

Deceased Donor Kidney Allocation 2014

In the USA in June 2013 the OPTN/UNOS Board of Directors approved amendments to the OPTN policy for deceased donor kidney allocation. These ideas have been discussed for the last 9 years and Nate wrote about some of these ideas here and posted a poll here. The central premise for the changes were outlined in a press release on the OPTN website here. The exact dates for nation wide implementation are not currently available.

Longevity-matching

This is the main and most interesting part of the new system.

Priority will be given to transplant recipients most likely to live the longest post transplant. Each recipient is given an EPTS (estimated post-transplant survival) score ranging from 1 to 100%. This score is calculated from recipient characteristics; Age, years on dialysis, presence of diabetes and prior solid organ transplant.

Here is the OPTN online EPTS calculator

Remember the EPTS score needs to be updated daily.

·      The lower percentage EPTS score the longer estimated survival.

Recipients in the top 20^th percentile will be prioritized for the best kidneys, that is kidneys with a KDPI (Kidney Donor Profile Index) of less than 20%. The KDPI is a re-working of the Kidney Donor Risk Index, which is a risk quantification score defined in a study published by Rao et al in 2009. The KDRI expresses the relative risk of kidney graft failure for a given donor compared to the median kidney donor from the previous year. Values greater than 1 have higher risk of failure. A KDPI of 80% means that the donor kidney has a greater chance of graft failure than 80% of all kidneys retrieved in the previous year.

The KDPI is calculated using 10 donor characteristics; donor age, height, weight, ethnicity, history of hypertension and diabetes, cause of death, serum creatinine, hepatitis C status, and donation after circulatory death status.

The equation is complicated but here is the OPTN online KDPI calculator.

·      The lower the KDPI the better the kidney.

These two concepts will replace the current categories of SCD and ECD.

SCD will be the equivalent of KDPI of 85% or less. ECD will be equivalent to greater than 85%.

Waiting time calculation

With the new rules the waiting time will be calculated from when the recipient reached a GFR of 20ml/min or less or when they started on RRT even if they were listed after this. Thus, waiting times will be backdated. Waiting time points will be score as fractions of a year, number of days divided by 365.

The current system assigns the wait time when the candidate is listed.

Access for highly sensitized recipients

The new system includes additional priority for recipients that are highly sensitized. This is a sliding scale points system based in calculated PRA starting at a CPRA of 20%. Points on this scale are weighted significantly in favour of those with CPRA over 98%. 

The new system will also facilitate the offer of kidneys from certain blood type A donors (A2 and A2B) to type B recipients in an effort to reduce the wait time for these recipients.

CPRA (%)	Points
0–19	0
20–29	0.08
30–39	0.21
40–49	0.34
50–59	0.48
60–69	0.81
70–74	1.09
75–79	1.58
80–84	2.46
85–89	4.05
90–94	6.71
95	10.82
96	12.17
97	17.3
98	24.4
99	50.09
100	202.1

Wider sharing

The ‘payback’ rule will be removed. If a local service receives a well-matched kidney from another donation service they will no longer ‘owe’ a kidney.

Priority point system for new kidney allocation

This scoring system is used to rank recipients in four quartiles of KDPI.

KDPI <20%; 21 – 34%; 35 – 85%;  >85%

Within each quartile there is also a kidney allocation classification system based on location/OPO, ABDR mismatch, CPRA and blood group.

It is my understanding that EPTS determines which quartile a recipient is ranked in.

Factor	Points Awarded
For qualified time spent waiting	1 per year (as (1/365 per day)
Degree of sensitization (CPRA)	0–202
Prior living organ donor	4
Pediatric candidate if donor KDPI 35%	1
Pediatric candidate (age 0–10 yr at time of match) when offered a zero antigen mismatch	4
Pediatric candidate (age 11–17 yr at time of match) when offered a zero antigen mismatch	3
Share a single HLA-DR mismatch with donor	1
Share a zero HLA-DR mismatch with donor	2

This new system seems fair and is an effort to get the most out of each kidney transplanted. It also attempts to get more use out of poorer quality kidneys by more inter OPO sharing.

The full UNOS policy 3.5 statement can be found here.

The use of IVIg in Kidney Disease

It’s time for a quick nephro-centric summary of immune globulin use. Immune globulin, usually administered intravenously (IVIg), is made from pooled human plasma and used for a wide variety of human disease. It contains mostly IgG with various IgA concentrations depending on the preparation and different stabilizers (see sucrose nephropathy below). IVIg has various anti-infections and anti-inflammatory effects via mechanisms that are still incompletely understood. The sphere of renal transplantation is where most nephrologists will see it being administered.

HLA Desensitization

IVIg is incorporated into various desensitization protocols which may decrease preformed anti-HLA antibodies and render a previous positive crossmatch negative. Two broad regimes are (a) high dose IVIg at 2g/kg single dose or monthly and (b) plasmapheresis with low dose IVIg 100mg/kg after each session. The latter regime is likely more beneficial when an appreciable level of sensitization is present and rituximab may be also be added. The immunomodulatory mechanisms at play may include neutralizing donor-reactive antibodies, reducing anti-HLA antibody formation and the inhibition of complement-dependent endothelial injury.

Antibody-Mediated Rejection (AMR)

IVIg is generally incorporated into a multi-targeted regimen for AMR, usually at least 1g/kg given after plasmapheresis. My own experience is with 2g/kg at the end of the final plasmapheresis sessions. It must be noted that IVIg may interfere with anti-HLA titers, causing false-positive results so it is important to send levels before administering IVIg.

Transplant Infectious Disease

BK Polyoma virus nephropathy (PVN): IVIg may have a role in the treatment of (PVN), particularly in cases where acute rejection co-exists or is suspected. IVIg presumably contains anti-BK antibodies, as the virus is ubiquitous in the general population. However, whether these antibodies are neutralizing or not is unknown. As the cornerstone of PVN treatment is immunosuppression reduction, coexistent acute rejection presents a difficult scenario with IVIg being attractive due to its anti-infective and immunomodulatory properties. Other post-transplant infectious complications where IVIg may be useful include Parvovirus B19 (which may cause severe anemia or an FSGS renal lesion) and possibly resistant CMV infection. The use of IVIg in these settings is usually in conjunction with a decrease in the burden of immunosuppression.

Glomerular disease

IVIg has been used without much convincing evidence for a variety of glomerular pathologies. These include an uncontrolled series of 11 patients with severe IgA Nephropathy given monthly doses of 2g/kg. A decrease in proteinuria and stabilization of GFR was observed. Other unconvincing reports for IVIg use in glomerular disease include a small study in idiopathic membranous nephropathy as well as in lupus nephritis and ANCA associated vasculitis (ref).

Adverse Renal Events

It should be noted that IVIg preparations may uncommonly cause AKI (<1% of infusions). This almost always happens with use of high sucrose-content preparations. IV Sucrose was used in the mid-20^th century for treatment of various edematous states and was associated with AKI, via an osmotic effect causing proximal tubular cell swelling and vacuolization (see JAMA paper from 1942!). IVIg may also cause hyponatremia, as discussed by Nate previously.

Perils of Estimating GFR in Patients with Cirrhosis

In my attempt to highlight nephrology content in non-renal journals, I will this month focus on a series of articles in Hepatology concerning eGFR in cirrhotic patients. We are all aware of the concerns using creatinine-based tools for estimating GFR in this patient cohort given their malnourished, low muscle-mass state. The use of Cystatin-C based equations may theoretically be more informative as this protein is not influenced to the same degree by non-renal factors. However, Cystatin-C is far from perfect and is influenced by sepsis, inflammation and steroid use. Other concerns include the use of the MDRD-6 equation due to the inaccurate determination of albumin (may receive IV infusions) and urea (increased by GI bleed/steroids) in these equations.

As liver patients with renal dysfunction have such a poor prognosis, they are prioritized for liver transplant by way of inclusion in the MELD score, the prognostic tool used to allocate liver allografts. Since adopting MELD, the number of combined liver-kidney transplants (cLKT) has continued to grow, with cLKT considered when GFR<30mls/min and sometimes at higher eGFR. As the demand for kidneys continues to outstrip supply, nephrologists in particular have legitimate concerns regarding the potential for inappropriate use of precious renal allografts in cLKT. This may occur if eGFR underestimates true GFR as may occur with creatinine-based equations. Also concerning is overestimation of true GFR resulting in denial of cLKT where it may actually be indicated, leading to inferior patient outcomes. (See the post by Andrew regarding combined liver-kidney transplant allocation).

Francoz et al studied 300 patients with cirrhosis being evaluated for transplant that had iohexol clearance measured. This was compared to MDRD-4, MDRD-6 and CKD-EPI equations (all using creatinine only) and found that MDRD-6 was the most accurate although it did underestimate true GFR and all 3 equations had poor correlation (R2 0.37-0.4). MDRD-4 and CKD-EPI overestimated GFR especially in those with GFR<60mls/m.

DeSouza et al also looked at patients being evaluated for transplant (n=202) and measured GFR using inulin clearance. Throughout all severities of cirrhosis, Cystatin-C equations were superior with CKD-EPI (Cys-C) the best, compared to creatinine-based MDRD & CKD-EPI methods (which significantly over-estimated true GFR). Of note it outperformed CKD-EPI (creatinine-cystatin-C combined).

Mindikoglu et al examined 72 outpatients with stable cirrhosis comparing CKD-EPI (creatinine-cystatin-C combined) to 24-hour creatinine clearance, Cockcroft-Gault equation and multiple other creatinine-based methods including MDRD & CKD-EPI. Their gold standard was iothalamate clearance. CKD-EPI (creatinine-cystatin-C) performed better than all others including CKD-EPI (Cys-C), unlike DeSouza et al.

Confusing right? What we can take away from these useful studies is that Cystatin-C based equations may be better than creatinine alone equations (remember Francoz et al did NOT use Cystatin-C). However, it should be noted that the diagnostic performance of the best equations in the studies was still markedly lower than reported in validated normal populations. 
My feeling is that in borderline cases when a cLKT is being considered, we need additional data. I would consider a borderline case stable renal dysfunction in the eGFR 20-50mls/min range (arbitrary I know!), not including co-existent ESLD/ESRD or obvious acute hepatorenal cases which will recover with a functioning liver allograft. As renal biopsy is usually not desirable in patient with chronic liver disease, it seems sensible to actually measure GFR in these cases. This appears to be the prudent approach to take to strike a balance between providing a kidney to those who need it and not inadvertently denying an organ to a wait-listed ESRD patient.

Live Kidney Donation: What’s the risk?

As ESRD prevalence continues to increase, the kidney transplant list continues to grow meaning longer waiting times for deceased donor transplantation. Living donation (LD) provides the best outcomes for patients with ESRD and is considered safe for the donor when they are screened effectively. However, although we have data demonstrating low morbidity and mortality associated with living donor nephrectomy, our longer term data has traditionally been flawed. This is primarily because previous studies examining the long-term risk associated with LD has used the general unscreened population as comparators. Individuals who are accepted as living donors have passed rigorous screening and are therefore a well group, likely more so than matched general population controls. A study from Norway included controls matched for age, race and year of birth and showed overall and cardiovascular mortality was lower for kidney donors. A US study employed NHANES controls who were matched for age, sex, BMI and race and reported equivalent risk of ESRD and patient survival. Therefore, our counselling of potential donors was limited to comparisons to the general population where we could point to no increased renal or patient survival risk but we had little data on actual risk of similarly matched controls who did not donate. In recent months we have 2 new studies which give us more accurate data.

The first study was published in KI and included over 1900 kidney donors from Norway between 1963 and 2007. Crucially, the control group comprised individuals deemed eligible for donation (n>32,000). Eligibility was determined from a population cohort with BP<140/90 mm Hg (on no anti-hypertensives), BMI<30 kg/m² who rated their health as ‘good’ or ‘excellent’. Individuals were excluded if they had diabetes or cardiovascular disease. Note that the authors had no data on renal function or albuminuria for the controls. The results demonstrated that donors had a significantly increased long-term risk for ESRD (hazard ratio 11.38!), cardiovascular mortality (HR 1.40) and all-cause mortality (HR 1.30). Of note, 1519 of the donors were first-degree relatives, all cases of ESRD occurred in living related donors and the etiology was immunological in nature, reflecting a likely genetic component to the renal disease in the donors.

Another study recently reported in JAMA from the US included a cohort of >96,000 kidney donors between 1994 & 2011, >20,000 matched controls from NHANES III and examined ESRD risk alone. Controls were gathered by excluding those with identified contraindications to kidney donation (9364 qualified as eligible). They were matched by age, sex, race, educational background, BMI, BP and smoking history. Over a median follow up of 7.6 years, the donors had an increased risk of ESRD. Specifically, the risk of ESRD was 30.8/10,000 in donors V 3.9/10,000 in the matched non-donor controls (P <0.001). The risk was particularly high in black individuals (risk of 74.7/10,000 in donors V 23.9/10,000 in non-donors). Interestingly, white donors (22.7/10,000) had a similar risk of ESRD to the black non-donors with white non-donors having extremely low risk of ESRD in this cohort (0.0/10,000; p<0.001 V white donors). The lifetime risk of ESRD in donors was still significantly lower than unscreened non-donors (i.e. general population) at 90/10,000 V 326/10,000 (see figure).

These studies reaffirm our belief that lifetime risk of ESRD in LD is no higher than in the general demographically-matched population. However the new data suggest that ESRD risk is unsurprisingly higher than healthy screened controls, deemed eligible for donation but who have not donated. The ESRD risk for donation appears to be particularly increased for African Americans, likely due to genetic factors such as presence of APOL1 risk variants. However, the overall magnitude of the risk is small and I think the findings are reassuring. The mortality data from the Norwegian study is not particularly surprising given the robust association between reduced kidney function and mortality in the general population. These studies still have limitations including data ascertainment differences between donors and controls. Also, the control groups may not be perfect but do represent an improvement over previous studies using the unscreened general population. We are now is a position to counsel our living donors with more accuracy regarding the risks of living donation. In my experience, most living donors are happy to accept a small future risk of adverse outcome to donate to a loved one.

Hepatitis B and kidney transplantation

Prior HBV infection is not a contraindication to kidney transplantation. 

It is critical to evaluate patients with serologies and HBV DNA viral load prior to transplant. Most patients should also undergo liver transplant biopsy to exclude significant fibrosis/cirrhosis.
Patients with low risk of reactivation are antiHBc positive and HBsAb positive. Those at higher risk of reactivation have + HBV VL and/or + HBeAg. Those patients with cirrhosis or portal hypertension would benefit of a combined liver/kidney transplant.

The risk of reactivation of HBV under long-term immunosuppression in hepatitis B core antibody-positive, hepatitis B surface antigen (HBsAg)-negative transplant recipients was evaluated over a 3-yr period in 49 transplant recipients (27 liver, 18 kidney, 4 pancreas); 37 recipients (76%) were HBsAb-positive at transplantation (Duhart, Honaker et al. Transp Infect Dis 2003). There was no incidence of HBV reactivation defined as recurrence of HBsAg and/or HBV DNA positivity, suggesting that the risk of reactivation of HBV in hepatitis B core antibody-positive, HBsAg-negative transplant recipients was low with immunosuppression. In the absence of HBsAg positivity, the reactivation of HBV should be assessed using HBV viral loads. 

Do patients with HBV infection benefit from kidney transplantation? 
Recent reports suggest that renal and patient outcomes are comparable to non-HBV infected patients, however, HBV+ patients do carry a 5x fold higher risk of liver failure. Reddy et al. reported no difference in the five-year patient or graft survival between 1346 HBsAg-positive and 74,335 HBsAg-negative recipients who were transplanted between 2001 and 2007 (85.3 versus 85.6 percent, respectively, for patient survival and 74.9 versus 75.1 percent, for graft survival) (Reddy, Sampaio, et al. CJASN 2011).

When should HBV+ patients be transplanted? 
In patients with no evidence of active HBV infection (negative HBV DNA viral load) or cirrhosis/portal hypertension, they may proceed with kidney transplantation. 

How should we manage HBV+ after kidney transplantation?
Prophylaxis with anti-viral therapy is recommended for at least 2 years in order to prevent reactivation. The ideal anti-viral agent is not known though entecavir is commonly used (lower HBV resistance) followed by lamivudine. 
All patients should be placed on a low intensity immunosuppressive regimen, avoiding T cell depleting agents. 
HBV DNA levels should be checked every three to six months to ensure viral suppression and for early detection of virologic breakthrough.

*Patients who are HBsAg neg, anti-HBs neg, but anti-HBc + may develop HBV reactivation after kidney transplantation, but the risk is relatively low. It is controversial whether these patients would benefit from routine antiviral prophylaxis.

Addendum: image from medasend.com