Microalbuminuria

Microalbuminuria is defined as excretion of between 30 and 300 mg of albumin a day in the urine.

• Less than 30 mg is insignificant.
• Over 300 mg is albuminuria or macroalbuminuria.

Albumin levels below 300 mg a day are not detectable by standard protein dipstick testing, so any positive result is more severe than "microalbuminuria".

Patients with type 2 diabetes may have microalbuminuria at presentation as they may have had latent disease for years.
This is not usual in type 1 diabetes. Hence it is recommended that annual screening for microalbuminuria should start at diagnosis in type 2 but only after 5 years in type 1.¹

Risk factors

Diabetes and hypertension are both risk factors but together the risk is very high.
Other causes of albuminuria include:

• Glomerulonephritis
• Amyloidosis
• Other forms of nephropathy

All pass through a brief phase of microalbuminuria, but this is short and the diagnosis is usually made with a more substantial proteinuria.

• An early morning urine specimen should be sent for albumin:creatinine ratio (more convenient than a 24 hours collection).²The upper limit of normal is regarded as a urine albumin:creatinine ratio of:
  • 2.5 mg/mmol in men
  • 3.5 mg/mmol in women
  Some laboratories set a limit of 20 mg albumin per litre.
• A positive result should be repeated once or twice in the next month and if it is borderline a full 24 hours urine collection will give a more definitive result.
• Levels below 300 mg a day are not detectable by conventional dipstick testing but there are now some sticks for microalbuminuria available on the market.
• False positive results can occur after heavy exercise or with UTI.
• If a diabetic develops heavy proteinuria, especially in a fairly short space of time, then another cause should be sought.
• The same is true if there is no retinopathy.
• If eGFR falls below 60 mL/min/1.73 m² referral to a nephrologist is recommended.³

NICE advises ACE inhibitors (or angiotensin II receptor antagonists) should be offered to all who:²

• Have CKD and hypertension with an ACR of 30 mg/mmol or more, or
• Have CKD and hypertension with urinary excretion of 0.5 g/24 hours or more

Intensive management of blood pressure and glycaemia in both type 1 and type 2 diabetes has been shown in the DCCT and UKPDS to improve outcome.⁹
For the best outcome for heart and kidneys a combination of blood pressure control, use of ACE inhibitors, statins and aspirin are required.¹⁰