A study of the relationship between albuminuria, proteinuria and urinary reagent strips

Background: The aims of this study were to examine the relationship between proteinuria and albuminuria and to assess the equivalence between the albumin to creatinine ratio (ACR) and the protein to creatinine ratio (PCR) at the cut-offs recommended by the National Institute for Health and Clinical Excellence (NICE) guidance on chronic kidney disease. The sensitivity and specificity of the reagent strips used in our laboratory for the detection of clinical proteinuria was also assessed. Methods: Urine samples (n = 117) were screened for protein using the Bayer Multistix 10SG and read manually. Urinary total protein and creatinine was measured on the Roche P Modular by the benzethonium chloride and kinetic Jaffe methods, respectively. Urinary albumin was measured by immunoturbidimetry on the Roche Cobas Mira. Results: The relationship between urinary protein and albumin loss was non-linear (P < 0.05). As urinary protein loss increased the percentage of albumin to total protein increased. At the NICE guidance recommended cut-offs for clinical proteinuria (ACR >= 30 mg/mmol and PCR >= 50 mg/mmol) there was one discordant result between ACR and PCR (ACR <30 mg/mmol and IPCR >50 mg/mmol). The Bayer Multistix 10SG had a sensitivity and specificity of 97% and 62%, respectively, for the detection of clinical proteinuria compared with ACR. Conclusions: The proportion of urinary total protein attributable to albumin changes with concentration. There was only one discordant result between ACR and PCR: therefore either ratio may be used for the identification of clinical proteinuria. As a screening test for proteinuria, the Bayer Multistix 10SG had an acceptable sensitivity but poor specificity.