If ionised calcium is also requested, keep ionised calcium sample COLD AFTER COLLECTION AND DURING TRANSPORT to laboratory (fridge/cold pack). The PTH sample may also be kept cold (after centrifugation) with the ionised calcium to keep specimens together. Send to arrive in laboratory within 7 hours of collection to allow for processing within 8 hours of collection.
GENERAL NOTES
It is essential that blood is collected for calcium at the same time as for parathyroid hormone (PTH) so that results can be interpreted.
APPLICATION: Investigation of unexplained hypercalcaemia or hypocalcaemia.
INTERPRETATION: The interpretation of PTH levels is dependent on the patient's corrected calcium or ionised calcium at the time the blood specimen was taken. In hyperparathyroidism, the PTH level is increased or high-normal in the presence of hypercalcaemia. In most cases of hypercalcaemia associated with malignancy, PTH level will be suppressed, with an elevated PTHrP. Hypoparathyroidism is associated with a low PTH. Pseudohypoparathyroidism and other causes of hypocalcaemia are associated with a high PTH. See also PTH related protein (PTHrP).
