Stability of haematological parameters and its relevance on the athlete's biological passport model

The stability of haematological parameters is crucial to guarantee accurate and reliable data for implementing and interpreting the athlete's biological passport (ABP). In this model, the values of haemoglobin, reticulocytes and out-of-doping period (OFF)-score (Hb-60√Ret) are used to monitor the possible variations of those parameters, and also to compare the thresholds developed by the statistical model for the single athlete on the basis of its personal values and the variance of parameters in the modal group. Nevertheless, a critical review of the current scientific literature dealing with the stability of the haematological parameters included in the ABP programme, and which are used for evaluating the probability of anomalies in the athlete's profile, is currently lacking. In addition, we collected information from published studies, in order to supply a useful, practical and updated review to sports physicians and haematologists. There are some parameters that are highly stable, such as haemoglobin and erythrocytes (red blood cells [RBCs]), whereas others, (e.g. reticulocytes, mean RBC volume and haematocrit) appear less stable. Regardless of the methodology, the stability of haematological parameters is improved by sample refrigeration. The stability of all parameters is highly affected from high storage temperatures, whereas the stability of RBCs and haematocrit is affected by initial freezing followed by refrigeration. Transport and rotation of tubes do not substantially influence any haematological parameter except for reticulocytes. In all the studies we reviewed that used Sysmex instrumentation, which is recommended for ABP measurements, stability was shown for 72 hours at 4 ° C for haemoglobin, RBCs and mean curpuscular haemoglobin concentration (MCHC); up to 48 hours for reticulocytes; and up to 24 hours for haematocrit. In one study, Sysmex instrumentation shows stability extended up to 72 hours at 4 ° C for all the parameters. There are significant differences among methods and instruments: Siemens Advia shows lower stability than Sysmex as regards to reticulocytes. However, the limit of 36 hours from blood collection to analysis as recommended by ABP scientists is reasonable to guarantee analytical quality, when samples are transported at 4 ° C and are accompanied by a certified steadiness of this temperature. There are some parameters that are highly stable, such as haemoglobin and RBCs; whereas others, such as reticulocytes, mean cell volume and haematocrit are more unstable. The stability of haematological parameters might be improved independently from the analytical methodology, by refrigeration of the specimens.