With a simple calculation, the fraction of platelets remaining can be used to estimate the residual hemoglobin S percentage in sickle cell disease patients undergoing automated red blood cell exchange.

OBJECTIVES: Automated red blood cell exchange (RBX) is an important treatment for patients with sickle cell disease (SCD). Although not specifically targeted for removal, platelets (PLTs) are collected along with red blood cells during RBX. We sought to determine whether the pre- and post- RBX PLT counts could be used to derive the post-procedure hemoglobin S% (HgbS%).

METHODS: Using the pre- and post- RBX lab values of 59 SCD patients undergoing 112 RBX procedures over 1 year, we derived mathematical formulas which estimate the post-RBX HgbS% based on the pre-RBX HgbS%, the pre- and post- RBX PLT, and a correction factor.

RESULTS: For patients with pre-RBX HgbS > 40%, the mathematically derived post-RBX HgbS% was statistically indistinguishable from the measured post-RBX HgbS%.

CONCLUSIONS: Using a simple formula, pre- and post-RBX platelet counts can provide a rapid approximation of the measured post-RBX HgbS% in patients with SCD.