Blood sampling as a cause of anemia in a general ICU - a pilot study

The objective of our pilot study was to evaluate the influence of daily phlebotomy on patients' haemoglobin levels from our general intensive care unit.

We prospectively enrolled 35 patients who did not present with acute haemorrhage or developed it during the study period. For each patient we recorded: the diagnosis, age, sex, haemoglobin, hematocrit, SOFA and APACHE II score, blood volume drawn in standardized vials, number of blood tests ordered per day, fluid balance per day, number of ICU days. The collected data were analyzed using the linear regression model, paired t-test, receiver operating characteristic curves, and descriptive analysis. Statistical analysis was performed with SPSS v.17 trial version (IBM, NY, USA).

The mean volume of blood drawn per day was 18.1 (SD ± 14.4) ml and the number of blood tests was 3.8 (SD ± 1.75) per day. On univariate linear regression analysis both the blood volume drawn daily (p = 0.04) and the number of blood tests per day (p = 0.009) correlated with a drop in mean haemoglobin concentration. The difference in the mean value of haemoglobin at admission and discharge correlated with overall mortality (p = 0.03). The sensitivity of admission haemoglobin equal to 10.6 g/dL in predicting mortality was 82.4% with a specificity of 50%, (p = 0.019, AUC = 0.732).

We evidenced the predictive power of blood sampling and number of blood tests done on haemoglobin concentration. Besides the main objective of the study we noticed that the difference in the mean value of haemoglobin at admission and discharge correlated with overall mortality. Considering that blood sampling contributes to anemia among ICU patients, we should limit the daily tests undertaken, to the tests absolutely necessary for guiding our therapy.