How is the Micral urine test performed and interpreted for screening microalbuminuria in adult patients with diabetes?

Micral Test Urine

The Micral test is a semiquantitative immunologic dipstick that can be used for rapid screening of microalbuminuria in diabetic patients when quantitative urine albumin-to-creatinine ratio (UACR) testing is not immediately available, but positive results must be confirmed with laboratory-based UACR measurement 1.

How to Perform the Test

Sample Collection

• Use a first morning void urine sample for optimal accuracy 1
• If first morning void is difficult to obtain, collect all samples at the same time of day 1
• Patient should be well hydrated, have not eaten within 2 hours, and have not exercised 1
• Test the sample immediately or within a short time frame

Test Procedure

• Dip the Micral test strip into the urine sample
• Wait 1 minute for color development (if massive leucocyturia or erythrocyturia is present, wait an additional 1-2 minutes) 2
• Read the color scale on the strip, which provides semiquantitative results in mg/L
• The test detects albumin concentrations from 0 to 100 mg/L using an immunologic reaction 2

Interpretation

Cutoff Values

• Microalbuminuria range: 20-200 mg/L on spot urine 3, 4
• The optimal cutoff for screening is approximately 20-30 mg/L 5, 6
• Results ≥20 mg/L should be considered positive for screening purposes

Performance Characteristics in Diabetic Patients

The test demonstrates good but not perfect accuracy 5, 6, 7:

• Sensitivity: 83-96% (most studies show ~90-95%)
• Specificity: 80-96%
• Positive predictive value: 69-95%
• Negative predictive value: 88-99%

Critical Limitations and Pitfalls

Must Confirm Positive Results

Semiquantitative or qualitative screening tests should be positive in >85% of individuals with moderately increased albuminuria, but positive results require confirmation with quantitative laboratory UACR 1. The guideline explicitly states that dipstick screening is "susceptible to false-negative and false-positive determinations" and "will need to be confirmed by UACR values in an accredited laboratory" 8.

Factors Affecting Accuracy

• Urine concentration: The test is affected by hydration status 8, 6
• Temperature: Samples <10°C produce falsely low readings 2
• Medications: Oxytetracycline causes falsely elevated readings 2
• Urine sediment: Massive leucocyturia or erythrocyturia may interfere with the chromatographic process 2
• Specific gravity: Concomitant measurement of specific gravity helps identify false positives and negatives 6

Clinical Algorithm

1. Screen annually starting at diabetes diagnosis for type 2 diabetes 1
2. If Micral test is negative (<20 mg/L): Repeat annually
3. If Micral test is positive (≥20 mg/L):
   • Confirm with laboratory UACR measurement on a first morning void specimen 8, 1
   • Do not make treatment decisions based on Micral test alone 7
4. If UACR confirms microalbuminuria (30-300 mg/g creatinine):
   • Repeat every 6 months if eGFR <60 mL/min/1.73 m² 1
   • Initiate appropriate treatment (ACEI/ARB, blood pressure control, glycemic control)

When to Use Quantitative UACR Instead

It is better to simply collect a spot urine sample for UACR rather than using semiquantitative dipsticks 8. The Micral test should only be used "when quantitative tests are not available" 1. In settings with laboratory access, proceed directly to UACR measurement rather than screening with dipsticks, as this avoids the need for confirmatory testing and provides more accurate quantification for treatment decisions.