Autoimmune hemolytic anemia in association with insect bites is a rare presentation, but delay in diagnosis can cause significant morbidity and mortality. Here, we report a case of Coombs positive hemolytic anemia after a wasp bite.

A 12-year-old male without significant past medical history was transferred to our hospital by his primary care physician with persistent fatigue, bilateral lower extremity pain, and history of undocumented fever. His laboratory work-up was remarkable for hemolytic anemia with hemoglobin of 4.5 g/dL, reticulocyte count of 6.4%, elevated indirect bilirubin of 9.2 mg/dL, and lactate dehydrogenase (LDH) of 1702 U/L. His serum creatinine kinase was also elevated at 1927 U/L.

Upon arrival to our hospital, he was febrile (102.9oF) and had tachycardia. On physical exam, he was icteric and noted to have 1×2 cm and 1×3 cm eschars with surrounding induration on left side of his abdomen. Direct anti-globulin test (DAT) was positive with anti-IgG reagent (3+). He was admitted to the pediatric intensive care unit (PICU) with a cinical diagnosis of auto-immune hemolytic anemia (AIHA) due to insect bite. Mother gave a history of seeing wasps in the house on the day of bite and per the toxicologists, the rash was consistent with a hymenoptera bite.

Upon admission, he was given blood transfusion and started on methylprednisolone. He was also started on empiric vancomycin and cephalosporin, which were discontinued 48 hours later after negative blood cultures. During his course in the ICU, he continued to require blood transfusion with ongoing drop in hemoglobin. After three days of steroids, hemolysis stopped and his hemoglobin stabilized at 8.9 g/dL. Creatinine kinase, LDH, and reticulocyte count also decreased. He was discharged home after two days on a steroid taper with recommendations for outpatient follow up. Infection was ruled out on the basis of negative cultures. No other known exposure to a new medicine was elicited. The rash being localized, specific history to a topical agent was asked but was negative. Moreover, DAT positive for IgG reagent in the presence of history of exposure to wasp in the house was suggestive of warm auto-immune hemolytic anemia (AIHA).

AIHA is defined as the destruction of circulating red blood cells (RBCs) in the setting of anti-RBC autoantibodies that optimally react at 37°C [1]. About 50% of the warm AIHA cases are called primary because no specific etiology can be found, whereas the rest are recognized as secondary to lympho-proliferative syndromes, malignant diseases, rheumatologic diseases, especially systemic lupus erythematosus, infections (mostly viral), drugs, or a previous transfusion or trans-plantation. Laboratory work-up of the patient was not suggestive of any of these secondary causes.

This presentation caused by insect bite is a rare clinical entity. The exact mechanism of this type of hemolytic anemia is unclear. However, it has been proposed that the toxin from the insect bite alters the red blood cell membrane structure making it more vulnerable to complement-mediated lysis [1]. Medical management primarily consists of supportive treatment. General consensus for first line pharmacologic treatment is glucocorticoids. It is believed that steroids not only decrease antibody production, but also suppress the effect of tissue macrophage phagocytosis and direct effect on auto-antibody red blood cell affinity [2,3].

Such presentations of AIHA due to insect bites can pose a diagnostic challenge and can potentially be fatal. This case demonstrates the importance of a high level of suspicion to allow for timely recognition and intervention [2,4].

1. Tambourgi DV, 　Morgan BP,　 de Andrade RM, et al. Loxosceles intermedia spider envenomation induces activation of an endogenous metalloproteinase, resulting in cleavage of glycophorins from the erythrocyte surface and facilitating complement-mediated lysis. Blood. 2000; 95:683-91.

2. Naik R. Warm autoimmune hemolytic anemia. Hemato-Oncol Clin North Amer. 2015;29:445-53.

3. Monzon C, Miles J. Hemolytic anemia following wasp sting. J Pediatr. 1980;96:1039-40.

4. Biswas S, Chandrashekhar P, Varghese M. Positive hemolytic anemia due to insect bite. Oman Med J. 2007;22:62-3.