Patients with sickle cell anemia (SCA) frequently (~55%) demonstrate absolute eosinophil count (AEC) (>450 cells/uL) during non-crisis steady state without significant change during sickle cell crisis [1-4]. Although the exact mechanism for this finding is not clear, it may be related to elevated plasma levels of circulating factors such as eotaxin, IL-5, and GM-CSF in SCA [2,3].

Cumulative data from 3 independent cross-sectional studies involving 131 SCA patients reported a mean AEC of ~498 cells/u (range 490-504 cells/uL) when not in crisis [2,3,6]. Surprisingly, two additional studies evaluating 200 patients did not observe a significant difference in AEC between steady- and crisis-states [1,4].

The significance of elevated AEC in patients with SCA is unclear. Of interest, several studies of eosinophils isolated from patients with SCA have demonstrated increased eosinophil adhesion to blood vessels, degranulation, and reactive oxygen species production compared to healthy controls [5,6]. In another study, hydroxyurea was shown to reduce eosinophil adhesion and degranulation [2].

While it is unknown whether eosinophils directly contribute to the development of vaso-occlusive crisis, these studies suggest eosinophils may be an important therapeutic target in SCA. 

Bonus pearl: Did you know that low eosinophil count may help predict infection in SCA patients? A retrospective study of SCA patients with and without infection showed that relative eosinopenia (0.025 compared to 0.2 x 10⁹ cells/L) was highly sensitive (100%) and specific (93.3%) for infection [7].

Contributed by Michael Nance MD, PhD, Department of Medicine, Mercy Hospital-St. Louis, St. Louis, Missouri

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References:

1. Ekeke GI. Sickle cell disease: some haematological changes in steady state and crisis. Biomed Biochem Acta 1987; 46:S197-S201. https://pubmed.ncbi.nlm.nih.gov/3593298/
2. Pallis FR, Nicola Conran, Kleber Yotsumoto Fertrin, Sara T. Olalla-Saad, Fernando Ferreira Costa, Carla Fernanda Franco-Penteado; Altered Functional Properties of Eosinophils In Sickle Cell Anemia and Effects of Hydroxyurea Therapy. Blood 2010; 116 (21): 2656. https://doi.org/10.1182/blood.V116.21.2656.2656
3. Conran N, Saad ST, Costa FF, Ikuta T. Leukocyte numbers correlate with plasma levels of granulocyte-macrophage colony-stimulating factor in sickle cell disease. Ann Hematol. 2007; 86(4):255-261. https://pubmed.ncbi.nlm.nih.gov/17205286/
4. Klouda T, Raybagkar D, Bernstein B, Apollonsky N, “Changes in Blood Profile from Steady State in Patients with Sickle Cell Anemia Admitted for Vaso-occlusive Crisis and Acute Chest Syndrome”, Advances in Hematology, vol. 2020, Article ID 3656717, 5 pages, 2020. https://doi.org/10.1155/2020/3656717
5. Canalli AA, Conran N, Fattori A, Saad ST, Costa FF. Increased adhesive properties of eosinophils in sickle cell disease. Exp Hematol. 2004; 32(8):728-734. https://pubmed.ncbi.nlm.nih.gov/15308324/
6. Pallis FR, Conran N, Fertrin KY, Olalla Saad ST, Costa FF, Franco-Penteado CF. Hydroxycarbamide reduces eosinophil adhesion and degranulation in sickle cell anaemia patients. Br J Haematol. 2014; 164(2):286-295. https://pubmed.ncbi.nlm.nih.gov/24383847/
7. Ahmed, SG and Uraka, A. Eosinopenia as a marker of infection in patients with sickle cell anemia: A preliminary report. Int. J. Biomed. Health Sci. 2010. 6(1):57-61. http://www.ojs.klobexjournals.com/index.php/ijbhs/article/viewFile/671/741

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!