Diagnostic significance of transferrinuria and albumin-specific dipstick testing in primary care patients with elevated office blood pressure.
This study assesses the diagnostic accuracy of transferrinuria and an albumin-specific dipstick assay for detection of renal target organ damage (microalbuminuria) in hypertensive patients in a general practice setting. A spot urine sample of 130 nondiabetic patients with elevated office blood pressure readings (>140 and/or 90 mmHg) was investigated by measuring albumin to creatinine ratio (ACR) and transferrin to creatinine ratio (TCR) and by using an albumin-specific dipstick test (Micral). ACR was considered as comparative gold standard. TCR was elevated (>0.19 mg/mmol) in 26 urine samples (20.0% of the test samples). ACR was raised in 29 samples (22.3% of the test samples). Elevated TCR had a sensitivity of 97% and specificity of 91% for detection of microalbuminuria. Positive predicting value for microalbuminuria was 65%; negative predicting value was 99%. Correlation between ACR and TCR was strong (r=0.96). Dipstick testing for albumin was positive in 23 urine samples (17.7% of the test samples), 27 (20.8%) tests were false positive and six (4.6%) false negative. When dipstick was positive, the sensitivity of detecting microalbuminuria was 79%, and specificity 73%. In conclusion, detection of urinary transferrin in nondiabetic patients with hypertension is strongly associated with urinary albumin excretion. However, assessment of TCR does not identify additional patients with microalbuminuria compared to measurement of ACR alone. The semiquantitative Micral test offers a simple and valuable method to screen hypertensive patients for microalbuminuria in a primary care setting.