Loss of human chorionic gonadotropin in urine during storage at − 20 °C

► We studied factors affecting stability of hCG in urine at various temperatures. ► hCG was lost in many urine samples during storage at − 20 °C. ► Added urea caused a rapid hCG loss, which glycerol prevented. ► Urine should not be stored at − 20 °C before analysis of hCG. ► hCG is stable for months at − 80 °C and for weeks at + 4 °C.