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Hypercalcemia: causes of high calcium, and low calcium

Hypercalcemia in a dog or cat is best confirmed with ionized calcium, because total calcium often misclassifies calcium status, and the most likely causes differ between the two species.

Reviewed by Brian Toncray, DVM · October 22, 2026

Ionized calcium is the biologically active fraction, and total calcium does not predict it reliably in many clinical conditions¹. In dogs with a confirmed ionized hypercalcemia, total and albumin-corrected calcium did not reflect calcium status accurately². Start with the right measurement and the cause list becomes much more useful.

Ionized calcium

High can mean: In dogs, neoplasia is the most common cause, with lymphoma first. In a series of dogs with ionized hypercalcemia, kidney failure, primary hyperparathyroidism and hypoadrenocorticism followed in that order; dogs with lymphoma or anal sac adenocarcinoma ran higher values, but the size of the rise did not predict the cause². A later review ranks primary hyperparathyroidism ahead of chronic kidney disease³. Canine lymphoma can produce parathyroid hormone-related protein⁴. Vitamin D intoxication, including cholecalciferol rodenticide ingestion, belongs on the list and can cause vomiting, anorexia and polyuria with polydipsia⁵. In cats, idiopathic hypercalcemia is the most common cause, followed by chronic kidney disease and then neoplasia³; in an older feline series, lymphoma and squamous cell carcinoma were the commonest tumors and calcium oxalate uroliths were frequent⁶.
Low can mean: Puerperal tetany (eclampsia) in the lactating bitch and queen⁷, and critical illness: in hypoalbuminemic dogs in intensive care, close to a third were ionized hypocalcemic at admission⁸.
Can shift it artificially: Sample handling. Anaerobic measurement under controlled conditions is the most reliable; aerobic measurement with species-specific pH correction correlates well with it¹.
Next test: For confirmed hypercalcemia in a dog: lymph node palpation and a rectal examination for an anal sac mass, imaging, then parathyroid hormone and parathyroid hormone-related protein as the cause list dictates^2,3. In a cat, the same screen with idiopathic disease kept in mind³.

Total calcium

High can mean: A prompt to measure ionized calcium. It does not by itself establish hypercalcemia^2,1.
Low can mean: Often hypoalbuminemia rather than a true ionized deficit. In critically ill hypoalbuminemic dogs, a low total calcium caught every ionized hypocalcemia but overcalled it in many dogs that were normocalcemic⁸.
Can shift it artificially: Protein binding. Because much of total calcium is bound to albumin, changes in albumin move the total without changing the active fraction¹.
Next test: Ionized calcium whenever total calcium is outside the interval in a sick patient⁸.

Albumin-adjusted calcium

High can mean: Not a substitute for ionized calcium when hypercalcemia is suspected².
Low can mean: Results are mixed. In critically ill hypoalbuminemic dogs, adjusted values misclassified calcium status in roughly two of every three dogs⁸. In a larger study limited to hypoalbuminemic dogs without high phosphorus, a low adjusted calcium was useful for detecting ionized hypocalcemia and a normal one made moderate ionized hypocalcemia unlikely⁹.
Can shift it artificially: High phosphorus and critical illness undermine the adjustment^9,8.
Next test: Measure ionized calcium directly when the answer changes management¹.

Phosphorus alongside calcium

High can mean: Kidney involvement. Among 71 cats with a high calcium, the ones whose underlying problem was renal failure ran a higher phosphorus than the ones with a tumor, which makes phosphorus a cheap pointer between those two branches⁶.
Low can mean: A low or low-normal phosphorus beside hypercalcemia fits a parathyroid hormone or parathyroid hormone-related protein driven process, as in primary hyperparathyroidism or humoral hypercalcemia of malignancy, provided kidney function is preserved.
Can shift it artificially: Read both values from the same sample.
Next test: Creatinine and urine specific gravity to judge the kidney's part in the picture⁶.

Reading these values together

In a dog with a confirmed ionized hypercalcemia, think neoplasia first and look for it physically before reaching for the hormone panel: lymph nodes, the anal sacs, the chest and the abdomen². Primary hyperparathyroidism, kidney disease and hypoadrenocorticism follow, in an order that differs between sources^2,3.

Cats reverse part of the order. Idiopathic hypercalcemia leads, chronic kidney disease follows and neoplasia comes third³, and a cat with hypercalcemia and calcium oxalate uroliths is a recognized combination⁶. In any species, a low total calcium in a hypoalbuminemic patient is not treated until the ionized value confirms it⁸.

Low ionized calcium has its own short list in practice. A lactating bitch or queen that is restless, trembling or stiff needs an ionized calcium before anything else, because puerperal tetany is a reproductive emergency⁷. In the intensive care unit, ionized hypocalcemia is common enough in hypoalbuminemic dogs that the authors of one study recommended checking ionized calcium in every such patient whose total calcium is low⁸. Neither situation is one where an albumin correction should stand in for the direct measurement.

Example: a panel worked through

Example. A 9-year-old neutered male dog is drinking and urinating more. Total calcium is above the lab's interval and ionized calcium confirms it. Phosphorus is at the low end of its interval, creatinine is within its interval and the urine is poorly concentrated.

Ionized hypercalcemia in a dog puts neoplasia first, with lymphoma and anal sac adenocarcinoma the tumors to hunt². Peripheral lymph nodes are palpated, a rectal examination checks the anal sacs, and the chest and abdomen are imaged. Parathyroid hormone and parathyroid hormone-related protein follow if the search is empty, with the owner asked about rodenticides in the house^3,5.

Frequently asked questions

What are the causes of high calcium in a dog?

Neoplasia, led by lymphoma, then primary hyperparathyroidism, kidney disease and hypoadrenocorticism, whose order varies between sources, with vitamin D intoxication also on the list^2,3,5.

Is high calcium in a cat usually cancer?

No. Idiopathic hypercalcemia is the most common cause in cats, followed by chronic kidney disease and then neoplasia³.

Should I rely on total calcium?

No. Total calcium often misclassifies calcium status; measure ionized calcium to confirm a high or low result^1,2.

Can I correct calcium for albumin?

With caution. Adjusted values performed poorly in critically ill dogs, though a low adjusted value was useful in hypoalbuminemic dogs without high phosphorus^8,9.

Sources

Schenck PA, Chew DJ. Calcium: total or ionized?. Vet Clin North Am Small Anim Pract. 2008; 38(3):497-502, ix. PMID: 18402876. DOI: 10.1016/j.cvsm.2008.01.010.
Messinger JS, Windham WR, Ward CR. Ionized hypercalcemia in dogs: a retrospective study of 109 cases (1998-2003). J Vet Intern Med. 2009; 23(3):514-9. PMID: 19658207. DOI: 10.1111/j.1939-1676.2009.0288.x.
de Brito Galvão JF, Schenck PA, Chew DJ. A Quick Reference on Hypercalcemia. Vet Clin North Am Small Anim Pract. 2017; 47(2):241-248. PMID: 28012787. DOI: 10.1016/j.cvsm.2016.10.016.
Kubota A, Kano R, Mizuno T, et al. Parathyroid hormone-related protein (PTHrP) produced by dog lymphoma cells. J Vet Med Sci. 2002; 64(9):835-7. PMID: 12399610. DOI: 10.1292/jvms.64.835.
Gerhard C, Jaffey JA. Persistent Increase in Serum 25-Hydroxyvitamin D Concentration in a Dog Following Cholecalciferol Intoxication. Front Vet Sci. 2019; 6:472. PMID: 31998760. DOI: 10.3389/fvets.2019.00472.
Savary KC, Price GS, Vaden SL. Hypercalcemia in cats: a retrospective study of 71 cases (1991-1997). J Vet Intern Med. 2000; 14(2):184-9. PMID: 10772491. DOI: 10.1892/0891-6640(2000)014<0184:hicars>2.3.co;2.
Davidson AP. Reproductive causes of hypocalcemia. Top Companion Anim Med. 2012; 27(4):165-6. PMID: 23415384. DOI: 10.1053/j.tcam.2012.09.002.
Sharp CR, Kerl ME, Mann FA. A comparison of total calcium, corrected calcium, and ionized calcium concentrations as indicators of calcium homeostasis among hypoalbuminemic dogs requiring intensive care. J Vet Emerg Crit Care (San Antonio). 2009; 19(6):571-8. PMID: 20017763. DOI: 10.1111/j.1476-4431.2009.00485.x.
De Witte F, Klag A, Chapman P. Adjusted calcium concentration as a predictor of ionized hypocalcemia in hypoalbuminemic dogs. J Vet Intern Med. 2021; 35(5):2249-2255. PMID: 34424577. DOI: 10.1111/jvim.16247.