210 dogs with naturally occurring primary hyperparathyroidism (PHPTH) and 200 randomly selected, age-matched control were studied. Medical records of affected dogs were reviewed for signalment: clinical features, and results of clinicopathologic testing, serum parathyroid hormone assays, and diagnostic imaging.

Mean age of the dogs with PHPTH was 11.2 yrs (range, 6–17 yrs). The most common clinical signs were attributable to urolithiasis (65, 31%) or urinary tract infection (61, 29%); i.e., straining to urinate, increased frequency of urination, and hematuria. Most dogs (149, 71%) did not have any observable abnormalities on physical examination. All affected dogs had hypercalcemia, and most (136, 65%) had hypophosphatemia. Overall, 200 of the 210 (95%) dogs had BUN and serum creatinine concentrations within or less than the reference range, and serum parathyroid hormone concentration was within reference limits in 135 of 185 (73%) dogs in which it was measured. Results suggested that urolithiasis and urinary tract infection may be associated with hypercalcemia in dogs with primary hyperparathyroidism, but that development of renal insufficiency is uncommon (Feldman, Hoar, et al. J Am Vet Med Assoc, 227:756-761, 2005).

1,633 canine serum samples were analyzed to determine whether total serum calcium (tCa) or adjusted tCa concentrations accurately predict ionized calcium (iCa) status in dogs.

The tCa concentration was adjusted for total protein (TP) or albumin concentration by use of published equations. Correlations between iCa and tCa or adjusted tCa, tCa and TP, and tCa and albumin were calculated. Diagnostic discordance was 27% when tCa concentration was used to predict iCa status. Diagnostic discordance in predicting iCa was also determined for 490 dogs with chronic renal failure (CRF) and was found in ~37% of them. Positive predictive value and positive diagnostic likelihood ratios were poor when tCa concentration was used to predict iCa status. The tCa concentration overestimated normocalcemia and underestimated hypocalcemia. Adjusted tCa overestimated hypercalcemia and underestimated hypocalcemia.

The study concluded that neither tCa nor adjusted tCa concentrations are acceptable for predicting iCa status in dogs. Thus, use of adjustment equations is not recommended, as predicting iCa status by this means could cause serious mistakes in diagnosis and case management, especially in dogs with CRF. Direct measurement of iCa concentration is necessary for accurate assessment of calcium status (Schenck, Chew, Am J Vet Res, 66:1330-1336, 2005).