Autor(s): D. Giavarina, G. Mezzena, B. Faresin, L. Bedin, E. Pozzo, G. Soffiati
Background. Preanalitical conditions strongly affect the measurement of the ammonia levels in plasma or serum, especially the time from drawing the blood sample to centrifugation. A refrigerate transport is recommended in association to the timeliness of the execution of the test. Aim of this study is to verify if the refrigeration preserves the blood integrity for the ammonia determination. Methods. we compared the results obtained from 3 blood samples of 19 healthy subjects, measured at time zero and after 120 min, stored a 4° and 25°C. Further, 3 blood samples from other 43 volunteers were evaluated after 3 hours of storage, at the same conditions. Results. the mean difference between t0 and t120 kept at 4°C was of 10.1 ± 6.3 mol/L (95%CI: 7.1 - 13.1); p < 0.0001. The difference between not refrigerated and refrigerated samples, after 120 min, was 0.4 ± 3.5 mol/L (95% CI: -1.3 - 2.1); p = n.s. The mean difference between t0 and t 180 kept at 4°C was of 26.3 ± 10.9 mol/L (95%CI: from 22.9 to 29.6); The difference between not refrigerated and refrigerated samples, after 180 min, was -1.4 ± 9.1 mol/L (95% CI: from -4.2 - 1.3); p = n.s. Conclusions. The ammonia levels increase in the blood samples related to the time from the drawing. There are no differences in the ammonia concentration afters 120 and 180 min between the samples stored at 4 and 25°C. Refrigeration do not prevent the integrity of the blood samples for this test and a timeliness transfer of the samples to the laboratory is mandatory for an accurate measurement of the ammonia.