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The importance of effective microalbuminuria testing

Elaine Linnane
BSc(Hons)
Editor
Nursing in Practice

Microalbuminuria is the presence of small but abnormal amounts of the protein albumin in the urine. It often indicates increased permeability of the kidney's small blood vessels - a common complication of diabetes where high blood glucose levels damage small blood vessels, leading to renal disease (nephropathy), cardiovascular disease and retinopathy.
Measurement of urine albumin is also useful in the diagnosis and treatment of hypertension and pre-eclampsia and as a predictor of outcome in critically ill patients.(1,2) It requires special methods of testing, since the tiny amounts of albumin involved in microalbuminuria are not detectable by the standard urine tests used to check for proteins.
A 24-hour urine collection to estimate the albumin excretion rate (AER) is the best method of assessing albumin excretion, but it is time-consuming and expensive and therefore not suitable for large-scale screening. Rather, a random sample of urine is often used to measure the albumin-creatinine ratio (ACR). The ACR varies according to age and sex, but as a general rule men should have an ACR less than 2.5, and women less than 3.5. Point-of-care testing (POCT) devices are available that can give an ACR test result within minutes. At least two or three measurements should be taken before the diagnosis of persistent microalbuminuria is made.

NICE guidelines
The National Institute for Clinical Excellence (NICE) clinical guidelines for the management of type 2 diabetes state that there is evidence to show that early detection of microalbuminuria, with subsequent changes to patient management, can prevent or slow the progression of renal disease and determine the risk of cardiovascular disease.(3) The guidelines recommend that urine albumin be measured at least annually for patients with type 2 diabetes. Moreover, the new General Medical Services (GMS) contract requires GPs to report the percentage of patients with diabetes who have had their urine albumin measured within the last 15 months.(4)
The NICE guidelines for type 2 diabetes state that urine albumin alone or the urine ACR can be measured using a POC or laboratory test specific for microalbuminuria. Microalbuminuria is classified as an albumin concentration >20 but The NICE guidelines for the diagnosis and management of type 1 diabetes differ as urine albumin alone is considered a poor indicator; ACR measurement is preferred.(5)
 
Testing the point-of-care tests available
There are four POCT devices currently available in the UK for microalbuminuria (ACR) monitoring - three semiquantitative and one qualitative:

  • Clinitek(®) Microalbumin Reagent Strips and Clinitek Status(®) Analyzer, by Bayer Diagnostics.
  • Microalbustix(TM) Reagent Strips, by Bayer Diagnostics.
  • Chemstrip(®) Micral Urine Test Strips, by Roche Diagnostics.
  • ImmunoDip(®) Test for Urinary Albumin, by Diagnostic Chemicals Limited (DCL).

A recent study compared these devices.(6) The study first assessed the analytical potential of the devices under ideal conditions by testing, in pooled urine, a series of solutions of increasing albumin/creatinine concentration. Patient samples were then compared with a laboratory test to show how device performance was influenced by the variable constituents of different urine samples. Finally, device accuracy was compared with consensus reference values in samples circulated by an External Quality Assessment Scheme.
All the devices were found to be easy to use and provided results in 1-3 minutes.
The Clinitek Status urine strip reader was reliable and demonstrated some improvement in analytical performance compared with visual measurement, but it had difficulty distinguishing between the 30 and 80mg/l concentrations. An advantage is that the device records and prints out a copy of the results, including operator and patient ID.
The Microablustix strips are chemically identical to the Clinitek strips but are read visually. They showed acceptable performance, but there was significant overlap between the 10 and 30mg/l colour blocks.
The Micral strips generally performed well, but there was some difficulty distinguishing between the negative and 20mg/l concentrations.
The ImmunoDip, a simple qualitative test giving only positive or negative results, demonstrated good performance. The study showed that it had particularly good discrimination at the clinically important 20mg/l concentration level and concluded it to be a very suitable screening device to detect microalbuminuria. The other devices were less effective at the 20mg/l level and in some cases showed poor discrimination at higher concentrations.

References

  1. Waugh J, Kilby M, Lambert P, et al. Validation of the DCA 2000 ­microalbumin: creatinine ratio ­urinanalyzer for its use in pregnancy and preeclampsia. Hypertens Pregnancy 2003;22:77-92.
  2. MacKinnon KL, Molnar Z, Lowe D, et al. Use of microalbuminuria as a predictor of outcome in critically ill patients. Br J Anaesth 2000;84:239-41.
  3. National Institute for Clinical Excellence Inherited Clinical Guideline F. Management of type 2 diabetes, renal disease prevention and early ­management (N00061). London:NICE; February 2002.
  4. Available from URL: http://www.nhsconfed.org/gms/gms_contract
  5. National Institute for Clinical Excellence Clinical Guideline 15. Type 1 diabetes: diagnosis and management of type 1 diabetes in young people and adults. London:?NICE; July 2004.
  6. Burtonwood C, Piggott C, Halloran S. MHRA. Point of care devices for detection and semi-quantitation of microalbuminuria. London: Department of Health; 2004.