Diabetes-related investigations - albumin-to-creatinine ratio test

Role

Urinary albumin-to-creatinine ratio (ACR) is the standard screening test for diabetic nephropathy, detecting microalbuminuria (an early marker of glomerular damage) before overt proteinuria or a significant fall in eGFR develops, enabling earlier intervention to slow progression
Recommended as routine annual screening in both type 1 diabetes (from around 5 years post-diagnosis, or from diagnosis in adults) and type 2 diabetes (from diagnosis, given uncertain disease duration at presentation), reflecting the substantial burden of diabetic nephropathy as a leading cause of chronic kidney disease

Early diabetic glomerular damage increases glomerular basement membrane permeability to albumin before overall filtration function (eGFR) declines - this explains why ACR is a more sensitive early marker than eGFR alone, detecting kidney involvement at a stage when intervention (glycaemic control, blood pressure control, specific renoprotective medication) can still meaningfully slow progression

A spot urine sample is used (rather than requiring a 24-hour collection), with the creatinine ratio correcting for urine concentration variability - results should be confirmed on a repeat sample given biological variability (exercise, infection, and other transient factors can cause false-positive elevation) before labelling a patient with diabetic nephropathy
Combined assessment with eGFR provides the full CKD staging picture (both albuminuria category and eGFR category are used together in current CKD staging)

Confirmed microalbuminuria -> optimise glycaemic and blood pressure control, and initiate/optimise an ACE inhibitor or ARB (or, per current guidance, an SGLT2 inhibitor) given their renoprotective effect independent of blood pressure lowering alone
Progressive rise in ACR despite treatment optimisation should prompt nephrology referral and reconsideration of the diagnosis (excluding non-diabetic causes of proteinuria)

Diabetic nephropathy staging (albuminuria category combined with eGFR category), ACE inhibitor/ARB and SGLT2 inhibitor renoprotective effect, false-positive elevation from transient factors (exercise, infection) requiring confirmatory retesting

A single elevated ACR result should be confirmed on a repeat sample before diagnosing diabetic nephropathy, given genuine biological variability (recent exercise, urinary tract infection, and other transient factors can all cause a false-positive elevation) - acting on a single unconfirmed result risks an inaccurate diagnosis and unnecessary treatment escalation

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