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The acute phase response is known to affect many biological parameters used to assess the iron and vitamin A status. Usually, C-reactive protein (CRP) values higher than 5 to 10 mg/L are taken as indicative of this response. Here we report changes occurring at much lower CRP values. A range of parameters (clinical chemistry, retinol, vitamin E, carotenoids, thyroid status, blood count, immunology) were measured in 101 healthy one-year-old children with no or only minimal symptoms of airway infection and CRP values below 6 mg/L on routine testing. Additionally, CRP values were measured by a high-sensitivity assay (detection limit 0.2 mg/L). When determined by a more sensitive assay, CRP values (median, 0.26 mg/L) revealed highly significant associations with parameters known to be influenced by the acute phase response. Using a limit of 0.6 mg/L (75th percentile), significantly lower levels were observed for transthyretin, iron, retinol, and beta-carotene in the group with the higher CRP levels. This relationship was confirmed intra-individually in a subgroup of 21 children who underwent a second blood draw about four weeks after the first one. The acute phase response is triggered at very low inflammatory levels with CRP values considerably lower than 5 to 10 mg/L, and can occur in apparently healthy children. A high-sensitivity CRP assay is necessary to detect this low level, and in the case of iron or vitamin A, it can help to avoid misclassification of the nutritional status.
Abraham et al. (Mon,) studied this question.