Chest radiographs looking for any nodular lesions, cranial mediastinal masses or lytic lesions in the dorsal spinous processes or ribs are also part of the workup. Abdominal ultrasound will be useful if trying to rule out a neoplastic process. Cystic calculi also may be seen in these patients due to the formation of calcium oxalate stones.

Serum samples for PTH measurement should be sent frozen to the lab to prevent degradation. Intact PTH is measured by RIA and has been validated for use in both feline and canine patients. PTH levels should be assessed relative to a simultaneous measurement of iCa.

Ionized calcium levels need to be collected anaerobically, as changes in the pH will artifactually decrease iCa levels. In addition, serum separator tubes (SST) should be avoided, as they can artifactually increase the iCa.

To minimize any contact with air, serum for iCa measurement should be drawn directly into a vacutainer tube. Blood should be allowed to clot and then separated by centrifugation. Serum should be removed without removing the red top and transferred to a second unopened red top vacutainer.

This hormone acts as a PTH-like factor and plays a central role in the development of humoral hypercalcemia of malignancy. It shares 70% sequence homology with PTH and has been isolated from certain neoplasms such as lymphoma and apocrine gland adenocarcinoma. In hypercalcemic patients with these malignancies, PTHrp will be elevated while PTH level will be decreased.

This test will require fresh or frozen EDTA plasma as serum can give false negative results.

References: Ettinger and Feldman, Textbook of Veterinary Internal Medicine, 6th Ed, Ch. XVI, 2005.