Creatinine: A Cautionary Tale

In recent months I've been seeing a number of referrals for patients with creatinine values in the normal range but eGFR as reported by the lab at below 60ml/min. This is particularly the case in middle aged women. Another group of cases troubling my Primary Care colleagues are male athletes with creatinine levels at or above the upper limit of normal but with no other apparent marker of kidney disease.

Certainly this is reflective of the weakness of using creatinine and creatinine based estimates of GFR as our basis for determining renal function. Unfortunately there are limited clinically applicable alternatives. What do we tell these patients? Do they or do they not have kidney disease?

My approach is the following:
1. Authenticate renal function within the office practice to the extent possible.
2. Check Cockcroft Gault creatinine clearance
3. Check 24 hour or 12 hour urine creatinine clearance
4. Rule out rising creatinine within normal range by reviewing historical data if available
5. Rule out Microalbuminuria or Proteinuria as markers of intrinsic renal disease
6. Rule out CKD risk factors (Hypertension, Diabetes, etc)
7. Consider a renal U/S to evaluate renal size.

If all these data are within normal limits then I reassure the patient and suggest a 6 to 12 month follow up and will repeat the studies to confirm a normal picture. If there remains doubt an Iothalamate measured GFR needs to be obtained. The issue of estimated versus measured GFR is reviewed by Andrew Levey and Lesley Stevens in an excellent article in JASN last year.

For those athletes with elevated creatinine levels I recommend the same process making sure they: discontinue all NSAID use; do not take any creatine based dietary supplements; and limit their meat intake to reasonable levels before performing the testing.

David Steele MD.