Veterinarian School of Veterinary Medicine and Animal Science, University of Sao Paulo São Paulo, Sao Paulo, Brazil
Abstract: Background - Urinary calcium, magnesium, and phosphorus evaluation may be useful in diagnosing urinary tract disorders. However, to the best of our knowledge, validation of the colorimetric assay is not currently available. Objective – To validate a colorimetric method for measuring urinary calcium, magnesium and phosphorus in dogs. Animals – Urine samples of dogs treated at the Veterinary Teaching Hospital of the University of Sao Paulo. Samples with color abnormalities or cloudiness were excluded. Methods – Samples were stored at -80ºC, thawed, pooled, then acidified (AC) with 10 µl of 10% nitric (calcium; magnesium) or hydrochloric acid (phosphorus) per 1 ml of urine; or kept non-acidified (NA). Ten measurements were performed daily over five consecutive days using an automatic biochemistry analyzer. Results – All protocols showed satisfactory coefficients of variation (< 10%): NA calcium (0.69%, 2.02%, 3.31%, 2.83%, 2.07%), magnesium (1.11%; 1.06%; 1.01%; 1.22%; 0.55%), phosphorus (1.92%; 3.34%; 2.42%; 1.19%; 1.51%); AC calcium (1.49%, 1.22%, 1.44%, 1.72%, 3.86%), magnesium (4.59%; 0.92%; 0.98%; 0.72%; 1.00%), phosphorus (2.05%; 1.91%; 2.33%; 2.87%; 2.67%). Inter-assay analysis revealed differences across days in all subgroups: NA and AC calcium (p < 0.0001); NA and AC magnesium (p < 0.0001); NA and AC phosphorus (p < 0.001). Conclusions and clinical importance – AC and NA samples may be used to measure urinary calcium, magnesium and phosphorus by the colorimetric method in dogs. This method is inexpensive and widely used, which may facilitate dissemination of urinary electrolyte assessment as a diagnostic and therapeutic monitoring tool.
