C-reactive protein measured in dried blood spots from patients with cystic fibrosis.

There was no significant difference in C-reactive protein concentration determined in paired serum and eluates from dried blood spots collected on Guthrie cards; mean difference 0.6 microgram/ml (95% CI -3.3-2.2 micrograms/ml; n = 101). Dried blood spot samples were stable for up to 21 days and were unaffected by posting to the laboratory. In eight patients with cystic fibrosis undergoing specific antibiotic treatment for Pseudomonas aeruginosa pulmonary infection the fall in C-reactive protein concentration was not significantly different between serum and dried whole blood spot specimens. This method could be used to monitor infection and the response to antibiotic treatment.