Ionized hypercalcemia in 238 cats from a referral hospital population (2009-2019)

Abstract

Background: Ionized calcium concentration ([iCa]) is more sensitive for detecting calcium disturbances than serum total calcium concentration but literature on ionized hypercalcemia in cats is limited. Urolithiasis is a possible adverse consequence of hypercalcemia.

Hypothesis/objectives: To describe clinical details of diagnoses associated with ionized hypercalcemia in cats and association with urolithiasis.

Animals: Cats (238) seen between 2009 and 2019 at a referral hospital with [iCa] above the normal reference interval.

Methods: Observational cross-sectional study. Signalment, serum biochemical and imaging findings were reviewed for cats with ionized hypercalcemia considered to be clinically relevant (>1.41 mmol/L). Data were summarized by cause of hypercalcemia (i.e., diagnosis).

Results: Diagnoses for the 238 cats with [iCa] >1.41 mmol/L included: acute kidney injury (AKI; 13%), malignancy-associated (10.1%), idiopathic hypercalcemia (IHC; 10.1%), chronic kidney disease/renal diet-associated (8.4%), iatrogenic (5.5%), primary hyperparathyroidism (2.1%), vitamin D toxicity (2.1%) and granulomatous disease (1.7%). In 112 cases (47.1%), no cause for ionized hypercalcemia could be determined (n = 95), hypercalcemia was transient (n = 12), or the cat was juvenile (<1 year; n = 5). Urolithiasis was identified in 83.3% of AKI, 72.7% of iatrogenic, 61.1% of CKD/renal diet-associated and 50% of IHC cases that were imaged (<50% for other diagnoses). Diagnoses with a high proportion of concurrent total hypercalcemia included primary hyperparathyroidism (100%), vitamin D toxicity (100%), malignancy-associated (71.4%), granulomatous disease (66.7%) and IHC (65.2%).

Conclusions and clinical importance: Ionized hypercalcemia was most commonly associated with kidney diseases, neoplasia or IHC. The proportion of urolithiasis cases varied by diagnosis.

Keywords: AKI; calcium; cat; idiopathic; kidney stone.

FIGURE 1

Box and whisker plot (via the Tukey method) of the first high ionized calcium (A) and maximum ionized calcium (B) results from 238 cats with at least 1 ionized calcium >1.41 mmol/L, separated by final diagnosis. The box represents the 25th, median and 75th percentiles, the upper whisker represents the highest data point within 1.5× the interquartile range and the lower whisker represents the lowest data point within 1.5× the interquartile range. Any outliers are plotted individually. CKD, chronic kidney disease; iCa, ionized calcium

FIGURE 2

First high ionized calcium concentration and serum total calcium concentration for 128 cats with an ionized calcium >1.41 mmol/L at some point during their investigations, a cause identified for their hypercalcemia, and a serum total calcium concentration measured at the Royal Veterinary College diagnostic laboratory. The dashed line on the X‐axis represents the upper limit of the reference range for serum total calcium concentration (11.6 mg/dL). CKD, chronic kidney disease; iCa, ionized calcium

FIGURE 3

Urolithiasis identified on abdominal imaging in 176 cats with clinically relevant ionized hypercalcemia, by diagnosis. The length of the bar indicates the number of cats with each diagnosis undergoing abdominal imaging, separated by the findings in relation to urolithiasis. CKD, chronic kidney disease