Saturday, September 19, 2009

"The eGFR Consult"

Cool new resource for all those iPod/iPhone (or whatever your MP3 player or PDA of choice happens to be): the ASN Kidney News podcast series. I have been listening to these during days in the lab where I happen to be carrying out some mind-numbingly repetitive task.

The most recent podcast is a conversation with Dr. Richard Glassock of UCLA in which he discusses how he approaches "the eGFR consult", a term which refers to the increasingly common situation in which a primary care physician refers an elderly patient to a nephrologist based solely on an estimated GFR that is determined to be abnormal. Presently, many hospitals will report every creatinine with a calculated GFR value based on the MDRD; often, values below 59 ml/min/1.73 m2 will be "red-flagged" as abnormal. Particularly in low body weight elderly patients, a stable creatinine of "only" 1.2 or 1.3 may come back with an eGFR indicative of CKD.

Dr. Glassock makes the point that we may be putting too much faith in eGFR values. He states that there is poor correlation between eGFR and measured GFR in many instances, that the MDRD Equation by itself is presently unsuitable for approving decision about whether an individual may serve as a live kidney donor, and that we are still waiting for a more universal standardization of creatinine amongst labs.

CKD Stage 3, for instance, makes up a large percentage of the population deemed "CKD" based on current KDOQI guidelines. Yet only a small fraction of these patients will go on to develop ESRD. One potentially useful approach is suggested in Great Britains "NICE Criteria for CKD"--they subdivide CKD Stage 3 in to "A" (eGFR = 45-59 ml/min) and "B" (eGFR = 30-40 ml/min) groups, and furthermore give patients a label of "P-positive" or "P-negative" based on whether or not proteinuria is present. Not surprisingly, individuals who are Stage 3B-P+ have a very high risk of progression of their kidney diseases, whereas individuals who are Stage 3A without proteinuria apparently have no increased risk of reaching ESRD. I think most nephrologists realize this fact (that proteinuria is a useful way of risk-stratifying patients falling into the CKD 3 category), but perhaps modifying the criteria used by PCPs and other physicians might lead to more optimal nephrology referral patterns in the future.

3 comments:

Warren said...

If your lab standardizes Scr to the isotope dilution mass standard, it can be reliably used.

nathanhellman said...

Agreed--but sometimes patients have labs drawn at different facilities, which could potentially use different methods...

One thing I find funny the way our hospital reports the creatinine--it always gives the value to two decimal places (e.g., a creatinine of 1.46). I highly doubt that this degree of accuracy is meaningful--wouldn't rounding up or down make more sense? My brain doesn't need to hold on to that extra info provided by the 2nd decimal place, yet it inevitably does.

Ben said...

Thanks for the shout out, Nathan. I direct the podcast program for ASN. Please let me know if you or any of your readers have ideas for future Kidney News podcasts, or other resources that ASN can provide to benefit renal fellows.

Best,
Ben Carver
ASN
bcarver@asn-online.org