Chemical Pathology

Notes

  • Proteinuria is an important indicator of kidney disease and its risk of progression.
  • Albumin:creatinine ratio (ACR) is the preferred test for detection of small amounts of albumin in the urine. Proteinuria and microalbuminuria are both signs of renal involvement in the disease process and are risk factors for cardiovascular morbidity and mortality. Measurement forms part of the diagnosis, staging and monitoring of 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
  • cardiovascular disease (ischaemic heart disease, chronic heart failure, peripheral vascular disease or 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

6ml plain urine tube






Storage/transport

Send at ambient temperature to the laboratory. If unavoidable, samples may be stored refrigerated overnight.

Required information

Relevant clinical details including reason for the test, any current UTI or haematuria and whether the sample is an early morning urine.

Turnaround times

Results are normally available within 3 days of receipt by the laboratory.

The test can be ordered as an urgent request.

Reference ranges

Urine ACR

Adult reference range (NICE CG182):

<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.
  • Please see CKD information on G-Care for more information and for referral criteria.

Urine ACR in pregnancy (NICE NG133): if using albumin:creatinine ratio as an alternative to protein:creatinine ratio to diagnose pre-eclampsia in pregnant women with hypertension, use 8 mg/mmol as a diagnostic threshold. If the result is 8 mg/mmol or above and there is still uncertainty about the diagnosis of pre-eclampsia, consider re-testing on a new sample, alongside 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.

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 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.

Problems associated with sampling:

  • 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. It is possible, however, to lose significant amounts of other proteins of lower molecular size (e.g. in renal tubular disease or in light chain disease) without necessarily seeing an increase in albumin loss.
  • Some drugs may cause an analytical interference in assessing protein levels.

Further information

Lab Tests Online Albumin:Creatinine Ratio

NICE Guideline: Chronic Kidney Disease pathway (CG182, 2014)

NICE Guideline: Hypertension in pregnancy: diagnosis and management (NG133, 2019)

G-Care Guidance: CKD


Page last updated: 09/11/2020

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