A Comparison of Urinary Albumin-Total Protein Ratio to Phase-Contrast Microscopic Examination of Urine Sediment for Differentiating Glomerular and Nonglomerular Bleeding

Background: Hematuria can be classified as either glomerular or nonglomerular, depending on the bleeding source. We recently reported that urinary albumin-total protein ratio is potentially useful for identifying the source of hematuria. Study Design: Diagnostic test study. Setting & Participants: 579 fresh urine specimens with microhematuria (≥5 red blood cells/high-power field) collected from patients with the source of the hematuria confirmed on histopathologic and/or imaging studies and clinical criteria assessed. Index Test: Each urine specimen was evaluated morphologically by using phase-contrast microscopy and biochemically by using urinary albumin-total protein ratio, albumin-creatinine ratio, and total protein-creatinine ratio. Reference Test: Each patient had a definitive clinical diagnosis established by means of biopsy (64.4%), imaging studies (21.2%), and routine optimal microscopic examination of urine sediment (14.3%). Results: Of 579 specimens, 329 were obtained from patients with glomerular disease and 250 were obtained from patients with nonglomerular disease. Mean urinary albumin-total protein, albumin-creatinine, and total protein-creatinine ratios for those with glomerular versus nonglomerular diseases were 0.73 ± 0.11 versus 0.41 ± 0.14 mg/mg (P < 0.001), 1,110 ± 1,850 versus 220 ± 560 mg/g (P < 0.001), and 1,600 ± 3,010 versus 480 ± 1,160 mg/g (P < 0.001), respectively. The percentage of patients with greater than 3% glomerular red cells was 83.3% versus 24.8% (P < 0.001). Receiver operating characteristic curve analysis showed that areas under the curve for albumin-total protein ratio, albumin-creatinine ratio, and total protein-creatinine ratio were 0.992, 0.781, and 0.688, respectively (P < 0.001, albumin-total protein versus albumin-creatinine; P < 0.001, albumin-total protein versus total protein-creatinine). At cutoff values of 0.59 mg/mg, 71 mg/g, and 265 mg/g, albumin-total protein ratio, albumin-creatinine ratio, and total protein-creatinine ratio had sensitivities and specificities of 97.3% and 100%, 78.9% and 61.1%, and 68.8% and 62.0% for detecting glomerular disease, respectively. Phase-contrast microscopy had sensitivity of 83.3% and specificity of 75.2% for detecting glomerular disease. Limitations: Albumin-total protein ratio cannot be used in patients with urinary total protein less than 5 mg/dL (<0.05 g/L). Use of only 1 sample from 1 patient may not be sufficient to obtain definitive results. Conclusions: Urinary albumin-total protein ratio is much more useful than phase-contrast microscopy for differentiating between glomerular and nonglomerular disease in patients with microscopic hematuria.