Pentraxin 3 stability in serum and urine samples at –20 °C during a 4-week period

Abstract Introduction The aim of our study was to examine the stability of pentraxin 3 (PTX3) in serum and urine samples during 4-week storage at –20 °C. Methods Ten routine leftover serum and urine samples were used in this study. The samples were stored at –20 °C over 4 weeks and analyzed each week in a single batch using the Human pentraxin 3 ELISA kit (BioVendor Group). Stability was expressed as a percentage difference between the initial measurement and the measurements taken weekly. Total error (33%) was used as the performance criterion for stability. Results The concentration of PTX3 decreases with time during storage at –20 °C in both serum and urine. The percentage difference exceeded the set criterion in serum samples at the third week of storage (percentage difference = –23.5% [95% CI, –36.6% to –10.5%]) and at the first week of storage in urine samples (percentage difference = –41.5% [95% CI, –63.1% to ‒19.8%]). Discussion Pentraxin 3 can be stored in serum samples for a maximum of 2 weeks at –20 °C before analysis to measure representative results. Because PTX3 is not stable in urine samples, such samples should be analyzed on the day of sample collection.