Proteinuria thresholds are irrational: a call for proteinuria indexing.

Current guidelines for chronic kidney disease (CKD) diagnosis, referral and management are based on absolute thresholds of proteinuria/albuminuria with no reference to the residual nephron mass or function. This is illogical since the severity of proteinuria is a direct reflection of the number of filtering nephrons as well as their pathology and the capacity of the tubules to reabsorb filtered protein/albumin. The current simplistic approach to proteinuria may also compromise its usefulness as a robust guide to appropriate treatment, e.g. preferential use of inhibitors of the renin-angiotensin-aldosterone system. The routine measurement of the urinary protein/albumin:creatinine ratio (PCR/ACR) and estimated glomerular filtration rate (eGFR) gives rise to the opportunity to index proteinuria for renal function (i.e. a PCR:eGFR or ACR:eGFR ratio). Since both PCR/ACR and eGFR are reflections of quantities assessed per unit body surface area, this is a logical approach to the assessment of proteinuria/albuminuria. We advocate a consideration of the benefits of indexing PCR/ACR for eGFR to optimise treatment decisions based on proteinuria/albuminuria.