You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Hyperparathyroidism is common in renal failure in cats and dogs, but it is rarely looked for by clinicians. Diagnostic tests are available that help to determine baseline levels at the time of presentation, and sequential tests can be used to assess response to treatment.

In renal failure parathyroid hormone (PTH) concentrations increase in response to low blood ionised calcium concentrations, and the threshold of blood calcium concentration required to stimulate parathyroid hormone secretion seems to be higher in renal failure patients. Finding a blood calcium concentration within the normal range does not mean that parathyroid hormone concentrations will be normal in that patient.

The Intact PTH immunoradiometric assay (Nichols Institute Diagnostics, USA) has been validated for use in dogs and cats. Animals should be fasted and rested overnight and samples are best collected mid-morning because PTH secretion is maximum at that time. Samples of 2ml blood in EDTA or heparin should be tested as soon as possible - within 30 minutes of collection. Samples can be transported to a remote diagnostic laboratory provided they are frozen.

In renal failure patients parathyroid hormone secretion will be greatly increased if dietary phosphate intake is high, so renal diets containing controlled amounts of phosphate should be provided. If very high PTH concentrations are present additional therapeutic strategies might include the use of phosphate-binders and vitamin D supplementation.

True ionised hypercalcaemia (ie high ionised calcium concentrations not high total calcium concentrations) is rare and if it occurs malignant cancer and primary hyperparathyroidism should be considered in the differential diagnosis. PTH concentrations need to be assessed in conjunction with calcium and phosphate and azotaemia :

 

Disease	PTH	Ionised Ca	Phosphate	Azotaemia
Renal Failure	High	Low	Normal/High	Yes
Malignancy	Low	High	Normal	No initially - yes later
Primary Hyperparathyroidism	High	High	Low usually	No initially - yes later
Glucocorticoid administration OR Cushings disease	High	Normal/high	Normal/high	No

In elderly patients the possibility of concurrent diseases eg malignancy and renal failure can greatly confuse the interpretation of laboratory results.

Last updated : January 2016