[Blood volume for biochemistry determinations--laboratory needs and everyday practice]

Blood loss due to diagnostic phlebotomy jest a very serious problem, especially for newborn, infants and critically ill patients on intensive care units. Although single blood loss can be easily tolerated in adults, in small babies and in patients who are frequently monitored based on laboratory tests iatrogenic anaemia can occur.

To evaluate the blood volume drawn for routine biochemistry tests in relation to patient age and the number of parameters requested.

Blood volume drawn for routine biochemistry measurements from patients hospitalized in University Children's Hospital (N = 2980, children age from one day to 18 years) and in University Hospital (N = 859, adults, aged > 1.8 years) in Cracow has been analyzed. Blood volume was calculated based on regular tube diameter and blood heights in the tube. In case of microvettes the blood volume was 0.2 ml. Statistical analysis has been performed by using PRISM 5.0. The statistical significance was set at p < 0.05.

The mean values of blood volume were 3.02 +/- 0.92 ml and 4.12 +/- 0.68 ml in children and adults, respectively. Analyzing blood volume drawn in children using both microvettes and regular tubes, significant correlation between blood volume and patient age (p < 0.001) as well the number of requested parameters (p < 0.001). The latest relationship was true only for up to five parameters. However, analyzing the blood volume drawn into only into regular tubes blood volume was not related to patients age and number of laboratory tests requested. The proportion of microvettes used for blood collection was highest for newborns and infants, and in all cases where only one to three laboratory tests were requested.

1. All educational programs for nurses and doctors should include the information about current laboratory automation and methods miniaturization; 2) The amount of blood volume needed by laboratory for the requested number of tests should always be taken into account when diagnostic phlebotomy is necessary.