Effects of blood sample volume on hematocrit in critically ill children and neonates

There are no studies correlating the volume of blood taken from children and hematocrit (Hct) stability, relating those changes to duration of stay, severity of illness or weight. Earlier studies in neonates suggest that repeated sampling results in a drop in Hct.

To characterize the changes in Hct in children of all ages admitted to intensive care over a 5-day period following routine blood volume sampling.

We undertook an open prospective observational study. Eligible children were recruited sequentially and data recorded for 5 days following admission. The bedside nurse recorded the daily volume of blood samples taken and transfusions given. Daily Hct was noted from the routine full blood count. The relationship between changes in Hct and blood sample volume and transfusion requirement was studied.

There were no differences in mean Hct on admission at end of the study (P = 0.69, n = 30) nor in the median blood volume sampled between transfused and nontransfused groups (7.5 ml.kg(-1) vs 7.9 ml.kg(-1), P = 0.88). The largest blood sample volumes were taken on admission and from the smallest patients.

We have quantitated the change in Hct and size of blood volume taken for routine laboratory studies. We suggest that children can tolerate 0.25 ml.kg(-1).day(-1) blood sampling without a fall in Hct and sampling can be tailored to the individual child according to the admission Hct.