[Technical Note Comparison of Whole Blood and Plasma Morphine

Abstract J Thirty paired samples of plasma and whole hemolyzed blood were obtained from patients undergoing surgery. Morphine concentrations were measured with the DPC serum morphine kit without prior treatment. In a regression analysis, the equation to the regression line was blood = 1.02 plasma + 1.0 ng/mL, and the correlation coefficient was 0.994. Radioimmunoassay screening of postmortem blood samples can be performed without prior sample treatment. Introduct ion Many immunoassay methods have been introduced over recent years for the detection of abused rugs in urine. Toxicolo-gists frequently are required to screen for drugs in other body fluids, however, and the most common of these is whole blood collected at postmortem examination and which is usually extensively hemolyzed. Measurement of low concentrations of drugs in whole hemo-lyzed blood poses many problems for immunological methods. The principal problem is a matrix effect, in which binding of drug, antibody, or tracer (radioactive or other) can occur to give spurious high or low values. Pretreatment of the sample by extraction obviates the speed and efficiency of immunological screening methods. This study describes the use of a coated-tube radioimmunoassay for morphine in plasma and whole hemolyzed blood in patients given morphine for peroperative analgesia. Methods Three patients undergoing body surface surgery and receiving 10 mg morphine sulphate pentahydrate intravenously for per-operative analgesia and anesthesia were studied. Each gave informed consent, and the study was approved by the local ethics committee