How Best to Detect Microalbuminuria in Diabetic Patients?

How does the use of reagent strips for urine testing compare with quantitative 24-hour urinary protein measurement for determining a patient's risk of diabeti nephropathy?

Robert P Blereau, MD
Morgan City, LA

These two tests are used for distinctly different purposes. The chemically impregnated reagent strip Chemsirip Micral^® is designed for the semiquantitative determination of microalbuminuria. The test can be done on any spot urine sample; however, it is recommended that three separate morning samples be collected and analyzed within a given week. While there are other requirements for testing and sampling, this is essentially a dipstick test that detects albumin in a concentration slightly great than the normal level of 15 to 20 mg/L Because other urinary protein assays, such as Albustix^® and Chemstrip P^® cannot detect this amount (their thresh old is 10 times higher), monitoring low albumin concentrations requires a specific reagent strip, such as Chemstrip Micral.

The test strip measures albumin levels in increments of 20, 50, and 100 mg/L. Higher levels can be determined by diluting the urine. For example, mix one part urine to two parts water, and multiply the value by three to obtain the result.

Since albumin appears in the urine before other renal problems surface screening for its presence is helpful in assessing renal function. This is parti( larly important for patients with diabetes mellitus: 25% of those who undergo dialysis for end-stage renal disease have diabetic nephropathy. If the test doe not reveal microalbuminuria, a 24-hour urine collection is unnecessary because it would show normal levels of protein excretion.

Thus, I recommend using the Micral reagent strip for annual urine testing in all diabetic patients. If the test reveals albuminuria, obtain a 24-hour urine collection to quantify the protein loss. Urinary albumin excretion rates 30 to 300 mg/d signal incipient nephropathy; values greater than 300 mg/d i dicate overt nephropathy. Also, measure creatinine clearance when the 24-hour urine collection is performed. Future urine tests can be used to monitor further renal changes.

To reduce urinary albumin excretion, a growing number of endocrinologists are adding an angiotensin-converting enzyme inhibitor or an angiotensin II receptor antagonist to the regimens of diabetic patients. These agents are equally effective in decreasing microalbuminuria.¹

The results of the Diabetes Control and Complications Trial showed that intensive insulin therapy reduced nephropathy by 54%. This was accomplish by lowering hemoglobin Aic levels by almost 2 percentage points.²

Eric A. Orzeck, MD
Clinical Associate Professor of Medicine
Baylor College of Medicine
Houston

REFERENCES:

1. Ravid M, Savin H, Jutrin I, et al. Long-term stabilizing effect of angiotensin-converting enzyme inhibition on plasma creatinine and on proteinuria in normotensive type II diabetic patients. Ann Intern Med 1993; 118:577-581.

2. The Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus N Engl J Med 1993;329:977-986.

[Editor's note: Trade names have been used solely to distinguish between reagent strips with various degrees of sensitivity. CONSULTANT'S general editorial policy is to use generic names.]

This article appeared in the October 1997 issue of Consultants: Consultations in Primary Care Vol 37. Issue 10 p. 2541