A stable liquid human reference serum

A procedure is described for the preparation of a liquid reference control suitable for use in calibration of both automated and manual chemical procedures. Pooled human serum was partially dehydrated under vacuum from the frozen state. Ethylene glycol was added to replace the water to produce a 30% solution. The stability of a liquid reference control so prepared was investigated by examining aliquots stored at room, refrigerator, and freezer temperatures for various storage times up to 568 days. Eighteen components were assayed with the Technicon Auto Analyzers SMA 6/60 and 12/60 in a tandem mode with creatinine and creatine phosphokinase channels replacing the glucose and urea nitrogen of the standard SMA 12/60. Initially specimens were examined daily, then at weekly, monthly, and longer intervals. Standard deviations and coefficients of variation were compared with those obtained on commercial lyophilized controls assayed during the same time interval. The results indicated that the ethylene glycol treatment can be used to produce a liquid reference control with stabilized enzyme activities and stable component levels.