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Objective: We recently showed that a urine albumin/total protein ratio (uAPR) <0.4 identifies tubular pathology in proteinuric patients. In tubular disorders, proteinuria is usually of low molecular weight and contains relatively little albumin. We tested the hypothesis that uAPR is useful in identifying tubular pathology related to antiretroviral use in HIV-infected patients., Methods: We retrospectively identified urine protein/creatinine ratios (uPCRs) in HIV-infected patients. A subset of samples had uPCR and urine albumin/creatinie ratio (uACR) measured simultaneously. We classified proteinuric patients (uPCR >30 mg/mmol) into two groups: those with predominantly 'tubular' proteinuria (TP) (uAPR <0.4) and those with predominantly 'glomerular' proteinuria (GP) (uAPR ≥ 0.4)., Results: A total of 618 of 5244 samples from 1378 patients had uPCR ≥ 30 mg/mmol. uAPRs were available in 144 patients: 46 patients (32%) had TP and 21 (15%) GP; the remainder had uPCR <30 mg/mmol. The TP group had a higher fractional excretion of phosphate compared with the GP group (mean 27% vs. 16%, respectively; P<0.01). Patients with TP were more likely to be on tenofovir and/or a boosted protease inhibitor compared with those with GP. In 18 patients with heavy proteinuria (uPCR >100 mg/mmol), a renal assessment was made; eight had a kidney biopsy. In all cases, the uAPR results correlated with the nephrological diagnosis., Conclusions: In HIV-infected patients, measuring uAPR may help to identify patients in whom a renal biopsy is indicated, and those in whom tubular dysfunction might be an important cause of proteinuria and which may be related to antiretroviral toxicity. We suggest that this would be useful as a routine screening procedure in patients with proteinuria., (© 2012 British HIV Association.)