PTH-related protein (PTHrP) in dogs and cats
Parathyroid hormone-related protein (PTHrP) acts on the same receptors as parathyroid hormone and raises blood calcium. In a healthy animal it plays no part in everyday calcium control, but some tumours release it into the blood. It is a specialised test, ordered when calcium is high and the cause is not yet clear.
What it shows
PTHrP is made by several kinds of cells in the body, the kidney among them, but in a healthy animal it is not involved in keeping calcium steady. Its effect is similar to that of parathyroid hormone (PTH): it binds the same receptors, frees calcium from bone and makes the kidneys keep calcium and lose phosphate. The result is higher total and ionized calcium and, often, lower phosphate.
Some tumours produce PTHrP in large amounts. This is called humoral hypercalcaemia of malignancy — “humoral” means the tumour acts at a distance through the blood rather than by growing into bone. PTHrP is a hormone-like protein that can cause this kind of high calcium, and that is why the test exists.
Higher than reference — what it may be a sign of
- Cancer-related high calcium. A high PTHrP together with high ionized calcium and a low PTH supports the picture of humoral hypercalcaemia of malignancy. Tumours linked to it in dogs include lymphoma and apocrine gland adenocarcinoma of the anal sac; thymoma, various carcinomas and multiple myeloma have also been reported. The result points the vet towards a search — the tumour itself is found by examination, imaging and cell or tissue samples, not by this number.
- Granulomatous (inflammatory) disease. Long-standing inflammation, for example some fungal infections, can raise calcium too. Macrophages in such lesions can make PTHrP, and in published tables of laboratory findings PTHrP is listed there as normal or raised.
A raised PTHrP is a sign, not a diagnosis. It only means something next to ionized calcium and PTH measured at the same time.
Lower than reference
PTHrP is expected to be high only in cancer-related high calcium, so a result inside the range or below detection is the usual finding otherwise. It is also what is expected in primary hyperparathyroidism and in idiopathic hypercalcaemia of cats. Important: a normal or negative PTHrP does not rule out cancer. Tumours can raise calcium in other ways — through vitamin D metabolites, cytokines or by destroying bone.
A falsely low result can come from the sample. In one laboratory’s experience, PTHrP was undetectable in about half of serum samples whose paired EDTA plasma showed raised values, most likely because the protein had broken down. PTHrP is also more sensitive to warm transport than PTH. A negative result can still be a true negative.
Look at together with
- Ionized calcium (see calcium) — PTHrP is read only against it.
- PTH — low PTH with high calcium points outside the parathyroid glands; normal or high PTH with high calcium points to the glands themselves.
- Phosphorus — often normal, sometimes low when high calcium is driven by PTHrP.
- 25-hydroxyvitamin D and calcitriol — to check whether vitamin D explains the high calcium instead.
Units and conversion
PTHrP is reported in pmol/L, and there is no second unit to convert. In the app each row keeps the unit printed on the form, so results from different dates line up on one chart.
Reference range
The reference range is on your lab’s form. For PTHrP the value is read as part of a set: ionized calcium, PTH and PTHrP from the same sample, often offered together as a “malignancy profile”. Few laboratories measure PTHrP for animals: in 2026 a US veterinary laboratory that believes it is the only veterinary lab offering the test paused it because of reagent supply problems, noting that the test is mostly run by human laboratories. A vet may therefore order PTH and ionized calcium without PTHrP.
Cats and dogs
High calcium is uncommon in cats, and it is most often idiopathic — with PTHrP normal. Among tumours, lymphoma and squamous cell carcinoma are named as the commonest causes of cancer-related high calcium in cats; raised PTHrP has been reported with carcinomas of the lung, kidney and thyroid, osteosarcoma and occasionally lymphoma.
In dogs, cancer is the most common cause of persistent high calcium, with T-cell lymphoma first and anal sac adenocarcinoma second. This is why PTHrP is usually ordered for a dog with high ionized calcium and a low PTH. High calcium has also been described with histiocytic sarcoma, more often in Bernese Mountain Dogs than in Flat-coated Retrievers.
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.
Sources
- Michigan State University Veterinary Diagnostic Laboratory. Endocrinology — Calcium Disorders.
- Michigan State University Veterinary Diagnostic Laboratory. Endocrinology Sample Too Warm.
- Michigan State University Veterinary Diagnostic Laboratory. Extended Unavailability of PTHrP and Malignancy Profile (news, 2026).
- eClinPath (Cornell University College of Veterinary Medicine). Calcium — chemistry / minerals.
- eClinPath (Cornell University College of Veterinary Medicine). Minerals: overview (calcium, phosphate and their hormones).
- Ham K. Hypercalcemia in Dogs and Cats. Merck Veterinary Manual, professional version, full review June 2023.
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.