The Usefulness of Lordosis Load Test and Urinary Biochemistry in the Diagnosis of Orthostatic Proteinuria

Introduction Renal disease is commonly suspected in patients with proteinuria. Renal biopsy might be considered based on the patient's clinical history and the results of diagnostic tests. However, as orthostatic proteinuria is benign and requires no treatment, it is important to obtain a diagnosis without renal biopsy whenever possible. Therefore, up to now, for the diagnosis of orthostatic proteinuria, in addition to resting urinalysis evaluation (disappearance of proteinuria), we have performed the lordosis load test and urine biochemistry of the samples showing peak proteinuria in a lordosis load test. Method We retrospectively enrolled all patients who visited the pediatric department and underwent the lordosis load test at Kanazawa Medical Center between 2011 and 2020. In the present study, samples with the highest concentrations of protein after the lordosis load test were subjected to general urinary biochemistry and urinary sediment analysis. Patients were followed up with the lordosis load test for several years. Results Enrolled in the study were 68 patients with OP. The mean age at the time of diagnosis was 11.5 years (range, six to 16 years). General urinary tests, urinary sediment, and urinary biochemistry including N-acetyl-beta-D-glucosaminidase (NAG), alpha1-microglobulin(α1MG), and beta 2-microglobulin (β2MG) were normal in all patients with orthostatic proteinuria except one case who was a premature baby. Conclusion If proteinuria disappears after two hours of rest, and urinary biochemistry of the samples showing peak proteinuria in the lordosis load test is normal, orthostatic proteinuria can be diagnosed more accurately.