Parathyroid hormone (PTH)

Chemical Pathology

Notes

Parathyroid hormone (PTH) is secreted by the parathyroid glands and plays an important role in calcium homeostasis.
PTH analysis is used in the investigation of abnormal calcium levels, to distinguish between parathyroid and non-parathyroid causes; in monitoring renal patients and in assessing patients immediately post parathyroidectomy (or thyroidectomy).
As PTH changes rapidly in response to calcium levels and is also cleared from the blood very quickly (half-life approximately 5 minutes) it is essential to always interpret PTH levels in conjunction with the calcium level. Requests for PTH should therefore always be accompanied by a request for a simultaneous calcium level.
The local PTH assay measures intact PTH molecule 1-84 amino acids).

PTH can be assayed during a parathyroidectomy on an urgent basis (i.e. intra-operative PTH levels) however this must be booked with the laboratory at least a week in advance. Please contact the duty biochemist for further details if access to this service is required.

Sample requirements

If patient on high dose biotin therapy (>5mg/day) collect sample at least 8 hours after the last dose.
Two different sample tube types are required, an EDTA sample for PTH and a plain serum sample for simultaneous calcium.
Draw Gold/RUST top tubes first as EDTA contamination will cause falsely low calcium levels; (please note that if no gold top tube is sent for calcium then PTH will not be assayed.

For adults use a 4mL EDTA tube plus a 5mL gold top gel tube (or rust top for the Acute Unit)