Pleural fluid: Are temperature and storage time critical preanalytical error factors in biochemical analyses?

Biochemical analysis of fluid is the primary laboratory approach in pleural effusion diagnosis. Standardization of the steps between collection and laboratorial analyses are fundamental to maintain the quality of the results. We evaluated the influence of temperature and storage time on sample stability. Pleural fluid from 30 patients was submitted to analyses of proteins, albumin, lactic dehydrogenase (LDH), cholesterol, triglycerides, and glucose. Aliquots were stored at 21°, 4°, and−20 °C, and concentrations were determined after 1, 2, 3, 4, 7, and 14 days. LDH isoenzymes were quantified in 7 random samples. Due to the instability of isoenzymes 4 and 5, a decrease in LDH was observed in the first 24 h in samples maintained at − 20 °C and after 2 days when maintained at 4 °C. Aside from glucose, all parameters were stable for up to at least day 4 when stored at room temperature or 4 °C. Temperature and storage time are potential preanalytical errors in pleural fluid analyses, mainly if we consider the instability of glucose and LDH. The ideal procedure is to execute all the tests immediately after collection. However, most of the tests can be done in refrigerated samples, excepting LDH analysis.