THE INFLUENCE OF PREANALYTICAL FACTORS ON CONCENTRATIONS OF MORPHINE AND METABOLITES IN PATIENTS RECEIVING MORPHINE

To examine the importance of preanalytical factors on the sample conce ntration of morphine, morphine-3-glucuronide and morphine-6-glucuronid e, blood samples were drawn in sets of four from 21 patients who were given morphine due to chronic pain or as premedication prior to surger y. Three different sampling tubes, different combinations of incubatio n temperature and time, and different temperatures during centrifugati on were used and compared to reference standard treatment of blood sam ples using analysis of variance. Blood samples taken in EDTA tubes pro duced significantly higher (4.8%) concentrations of morphine compared with the reference levels obtained in heparin glass tubes. Incubation of blood samples al body temperature resulted in significantly higher (4.4%) morphine levels compared to reference levels. None of the other conditions studied influenced the sample concentrations of morphine s ignificantly. The levels of the metabolites were not significantly aff ected under any of the tested conditions. Even if the preanalytical fa ctors investigated in this study had little influence on the results, a standardised procedure is recommended for handling of blood samples for analysis of morphine and its metabolites.