Blood draws

Frequent blood samples are a part of life during leukemia treatment. A complete blood
count (CBC) tells the physician how effective the drugs are and helps determine the
child’s susceptibility to infection. It is important to measure blood chemistries to
make sure that the liver and kidneys are not being damaged by treatment. (For a list
of normal blood counts, see Appendix B, Blood Counts and What They Mean.) During
induction and consolidation, transfusions are necessary when the red cell count or
platelet count gets too low.
Blood specimens are primarily used for three purposes: to obtain a CBC, to evaluate
blood chemistries, or to culture the blood to check for infection. A CBC measures the
types and numbers of cells in the blood. Blood chemistries measure substances con-
tained in the blood plasma to determine if the liver and kidneys are functioning
properly. Blood cultures help evaluate whether the child is developing a bacterial or
fungal infection. If only a CBC is needed, a finger poke will provide enough blood.
Blood chemistries or cultures require one or more vials of blood obtained from a vein
in the arm or the right atrial catheter.
Blood is usually drawn from the large vein on the inside of the elbow using a proce-
dure similar to starting an IV, except that the needle is removed rather than left in the
arm. The advice for starting an IV also applies to drawing blood from the arm.
Children with catheters usually have blood drawn from the catheter rather than the
arm or finger. These procedures are described in Chapter 8, Venous Catheters.