Ionized calcium-to-phosphorus ratio predicts neoplasia in azotemic dogs: a retrospective study of 105 cases.

OBJECTIVE: To evaluate dogs with total hypercalcemia, azotemia, and normal serum phosphorus concentrations to determine whether a calcium-to-phosphorus ratio (Ca:P) or ionized Ca:P (iCa:P) could be utilized to predict underlying neoplasia. ANIMALS: 105 dogs were included in the study. Thirty-seven percent (n = 39) had known neoplasia, and 63% (66) had no evidence of neoplasia. PROCEDURES: A retrospective medical records search was performed. An observational cutoff of 2.5 for Ca:P and 0.33 for iCa:P was used for determining sensitivity and specificity between the neoplasia and nonneoplasia groups. RESULTS: Total hypercalcemia was higher in dogs with neoplasia compared to nonneoplastic cases of hypercalcemia. Ca:P of 2.5 had an 80% sensitivity and 46% specificity for predicting neoplasia. iCa:P of 0.33 had a 92% sensitivity and 77% specificity for predicting neoplasia in azotemic dogs. CLINICAL RELEVANCE: The sensitivity and specificity of Ca:P was low, making it an unreliable tool to predict neoplasia in this specific study population. However, iCa:P may have some usefulness in determining presence of neoplasia in patients with high calcium, azotemia, and normal phosphorus.