Veterinary Calcium / Phosphorus Reference & Interpretation
Calcium, phosphorus and PTH reference ranges for dogs and cats, plus interpretation of hyper- and hypo-calcaemia patterns.
Normal ranges (dog & cat)
| Parameter | Dog | Cat | Units |
|---|---|---|---|
| Total calcium | 8.6–11.8 | 8.0–11.8 | mg/dL |
| Ionised calcium | 1.18–1.40 | 1.20–1.40 | mmol/L |
| Phosphorus (adult) | 2.5–6.8 | 3.0–7.5 | mg/dL |
| Phosphorus (puppy/kitten) Growth-related; not pathologic. | up to 9.5 | up to 8.5 | mg/dL |
| PTH | 0.5–5.8 | < 4.0 | pmol/L |
| Calcium × phosphorus product > 70 = risk of soft-tissue mineralisation. | < 70 | < 70 | mg²/dL² |
Interpreting hypercalcaemia
| Pattern | Differential |
|---|---|
| High Ca, high PTH | Primary hyperparathyroidism |
| High Ca, low PTH, low P | Humoral hypercalcaemia of malignancy (PTHrP+, e.g. lymphoma, anal sac adenocarcinoma) |
| High Ca, low PTH, normal/high P | Vitamin D toxicosis, chronic granulomatous disease |
| High Ca, low PTH, low ionised Ca | Total Ca elevation from hyperalbuminaemia, lipaemia (artefactual) |
Interpreting hypocalcaemia
| Pattern | Differential |
|---|---|
| Low ionised Ca | Hypoparathyroidism, ethylene glycol toxicity, eclampsia, severe pancreatitis, CKD |
| Low total Ca, normal ionised Ca | Hypoalbuminaemia (correct Ca for albumin) |
Always confirm an unexpected total calcium with ionised calcium - protein-bound calcium can shift the total without changing the physiologically active fraction. Lipaemia and haemolysis cause spurious elevations.
Frequently asked questions
Total calcium vs ionised calcium - which should I trust?
Ionised calcium is the biologically active form and the more accurate measurement. Total calcium is affected by albumin and pH; if total is borderline, always confirm with iCa before treating.
What are the top differentials for hypercalcaemia in dogs?
Mnemonic GOSHDARNIT: Granulomatous disease, Osteolysis (metastatic disease), Spurious, Hyperparathyroidism (primary), D-vitamin toxicity, Addison's, Renal failure, Neoplasia (lymphoma, anal gland adenocarcinoma), Idiopathic, Temperature (juvenile bone growth).
When is acute calcium gluconate indicated for hypocalcaemia?
Symptomatic patient with iCa < 0.8 mmol/L (~3.2 mg/dL total). 10% calcium gluconate 0.5-1.5 mL/kg slow IV over 10-20 minutes with cardiac monitoring. Stop if bradycardia or arrhythmia develops.