Veterinary School of Veterinary Medicine and Animal Science, University of Sao Paulo, São Paulo, Sao Paulo, Brazil
Abstract: Background – The measurement of electrolytes in urine may be useful in the diagnosis and management of urolithiasis or tubular disorders, however a validation study in cats is needed. Objective – To validate a colorimetric method for measuring urinary calcium and magnesium concentrations in cats. Animals – Urine samples of cats treated at the Veterinary Teaching Hospital of the University of Sao Paulo. Methods – Urine samples were stored at -80ºC. After thawing, samples were pooled (50 mL), and an Acidified Solution (AS; 1 mL urine:10 µL of 10% nitric acid) and a Non-Acidified Solution (NAS) were prepared. Ten consecutive measurements of calcium and magnesium were performed for intra-assay; measurements along five consecutive days were performed for inter-assay. Coefficient of variation (CV) < 10% was considered satisfactory. Results – Inter-assay CVs were: NAS magnesium (16,53%; 3,73%; 1,72%; 1,73% 1,29%), AS magnesium (2,63%, 1,69%, 2,42%, 1,90%, 2,40%), NAS calcium (6,92%; 1,79%; 4,72%; 2,61%; 2,65%) and AS calcium (1,81%; 2,30%; 2,46%; 1,67%; 1,40%). Differences were found in the intra-assay of magnesium using AS (P< 0.05). There were no differences in the inter-assay of urinary magnesium between AS and NAS. Regarding urinary calcium, differences were found in the inter-assay between AS and NAS (P< 0.0001). Conclusions and clinical importance – Urinary calcium measurement should be performed in acidified samples, and magnesium measurement in non-acidified samples. The colorimetric method is inexpensive and widely used, which may support the use of urinary electrolyte evaluation as a diagnostic and therapeutic monitoring tool.
