The informational value and usefulness of serum retinoid measurements. Studies on biological variation, including infancy and pregnancy, and influence of fasting, antiepileptic drugs and ethanol

Sammanfattning: The aims of these studies were to evaluate retinoid measurements, more specifically the performance of all-trans and 13-cis retinoic acids methods in clinical experimental settings and to evaluate the informational value of these measurements in relation to S-Retinol. Biological and analytical variations for retinoids were evaluated for healthy subjects. The performance of the retinoic acid measurements generally satisfied clinical demands to identify deficiency and toxicity, and to monitor substitution treatment. However, due to the comparatively large biological variation, it is important to stratify populations in order to obtain separate reference intervals for sub-populations. Also, to identify minor deviations in the set-point of individual subjects, repeated sampling is recommended. For characterisation of vitamin A status, S-All-trans retinoic acid was found to give differential or additional information compared to S-Retinol (which is the most commonly used analysis in this context) in a number of situations. These were: - diurnal variations in S-All-trans retinoic acid but not in S-Retinol - alterations in retinoid metabolism in pregnancy (increasing S-All-trans retinoic acid while S-Retinol remains constant) - low retinoid concentrations in infants (placental cords) - lowered S-All-trans retinoic acid but not S-Retinol during antiepileptic medication. Although S-All-trans retinoic acid and S-Retinol both decreased during caloric restriction, it was evident that individual changes in S-Retinol were poor predictors of individual changes in S-All-trans retinoic acid. Our studies demonstrated that all-trans retinoic acid and 13-cis retinoic acid measurements gave additional information compared to retinol measurements. Determination of retinoic acids is useful and essential in studies on specific issues in vitamin A metabolism. S-All-trans retinoic acid is a promising analyte with considerable potential in a number of clinical situations, especially in vitamin A deficiency. More studies on the informational value of S-13-cis retinoic acid in relation to teratogenicity and toxicity are required.