The relationship between elevated fibrinogen and markers of infection: a comparison of seasonal cycles

To test the hypothesis that higher levels of fibrinogen in winter are relat ed to infections via the acute phase response, we assessed seasonal variati on in fibrinogen and C-reactive protein, together with three other response s to infection: white cell count, human herpesvirus-6 IgC antibody and inte rleukin-6. Monthly blood samples from 24 subjects aged 75+ years were asses sed for fibrinogen, C-reactive protein, white cell count, and human herpesv irus-6 IgC antibody. Interleukin-6 was measured in seven. Seasonal variatio n of these measures was determined by the population-mean cosinor procedure . Fibrinogen had a significant seasonal variation with a winter peak (mid-F ebruary) 1.26 g/l above the corresponding summer trough. C-reactive protein had a late-February peak, 3.71 mg/l above the summer trough. No seasonal r hythm was found in any other response to infection investigated. This study provides no evidence that winter infections are responsible for the season al variation in fibrinogen or C-reactive protein. The explanation for the s easonal changes in these proteins remains unknown.