PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Microalbuminuria is defined as a small or moderate increase of albumin excretion in the urine. A confirmed albumin:creatinine ratio (ACR) of 3 mg/mmol or more should be regarded as clinically significant.
The criteria for clinically significant proteinuria have been changed from an ACR of 30 mg/mmol or more to 3 mg/mmol or more. This is because there is evidence that the risk of adverse outcomes is a continuum and starts at an ACR well below 30 mg/mmol.
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Urinary albumin or urinary protein loss should be quantified for:
- People with diabetes.
- People without diabetes with a glomerular filtration rate (GFR) of less than 60 ml/min/1.73 m2.
- People with a GFR of 60 ml/min/1.73 m2 or more if there is a strong suspicion of chronic kidney disease (CKD).
The National Institute for Health and Care Excellence (NICE) guidance has recommended that an early morning urinary ACR should be used in preference to other tests of proteinuria, as ACR offers greater sensitivity for the detection of lower but clinically significant levels of proteinuria. This is also a more convenient test than a 24-hour collection.
Urinary ACR should be used in preference to protein:creatinine ratio (PCR), as it has greater sensitivity than PCR for low levels of proteinuria. However, PCR can be used as an alternative for quantification and monitoring of levels of proteinuria of ACR of 70 mg/mmol or more. ACR is the recommended method for people with diabetes.
These approximate equivalents may be useful:
- ACR 30 mg/mmol = PCR 50 mg/mmol = urinary protein excretion 0.5 g/24 hours.
- ACR 70 mg/mmol = PCR 100 mg/mmol = urinary protein excretion 1 g/24 hours.
NB: false positive results can occur after heavy exercise or with urinary tract infection.
For the initial detection of proteinuria, if the ACR is between 3 mg/mmol and 70 mg/mmol, this should be confirmed by a subsequent early morning sample. If the initial ACR is 70 mg/mmol or more, a repeat sample need not be tested.
The Kidney Disease Improving Global Outcomes ACR categories for ACR are as follows:
- A1: ACR <3 mg/mmol - normal to mildly increased.
- A2: ACR 3-30 mg/mmol - moderately increased.
- A3: ACR >30 mg/mmol - severely increased.
Significance of microalbuminuria
Microalbuminuria is associated with generalised endothelial destruction and has been shown to be an independent risk factor associated with diabetes, CKD, cardiovascular disease, hypertension, venous thromboembolism and all-cause mortality.
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. However, it is recommended that annual screening of a first-pass morning urine specimen for microalbuminuria should be arranged for all people with type 1 or type 2 diabetes.
Markers of kidney disease include albuminuria (ACR more than 3 mg/mmol), urine sediment abnormalities, electrolyte and other abnormalities due to tubular disorders, abnormalities detected by histology, structural abnormalities detected by imaging, and a history of kidney transplantation. Patients should be tested for proteinuria if they have any of the following risk factors:
- GFR ≤60 ml/min/1.73 m2.
- Cardiovascular disease.
- Structural renal tract disease, multiple renal calculi or prostatic hypertrophy.
- Multisystem diseases with potential kidney involvement - eg, systemic lupus erythematosus.
- Family history of CKD stage 5 or hereditary kidney disease.
Increased ACR and decreased GFR are associated with increased risk of adverse outcomes for patients with CKD. Increased ACR and decreased GFR in combination multiply the risk of adverse outcomes.
People with CKD and an ACR of 70 mg/mmol or more should be referred for specialist assessment, unless this is already known to be caused by diabetes and already appropriately treated. Patients with an ACR of 30 mg/mmol or more together with haematuria should also be referred.
Microalbuminuria has been shown to be an independent predictor for coronary heart disease, cardiovascular disease and all-cause mortality in the general population.
In patients with significant proteinuria, important objectives of therapy to delay the progression of CKD are to optimise blood pressure control and reduce proteinuria. All patients should be offered angiotensin-converting enzyme (ACE) inhibitors or angiotensin-II receptor receptor antagonists. See the separate Chronic Kidney Disease article.
See the separate Diabetic Nephropathy article.
Further reading & references
- Chronic kidney disease: early identification and management of chronic kidney disease in adults in primary and secondary care; NICE Clinical Guidelines (July 2014)
- Mahmoodi BK, Gansevoort RT, Veeger NJ, et al; Microalbuminuria and risk of venous thromboembolism. JAMA. 2009 May 6;301(17):1790-7. doi: 10.1001/jama.2009.565.
- Diabetes (type 1 and type 2) in children and young people: diagnosis and management, NICE Guidance (Aug 2015)
- Type 2 diabetes. The management of type 2 diabetes; NICE (May 2009 last modified: March 2014)
- Xia F, Liu G, Shi Y, et al; Impact of microalbuminuria on incident coronary heart disease, cardiovascular and all-cause mortality: a meta-analysis of prospective studies. Int J Clin Exp Med. 2015 Jan 15;8(1):1-9. eCollection 2015.
- Hypertension: management of hypertension in adults in primary care; NICE Clinical Guideline (August 2011)
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Hayley Willacy
Dr Colin Tidy
Dr Laurence Knott