How I investigate basophilia in daily practice

Abstract Basophilia is a rare disorder of the complete blood count (CBC) and its management in daily practice remains unclear. Two main factors explain this situation. On the one hand, the reliability of the basophil count is insufficient, whether it is performed by a microscopic slide examination or by a hematology analyser. On the other hand, our knowledge of conditions associated with basophilia is largely based on few case reports and on reviews that refer to older reviews. The association between basophilia and myeloid neoplasm, especially chronic myeloid neoplasm, is well established. Conversely, there are conflicting data on some benign medical conditions and it remains unclear where basophilia may be present. In this review, we have investigated the medical literature to define which medical conditions can lead to basophilia and which cannot, and we propose a practical approach to manage basophilia divided into 3 steps. First, we have to check the real existence of the basophilia by getting rid of spurious basophilia. Then, we have to look for symptoms that suggest reactive basophilia and for clue of a neoplastic cause. Finally, in case of suspicion of a myeloid neoplasm or persistence of the basophilia in the absence of a reactive cause, we have to decide which examinations need to be prescribed to confirm a neoplastic basophilia.