ORIGINAL ARTICLE P J M H S Vol. 7, NO. 3, JUL – SEP 2013 722 Comparison of Stability of PTH in Serum and in EDTA Plasma IMRAN ALI, ASMA SHAUKAT, LUBNA SARFRAZ, MUHAMMAD WASEEM ABSTRACT Aim: To determine the mean difference in concentration of PTH in EDTA plasma and serum at room temperature (22°C). Design: Randomized control trial. Setting: Department of Chemical Pathology, Quaid-e-Azam Medical College Bahawalpur. Methods: 560 volunteers were randomly divided into two groups A and B. To group A blood sample EDTA was added, whereas, blood samples from group B were analyzed without adding EDTA. About 10 ml of blood was drawn from each patient and serum was separated with in 30 min by centrifuge machine. The serum was then divided into three aliquots, to be analyzed as base line reading and at 24 and 72hrs. Results: Samples without preservative showed statistically significant decrease in PTH concentration from baseline after 24hrs (p value< 0.0001) and at 72hrs (p=0.0001). Whereas the EDTA samples were stable at 24 hrs (p=0.32) and 72 hrs (p=0.64). Conclusion: Use of EDTA plasma for PTH measurement greatly increases PTH stability even at room temperature. Keywords: Parathyroid hormone, stability, EDTA, preanalytical error. INTRODUCTION Measurement of intact parathyroid hormone (PTH) is essential to the diagnosis and management of metabolic bone disease, hypercalcaemia, hypocalcaemia and renal dystrophy. 1 The effect of specimen type, collection temperature, and storage temperature on the in vitro stability of PTH differ by method and platform 1 . Characterization of preanalytical effects unique to each method, platform, and patient population is important to prevent potential clinical misdiagnosis 1 . PTH is a peptide hormone hence it is susceptible to proteolytic degradation by enzymes which exist in tissues and extracellular fluid so if there is considerable time lapse between sample withdrawal and analysis, when no preservative is used to halt such proteolytic changes, then the concentration of such hormones can decrease significantly with time. Quality of a test performed in clinical laboratory does not merely depend on analytical aspects 1 but it also needs much care regarding sample handling, time lapse between drawing a sample and performance of required test, storage temperature and added preservatives 3 . Recent research studies show that most of the laboratory errors (32% to 75%), 4 are contributed by preanalytical phase 5 , so it is the need of time to ----------------------------------------------------------------------- Pathology Department, Quaid-i-Azam Medical College, Bahawalpur. Pakistan Correspondence to Dr. Imran Ali, Demonstrator Email: doctorimranali@yahoo.com improve this sector of laboratory procedures to yield better results 6 . In a study done at Armed Forces Institute of Pathology (AFIP) Rawalpindi the values of thyroid stimulating hormone (TSH) 7 and PTH 8 were found statistically different (p<0.05) after 24hrs (value PTH=11.3, TSH=0.99) and 72hrs (value PTH=7.3, TSH=0.33) respectively from 0hr (value PTH=12.7, TSH =1.3) with regard to duration and added preservatives. In a study conducted on PTH at Royal Perth Hospital, Western Australia, statistical analysis of all results indicated that serum values both at baseline and after three days were statistically lower than the target value (P 0.0001). Serum PTH value after three days of storage at room temperature was >60% lower than the baseline sample whereas EDTA sample PTH value was marginally higher (8%) 9 . Quaid-e-Azam Medical College Pathology laboratory, being a tertiary care laboratory, provides diagnostic facilities to the entire district and specimens from peripheral laboratories take 1-2 days to reach the QAMC laboratory. This time lapse shows a need to increase the stability of specimens, thus allowing for transportation of samples from remote areas to central laboratory. Stability of samples is a big issue in case of PTH especially if it reaches the laboratory after a significant time lapse. Outcome of this study helped in estimating the mean difference in concentration of PTH in samples with and without preservative and