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Microalbuminuria is a urine protein loss of 30 to 300mg/d (not detectable on normal dipstick). Seen with diabetes mellitus, ↑↑ BP, SLE, and glomerulonephritis

Assessing Albuminuria using APCR

Albumin:creatinine ratio usually a first-in-the-morning spot urine sample

• <3 mg/mmol: normal to mildly increased
• 3-30 mg/mmol: moderately increased, relative to young adult level. Regard a confirmed ACR of 3 mg/mmol or more as clinically important proteinuria.
• >30 mg/mmol: severely increased, including nephrotic syndrome (urine ACR usually >220 mg/mmol)

About

• Proteinuria indicates kidney disease and its risk of progression.
• Albumin: creatinine ratio (ACR) is the preferred test
• It measures small amounts of albumin in the urine.
• Microalbuminuria is prognostic for cardiovascular morbidity and mortality.
• Can be useful to stage chronic kidney disease (CKD)
• ACR is the recommended method for people with diabetes.
• Protein: creatinine ratio (PCR), rather than ACR, should be requested where non-albumin proteinuria is suspected.

Indications for Testing

• Diabetes mellitus, Hypertension
• Acute kidney injury
• Ischaemic heart disease
• Chronic heart failure
• Peripheral vascular disease
• Cerebral vascular disease
• Structural renal tract disease
• Recurrent renal calculi or prostatic hypertrophy
• Multisystem diseases with potential kidney involvement – for example, systemic lupus erythematosus
• Family history of end-stage kidney disease or hereditary kidney disease
• Opportunistic detection of haematuria.
• Monitoring patients on certain drugs (penicillamine)

Indications for testing in pregnancy (NICE NG133):

• For assessment of proteinuria in hypertensive disorders of pregnancy, interpret proteinuria measurements for pregnant women in the context of a full clinical review of symptoms, signs and other investigations for pre-eclampsia.
• Use an automated reagent-strip reading device for dipstick screening for proteinuria in pregnant women in secondary care settings. If dipstick screening is positive (1+ or more), use albumin: creatinine ratio or protein: creatinine ratio to quantify proteinuria in pregnant women.
• Do not use first-morning urine void to quantify proteinuria in pregnant women. Do not routinely use 24-hour urine collection to quantify proteinuria in pregnant women.

Sample requirements

• An early morning urine sample in a 6mL plain urine tube

Results ACR: <3 mg/mmol: normal to mildly increased

• 3 - 30 mg/mmol: moderately increased, relative to young adult level. Regard a confirmed ACR of 3 mg/mmol or more as clinically important proteinuria.
• >30.0 mg/mmol: severely increased, including nephrotic syndrome (urine ACR usually >220 mg/mmol)
• A new finding of urine ACR of between 3 and 70 mg/mmol should be confirmed with a first morning urine sample to establish consistent finding and exclude transient elevation due to intercurrent illness.
• If the urine ACR is >70 mg/mmol there is no need to repeat to confirm the result.

Urine PCR Adult reference range: <50 mg/mmol

• Paediatric reference range (<18 years of age): <20 mg/mmol
• Urine PCR in pregnancy (NICE NG133): if using protein: creatinine ratio to quantify proteinuria in pregnant women, use 30 mg/mmol as a threshold for significant proteinuria. If the result is 30 mg/mmol or above and there is still uncertainty about the diagnosis of pre-eclampsia, consider re-testing on a new sample alongside the clinical review.
• Interpret proteinuria measurements for pregnant women in the context of a full clinical review of symptoms, signs and other investigations for pre-eclampsia.

Sample Issues

• Results can be affected by physiological factors such as erect posture, exercise or acute diuresis
• False positive results may be seen with menstrual or seminal fluid, urinary tract infection, contaminated collection containers.
• Urine samples should not be collected after undue exertion or acute fluid loads.
• High urine proteins but normal ACR: Urine ACR is specific for albumin. However, it is possible to lose significant amounts of other proteins of smaller molecular size (e.g. in renal tubular disease or light chain disease) without necessarily seeing an increase in albumin loss.
• Some drugs may cause an analytical interference in assessing protein levels.