Are anemia labs still reliable post-transfusion?

As a hospitalist at a bigger referral hospital with transfers coming in every day, this is a common scenario : I get a call about a patient who was found to be severely anemic on evaluation locally, cause is not clear yet. But before I can request checking some basic anemia labs like Iron / TIBC / Ferritin / Retic Count etc, they tell you blood was already transfused ! Occasionally some blood sample from previous draw might still be left for running labs but if not – is the diagnostic window of opportunity lost ? It is a common belief in the medical community that blood transfusion can skews anemia work-up labs.

I dug out some studies on this issue. Surprisingly all hope is not lost post-transfusion! A 2018 paper on a study on 77 patients comparing labs pre and post-transfusion (within 48-72 hours) found no significant changes in common anemia work-up labs – including B12/RBC-Folate/Iron/Ferritin/TIBC/Hemolytic markers. Even if these labs changed post-transfusion, they were still diagnostically useful for anemia in 97-98% cases. This was just done after a single unit of blood however. A 2006 study tried in 19 adults similar using 2 units of PRBC and checked various labs at 6, 12, 24 and 48 hours post-transfusion, Results showed unchanged pre & post-transfusion levels of Ferritin, Transferrin, B12, LDH & Haptoglobin levels. Serum Iron initially up but back to baseline after 24 hours. Only persistently changed lab was RBC-Folate, thus concluding that any anemia including hemolytic anemia could be diagnosed after blood transfusion, especially after 24 hours, except for folate deficiency. A much older 1993 study however concluded that at least iron and transferrin saturation are best done pre-transfusion , initial rise noted in 24 hours then no rise after. A separate study on transfusion effects on thalassemia patients in 2013 found no changes in pre and post-transfusion Ferritin and Reticulocyte count.

💡 Most anemia work-up labs are ok to do even if your patient already got blood transfusions – at least up to 2 units (beyond 2 units we don’t know for sure)- except for RBC / Serum folate levels. It may still be better to give it 24 hours post-transfusion to run diagnostic tests for anemia for more accurate results. If possible do these tests before the third unit of blood is given ! So don’t pull your hair if anemia labs weren’t done before transfusion! 😁