Asma Shaukat, Samina Ghayur, Farooq Ahmad Khan.
Stability of PTH with regard to storage temperature, duration and preservative.
Pak J Pathol Jan ;9(2):23-4.

Parathormone (PTH) is very unstable in serum. Various immunoassays are available for assessment of PTH. The assays for immunoreactive PTH (IPTH) is considered to be more reliable for diagnosis than those directed against C-or N-terminal. Preanalytical exposure to ambient temperature (temp) for a considerable time may cause degradation of PTH as it is very thermolabile. We studied the stability of PTH with regard to storage temperature, duration and added preservative for performing iPTH assay. Venous blood was collected in chilled tubes (5 ml each in plain and aprotinin containing tubes) from 18 individuals (aged 20-50 years) at 0700-1000h with overnight fast. Serum obtained was analysed for PTH (zero time value) and divided into 6 aliquots (3 with and 3 without aprotinin). Two aliquots (one each with and without aprotinin) were kept at room temperature (RT); 2 at 4°C and 2 at -20°C. PTH was measured after 24h and 72h and was compared to the zero time value of PTH. Significant decline in PTH was seen when the samples were stored at RT for 72h. This effect was abolished when aprotinin (protease inhibitor) was added to the samples. No significant difference from zero time value was noticed in the aprotinin treated or untreated sera kept at 4°C or -20°C for 72h. Thus proper storage and addition of aprotinin may significantly reduce PTH degradation.

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