Calcium (total, ionized, corrected) in cats and dogs

Calcium in the blood exists in three forms, and a routine panel measures all of them together as total calcium. The ionized part is the one cells actually use; it is measured separately. The two can disagree, so when a calcium problem is suspected, vets rely on ionized calcium.

SectionBiochemistry

SampleBlood (serum or plasma); ionized calcium — serum or heparin plasma handled without air

Unitsmmol/L · 1 mg/dL = 0.2495 mmol/L

On formsCa, iCa, Ca2+

What it shows

According to eClinPath, about 50–55% of total calcium is free ionized calcium, 35–45% is bound to proteins (mostly albumin) and 5–10% is bound to small anions such as citrate or phosphate. Hormones that keep calcium stable react only to the ionized part.

Because so much calcium rides on albumin, low albumin lowers total calcium without touching the active part — eClinPath calls it the most common cause of low total calcium. For dogs there is a formula that “corrects” total calcium for albumin, and some forms print this corrected calcium. The sources are sceptical: eClinPath does not recommend these formulas, and the Merck Veterinary Manual states that total and adjusted total calcium are not reliable measures of calcium status in dogs and cats. When it matters, ionized calcium is measured directly.

Higher than reference — what it may be a sign of

Cancer (humoral hypercalcemia of malignancy) — Merck names it the most common cause in dogs.
Primary hyperparathyroidism — an overactive parathyroid gland.
Too much vitamin D: cholecalciferol rodenticides, excess supplements, some plants.
Addison’s disease — Merck notes the rise is usually transient and ionized calcium is usually normal.
Kidney disease — total calcium can be high while ionized calcium is normal or low.
Idiopathic hypercalcemia in cats.
Non-disease reasons: dehydration, young age, lipemia of the sample.

Lower than reference

Low total calcium most often follows low albumin. Other causes include kidney disease, pancreatitis, antifreeze (ethylene glycol) poisoning, eclampsia around birth and nursing, and an underactive parathyroid gland. eClinPath adds that cats with a urethral blockage or hyperthyroidism can have low ionized calcium with normal total calcium. An extremely low result can be an artefact: EDTA from a purple-top tube binds calcium, and IDEXX lists falsely low calcium among the effects of EDTA contamination.

Look at together with

Albumin — the first thing to check when total calcium is low.
Phosphorus — high calcium with low phosphorus is typical of primary hyperparathyroidism; both high suggests kidney disease or vitamin D excess.
Creatinine and urea — kidney function changes how calcium is handled.
Magnesium — eClinPath advises measuring it when low calcium has no clear explanation.
Sodium and potassium — to look for Addison’s disease in a dog with high calcium.

Units and conversion

Calcium is reported in mg/dL (North America) or mmol/L (Europe). Multiply mg/dL by 0.2495 to get mmol/L: 10 mg/dL is about 2.5 mmol/L. Ionized and corrected calcium use the same units and the same factor; ionized calcium is often given in mmol/L. In the app each row keeps the unit printed on the form.

Reference range

The reference range is on your lab’s form. Ionized calcium has its own, much lower range — roughly half of total calcium is ionized — so never read it against the total calcium range. Ionized calcium is sensitive to handling: eClinPath warns that contact with air and freezing falsely lower it, while a sample left standing can falsely raise it. A single surprising value is usually rechecked, ideally as ionized calcium.

Cats and dogs

Cats

Merck calls idiopathic hypercalcemia the most common form of high calcium in cats; eClinPath notes that some of these cats also have calcium oxalate stones. Cancer also causes high calcium in cats, most often lymphoma and squamous cell carcinoma. In cats and dogs with chronic kidney disease total calcium is usually normal or low, and eClinPath advises blaming the kidneys for high calcium only after other causes are ruled out.

Dogs

In dogs, cancer is the leading cause of high calcium, most often lymphoma and anal sac adenocarcinoma. Primary hyperparathyroidism usually appears in dogs older than 7 years, and eClinPath names Keeshonds among predisposed breeds. Growing puppies can sit slightly above the adult range. In one study cited by eClinPath, only 9% of dogs with kidney disease and high total calcium had high ionized calcium.

In the app

Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.

Open the app

Sources

Updated 2 November 2026 · Mihail Ivanov, creator of Pet Tracker Space · Written with Claude and checked against the sources above.

This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.