PTHrP

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	PTHrP
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Contents

Introduction, Pathophysiology, Clinical utility, Measurement at SydPath, Sample collection and handling, Charging

Introduction

Parathyroid hormone related peptide (PTHrP) is a protein produced by tumours which may lead to hypercalcaemia. The measurement of PTHrP can be of assistance in determining the cause of an otherwise unexplained hypercalcaemia.

Pathophysiology (top of page)

PTHrP is a protein secreted by some cancer cells leading to humeral hypercalcaemia of malignancy (HHM). PTHrP is produced commonly in patients with breast or prostate cancer and occasionally in patients with myeloma. PTHrP shares the same 13 N-terminal amino acids as parathyroid homone (PTH), however the size and remaining amino acids are quite distinct. PTHrP is larger than PTH and contains between 139 and 173 amino acids compared to 84 for PTH.

PTHrP shares many actions with PTH leading to increased calcium release from bone, reduced renal calcium excretion and reduced renal phosphate reabsorption. However PTHrP does not produce the normal anion gap metabolic acidosis commonly found with hyperparathyroidism.

PTHrP has important physiological roles in normal growth and development, particularly in the area of bone formation.

Clinical utility (top of page)

PTHrP measurement can assist with the identification of HHM. The usual pattern of HHM is elevated total and ionised calcium, low PTH (note that PTH may be within the lower section of the reference interval), and no other cause for the elevated calcium, eg exclusion of excessive vitamin D, sarcoid, TB and other causes. If the presence of a malignancy is uncertain, or there are several possible causes for the hypercalcaemia, measurement of PTHrP can be of assistance.

Measurement at SydPath (top of page)

PTHrP is measured at SydPath using a 2 site immuno-radiometric assay from Nichols Institute Diagnostics. The assay is performed approximately monthly depending on request numbers.

Reference Interval: < 1.3 pmol/L

Sample collection and handling (top of page)

Tubes: A commercial protease inhibitor cocktail tube is recommended (PTHrP cocktail tube, cat #38-2182, Immunodiagnostics, Ph: (02) 9515-9300). An EDTA tube with aprotinin (Trasylol) added at 0.4 TIU (Trypsin Inhibitory Units) or 1000 KIU (Kallekrin Inhibitory Units) per mL of sample is also acceptable.

PTHrP is highly labile and care is required to ensure an accurate result is obtained.

The collection tube must be cooled prior to collection of the sample. And kept on-ice until centrifugation.

Centrifugation should be performed as soon as possible in a refrigerated centrifuge.

For outside laboratories please freeze the plasma immediately after separation and transport to SydPath frozen. Repeated freeze/thawing should be avoided.

Charging:

The cost of PTHrP measurement is not covered by the Health Insurance Commission. SydPath provide this test free of charge to patients within NSW. For samples referred from interstate or overseas the PTH rP will be billed at the same cost as a PTH assay ($29.80). For any queries please contact Dr Graham Jones or Lyn Boscato (02 8382-9100).

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For further information please contact Dr Graham Jones on 8382-9100

gjones@stvincents.com.au

Last updated 11/2/02