Urinary albumin:creatinine ratio

The urinary albumin:creatinine ratio is a useful measure of renal function used in diabetic renal disease.

The urinary albumin:creatinine ratio is measured using the first morning urine sample where practicable.

Microalbuminuria is defined as: albumin:creatinine ratio >2.5mg/mmol (men) or >3.5mg/mmol (women) or albumin concentration >20mg/l.

Proteinuria is defined as: albumin:creatinine ratio >30mg/mmol or albumin concentration >200mg/l.

Notes:

• NICE suggest that (2):
  • all people with diabetes, and people without diabetes with a GFR less than 60 ml/min/1.73 m^2, should have their urinary albumin/protein excretion quantified. The first abnormal result should be confirmed on an early morning sample (if not previously obtained)
  • quantify by laboratory testing the urinary albumin/protein excretion of people with an eGFR 60 ml/min/1.73 m2 or more if there is a strong suspicion of CKD
  • for the initial detection of proteinuria, if the albumin:creatinine ratio (ACR) is 30 mg/mmol or more (this is approximately equivalent to protein: creatinine ratio (PCR) 50 mg/mmol or more, or a urinary protein excretion 0.5 g/24 h or more) and less than 70 mg/mmol (approximately equivalent to PCR less than 100 mg/mmol, or urinary protein excretion less than 1 g/24 h) this should be confirmed by a subsequent early morning sample
    • If the initial ACR is 70 mg/mmol or more, or the PCR 100 mg/mmol or more, a repeat sample need not be tested
  • in people without diabetes consider clinically significant proteinuria to be present when the ACR is 30 mg/mmol or more (this is approximately equivalent to PCR 50 mg/mmol or more, or a urinary protein excretion 0.5 g/24 h or more)
  • in people with diabetes consider microalbuminuria (ACR more than 2.5 mg/mmol in men and ACR more than 3.5 mg/mmol in women) to be clinically significant
  • do not use reagent strips to identify proteinuria unless they are capable of specifically measuring albumin at low concentrations and expressing the result as an ACR
  • to detect and identify proteinuria, use urine ACR in preference, as it has greater sensitivity than PCR for low levels of proteinuria. For quantification and monitoring of proteinuria, PCR can be used as an alternative. ACR is the recommended method for people with diabetes
  • regard a confirmed ACR of 3 mg/mmol or more as clinically important proteinuria
  • classification of ACR

• * Relative to young adult level ** Including nephrotic syndrome (ACR usually >220 mg/mmol)

• the Renal Association note that (3):
  • use of early morning urines to measure albumin creatinine ratio (ACR) gives a more accurate estimate of 24h urine albumin, though random samples have acceptable performance
  • additionally, early morning urines allow the exclusion of orthostatic proteinuria. In orthostatic proteinuria significant urinary protein is excreted when erect, but when recumbent the urinary protein is completely normal. This usually occurs in young adults, and has no long-term consequences

Reference:

• (1) MeReC Briefing 2004;26:1-8.
• (2) NICE (July 2014). Chronic Kidney Disease - Early identification and management of chronic kidney disease in adults in primary and secondary care
• (3) UK Renal Association (2011). Detection, Monitoring and Care of Patients with CKD