Stability of Parathyroid Hormone in Serum versus Plasma in Patients with Chronic Kidney Disease

Abstract

Objective: To determine the stability of parathyroid hormone in patients with chronic kidney disease both in serum and ethylenediaminetetraacetic acid (EDTA) plasma tested at room temperature. Methods: This is a prospective study conducted at Princess Iman Centre for Research and Laboratory Sciences, King Hussein Medical Center Jordan. A total of 94 patients were included with age range between 10 years and 65 years, of which 42.5 % male and 57.5% were female. From each patient 5 ml EDTA acid and 10 ml gel separator (with clot activator) tubes were collected and analyzed in a time period between 1/7/2015 and 1/11/2015. The plasma and sera were analyzed for intact parathyroid hormone within 6 hours of collection (baseline) and after 48 hours stored at room temperature, using immulite 2000 intact parathyroid hormone assay. Mean parathyroid hormone value, median, and differences for sera and EDTA samples at baseline and after 48 hours of collection were calculated and evaluated using Microsoft excel sheet. Results: Serum samples analysed after 48 hours from the collection time showed significant difference in their mean concentration value from the baseline mean value. Regarding EDTA acid plasma samples, their analysis after 48 hours showed a little decrease in parathyroid hormone concentration from the baseline value, which was not significantly different. The percentage of difference between baseline mean value and 48 hours mean value was 7.91 % for EDTA acid plasma samples and 11.1% for serum samples. Conclusion: The study showed that the parathyroid hormone was more stable in EDTA acid plasma sample than serum at baseline and after 48 hours of collection at room temperature. Serum samples gave inaccurate and false low results. Therefore, plasma measurement for parathyroid hormone analysis is preferred and advised. However, reference range for PTH concentration in plasma should be established if it is needed to be adopted for routine clinical use.