Purpose: High circulating levels of proinflammatory cytokines cause anemia, perhaps by interacting with erythropoietin production or biological activity. We characterize the relationships of systemic inflammation, erythropoietin, and hemoglobin.
Methods: Data are from the InCHIANTI (Invecchiare in Chianti, aging in the Chianti area) study population. A sample of 1270 persons aged 65 years or older and 30 men and 30 women from each age-decade 20 to 70 years were randomly selected from the residents in the Chianti, Italy, geographic area. Of the 1714 eligible persons, 1235 had complete data on inflammatory markers, erythropoietin, hemoglobin, potential causes of anemia, and other relevant covariates. Anemia was defined as hemoglobin less than 12 g/dL in women and less than 13 g/dL in men.
Results: Independent of age, sex, and hemoglobin, the number of elevated inflammatory markers (C-reactive protein, interleukin-6, interleukin-1beta, and tumor necrosis factor-alpha) was associated with progressively higher erythropoietin in non-anemic participants but lower erythropoietin in anemic participants. Findings were consistent across different causes of anemia. The threshold at which the effect of inflammation on erythropoietin reversed was close to 13.0 g/dL of hemoglobin.
Conclusions: Our findings suggest that anemia of inflammation evolves from a "pre-anemic" stage characterized by a compensatory increment of erythropoietin that maintains normal hemoglobin levels to a stage of clinically evident anemia in which erythropoietin levels are not high enough to maintain normal hemoglobin, possibly because of the inhibitory effect of inflammation on erythropoietin production. This hypothesis requires testing in a longitudinal study.