Measuring albuminuria or proteinuria: does one answer fit all?

Measurement of proteinuria is critical for diagnosing and monitoring kidney disease. A variety of measures are available to clinicians and can identify all urinary proteins (proteinuria) or urine albumin alone (albuminuria). Proteinuria and albuminuria can be measured in either a random urine sample or a timed urine collection (often over 24 hours). Although an international guideline advocates the use of the urinary albumin-to-creatinine ratio for most purposes, this measure is not universally available worldwide and historically has been more costly than alternatives. In addition, there may be important differences in accuracy between the albumin-to-creatinine ratio and others based on magnitude of albuminuria, sex, and certain clinical contexts. In this mini review, we review recommendations from international guidelines and discuss specific contexts where the optimal measure of proteinuria is unclear and, in some situations, controversial. We discuss the evidence supporting current recommendations for choice of measure, including the clinical settings of glomerulonephritis, transplantation, and pregnancy. We also discuss how patient sex and cost may impact this decision.