PARATHYROID HORMONE (PTH) AND IONISED CALCIUM (iCa) ASSAYS
Combination of PTH and iCa measurements can help distinguish between:
- PRIMARY HYPERPARATHYROIDISM (parathyroid dependent hypercalcaemia) – functional parathyroid neoplasia.
- PARATHYROID SUPPRESSION (parathyroid independent hypercalcaemia) – hypercalcaemia of malignancy, vitamin D toxicosis (cholecalciferol rodenticide), feline idiopathic hypercalcaemia.
- PRIMARY HYPOPARATHYROIDISM (parathyroid dependent hypocalcaemia) – parathyroid destruction by inflammation or surgery.
- SECONDARY HYPERPARATHYROIDISM (parathyroid independent hypocalcaemia) – renal failure, calcium losses (eg pancreatitis), dietary deficiency, hyperadrenocorticism, hyperthyroidism.
SAMPLE REQUIREMENTS FOR PARATHYROID HORMONE ASSAY
This test requires at least 1ml EDTA plasma collected on ice and rapidly frozen.
- Place the blood sample into a cooled plastic (NOT glass) EDTA tube kept on ice.
- Mix well but gently and centrifuge as quickly as possible – ideally in a refrigerated centrifuge.
- Transfer the plasma supernatant into a cooled plastic (NOT glass) PLAIN tube kept on ice.
- LABEL “PTH” and freeze the EDTA plasma sample immediately and KEEP FROZEN OVERNIGHT before collection by the BattLab courier who will bring a transport freezer pack – please call the lab to let us know this is a sample requiring special handling.
SAMPLE REQUIREMENTS FOR IONISED CALCIUM ASSAY
This test requires at least 200ul of separated serum collected under anaerobic conditions.
- Collect the blood into serum tubes (gel barrier tubes must NOT be used) and ensure that each tube is 100% full – when screwing the lid down, avoid the inclusion of any air bubbles which will destroy the ionised calcium.
- Allow 15 minutes for the blood to clot and then centrifuge at 7,500 g for 5 minutes. Remove the serum and place into another plain tube which must be 100% filled and airtight – ie containing no air bubbles at all.
- LABEL “CALCIUM” and REFRIGERATE (DO NOT FREEZE) the anaerobic serum sample before collection by the BattLab courier – please call the lab to let us know this is a sample requiring special handling.