Objectives: To study the distribution of serum ferritin concentration in adolescent boys and girls with and without a preceding mild infection.
Design: The prevalence of iron deficiency was studied in two representative samples. The first sample from 1990 comprised 207 boys and 220 girls. The second sample from 1994 included 620 boys and 624 girls. In total 1675 adolescents, 15-16 y old, 827 boys and 844 girls were studied.
Results: A significant shift of serum ferritin concentration towards higher values was observed in those who reported an upper respiratory infection with fever during the preceding month (P<0.001). Significant differences were found between serum ferritin values in healthy, not infected adolescents and serum ferritin values in those with ongoing infection, both in boys and girls in the two materials (P < 0.01), and in those with a mild infection during the preceding three weeks.
Conclusions: The prevalence of recent infection should be included as information when trying to assess the prevalence of iron deficiency on the basis of serum ferritin measurements and when examining relationships between iron status and composition of the diet. The findings imply that differences in prevalence of iron deficiency between different studies might partly be explained by differences in prevalence of simple respiratory infections. The diagnostic sensitivity of the serum ferritin assay for iron deficiency, using conventional reference limits, decreases for subjects with recent such infections; similarly, there will be a decrease in the diagnostic specificity for haemochromatosis.