Dried blood spot test estimation of urea.

The analysis of urea in serum and whole blood samples dried onto filter paper has been investigated. In both cases the sample volume is not critical nor is the volume of sample applied to the filter paper if sample discs of consistent dimensions can be punched from the dried paper. The method must be calibrated by a serum-based material not an aqueous standard, presumably because of a matrix effect. A coefficient of variation of approximately 6% has been achieved over a wide range of urea concentration and the method has been shown to correlate well with a standard laboratory procedure. The technique has a particular application to neonatal capillary samples.