Clin. Lab. 4/2014 689 Clin. Lab. 2014;60:689-692 ©Copyright SHORT COMMUNICATION Changes in Plasma Intact Parathyroid Hormone Levels Following 24-hour Incubation at Room Temperature as Determined by Roche Electrochemiluminescence PTH Immunoassay ASHUTOSH KUMAR ARYA AND NARESH SACHDEVA Department of Endocrinology, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India SUMMARY Background: Estimation of circulatory PTH is necessary for correct diagnosis of diseases related to the parathy- roid gland, bone, and kidney. Methods: Roche Electrochemiluminescence PTH immunoassay was used to measure changes in plasma iPTH con- centration in 100 random samples following a 24 hours incubation at room temperature. Results: Low to normal iPTH concentration individuals showed higher decrease in iPTH concentration as com- pared to individuals with elevated PTH and the rate of PTH degradation was significantly higher (p < 0.05) in the low to normal PTH group. Conclusions: Blood samples from suspected hypo- or normo-parathyroid subjects should be analyzed as soon as possible as a little degradation of PTH at room temperature could influence their clinical interpretation. (Clin. Lab. 2014;60:689-692. DOI: 10.7754/Clin.Lab.2013.130419) KEY WORDS intact parathyroid hormone, electrochemiluminescence immunoassay INTRODUCTION Parathyroid hormone (PTH) maintains calcium homeo- stasis mainly in bone and kidney and indirectly in the intestine. Estimation of circulatory PTH is necessary for correct diagnosis of diseases related to the parathyroid gland, bone and kidney as low PTH concentration is as- sociated with hypoparathyroidism while elevated PTH concentration is associated with diseases like hyperpara- thyroidism, chronic kidney disease, and renal osteodys- trophy [1]. In circulation, PTH is cleaved and metabo- lized to form carboxy terminal fragments (PTH-C), ami- no terminal fragments (PTH-N), and mid region PTH. During the past 50 years various assays for the determi- nation of PTH have been developed. The early genera- tion versions of PTH radioimmunoassays (RIA) were restricted to measure these N-terminal, mid-region, or C-terminal fragments, all of which circulate in high concentrations as they are cleared slowly [2]. Second generation versions of PTH assays use two monoclonal antibodies specific for the N- and C-terminal regions of the hormone [3] making rapid measurement of PTH fea- sible. Later radiolabels were replaced by chemilumines- cent substrates that improved the sensitivity of the as- says with higher reproducibility. The duration between sample collection and estimation is also important for correct PTH determination. Long term storage of whole blood at room temperature for in- tact PTH (iPTH) estimation is not feasible as its half- life in vivo is approximately 4 minutes [4]. Therefore, in diagnostic laboratories, stability is one of the major con- cerns in estimation of iPTH concentration. When sam- ple collection centers and diagnostics laboratories are located at different places and there are no proper re- frigeration or cooling facilities available, then the cor- rectness of PTH estimation is always in question. iPTH concentration is significantly stable in ethylenediamine- tetraacetic acid (EDTA) plasma when samples were stored at -80°C for long duration [5]. Short term storage (24 - 48 hours) at room temperature has also shown that iPTH concentration is almost stable in EDTA plasma and is preferred over serum as sampling method [6-10]. _____________________________________________ Short Communication accepted July 15, 2013