Stability study of lactate dehydrogenase activity in serum samples at different temperatures and times according to Spanish Society of Laboratory Medicine recommendations

Introduction To ensure adequate quality of clinical samples, laboratories must control samples’ postanalytical preservation. We checked the stability limit of lactate dehydrogenase (LDH) and confirmed the 72-hour limit the manufacturer proposes, then evaluated sample stability under our working conditions using new recommendations for stability studies. Methods Leftover outpatient samples were randomly selected. Serum tubes with separator gel were used for primary sample collection. In a preliminary study of samples from 6 patients, we made determinations at baseline, 24, 48, and 72 hours for aliquots stored at room temperature and refrigerated. An extended study in refrigerated samples was performed on 10 samples of leftover serum at baseline and 12, 24, 36, 48, 60, and 72 hours. Results We found no substantial variation in samples at room temperature. In the extended study, an LDH decrease of 1.5% per day is expected up to 72 hours based on the formula PD% = 0.064 ×time [h]. Discussion The available literature on stability studies is extensive and varies in terms of working methodology. Therefore, laboratories should follow recommendations from standardized and updated documents. We modified manufacturer stability recommendations by reducing the stability of refrigerated LDH samples in our laboratory automation system from 72 hours to 48 hours.