Parathyroid Hormone (PTH)

Clinical Chemistry

---

Description

PTH is a peptide hormone which is involved in calcium, vitamin D and phosphate homeostasis. PTH is released from the parathyroid gland in response to low calcium. The actions of PTH are: 1. Release of calcium from bone. 2. Increased renal tubular absorption of calcium. 3. Reduced renal tubular absorption of phosphate. 4. Stimulates the 1-alpha-hydroxylase enzyme to form more actived vitamin D which in turn increases absorption of calcium from the gut. Causes of high calcium with normal or high PTH: 1. Primary hyperparathyroidism. 2. Tertiary hyperparathyroidism. 3. Familial hypercalcaemic hypocalciuria. High calcium and low or undetectable PTH: 1. Malignancy ( most common cause ) 2. TB/sarcodiosis. 3. Drugs. Low calcium with high PTH: 1. Appropriate response to low calcium. 2. Vitamin D deficiency ( calcium may also be normal ). 3. End stage renal failure. Low calcium with low PTH: 1. Low magnesium ( Mg is required for PTH release ). 2. Hypoparathyroidism, eg following neck surgery.

---

Indications

1. Investigation of high calcium. 2. Investigation of low calcium. 3. Monitoring in patients with chronic kidney disease. 4. During selective venous sampling to identify source of increased PTH production. 5. Intra-operatively to assess completeness of parathyroidectomy.

---

Sample Type

Plasma. EDTA ( fill tube completely ). Also send a serum ( SST/Gel ) sample for calcium and albumin.

---

Reference Range

Reference ranges are provided on the report. Alternatively, please contact the laboratory for current ranges.

---

Turnaround Time

Within 1 day

---

Testing Frequency

As required

---

External Notes

For appropriate interpretation, requests for PTH should be accompanied by a serum sample for calcium and albumin.
PTH will not be measured on serum samples due to poor stability. PTH is stable in separated EDTA plasma for up to 72 hours at 2-8C (48 h at 15-25C).

PTH results are assay dependent. Monitoring of individual patients is therefore best done using one assay. The Roche assay uses antibodies against epitopes in the amino acid regions 26-32 (N-terminal) and 37-42 (C-terminal).

---

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.