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 similarly 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 the transfusion! 😁