Measurement of blood levels of 7-dehydrocholesterol in man by high-performance liquid chromatography.

A high-performance liquid chromatography procedure was established to measure 7-dehydrocholesterol (7DHC) in the blood. Interference studies were performed using 20 similar compounds likely to give analytical errors. 7DHC was extracted with a methanol chloroform mixture. Extraction recoveries were reproducible and acceptable, with low methodological variations from batch-to-batch. Results show that 7DHC is not detectable in the blood, contrary to the previous reports. Possible explanations for its absence in the blood are: (1) it is confined to the skin and is not present in the blood in this form; (2) because the molecule is labile, it is destroyed by the methods applied; (3) previous reports on 7DHC levels were based on non-specific methods.