Association of the blood eosinophil count with end-organ symptoms

Eosinophilia may cause organ dysfunction, but an exact relation between eosinophil blood counts and adverse outcomes has not been described. The aim of the study is to associate in one model both normal and increased blood eosinophil counts to the subsequent development of common conditions in internal medicine, in which eosinophil granulocytes may play a role for the symptoms.

From the Copenhagen Primary Care Differential Count (CopDiff) Database, we identified 359,950 individuals with at least one differential cell count (DIFF) during 2000-2007. From these, one DIFF was randomly chosen. From the Danish National Patient Register we ascertained organ damage, within four years following the DIFF. Using multivariable logistic regression, odds ratios were calculated and adjusted for previous eosinophilia, sex, age, year, month, CRP and comorbid conditions.

Risks for skin- and respiratory disease were increased from above the median eosinophil count of 0.16 × 10⁹/l and reached a plateau around 1.0 × 10⁹/l. Furthermore, risks of most outcomes also increased when the eosinophil count approached zero.

The observed U-shaped association with a plateau of risks around 1 × 10⁹/l indicates that the risk for symptoms due to eosinophilia do not increase proportionate at higher counts. This study demonstrates for the first time that there is indeed an increased risk below median count of 0.16 × 10⁹/l for an increased risk for the same manifestations. Clinically, it means that a normal or even low count of eosinophils do not rule out a risk for organ affection by eosinophils, and may contribute to explain, why patients may have normal eosinophil counts in e.g. asthma or allergy and still have symptoms from the lungs and skin, most likely explained by the extravasation of eosinophils.