An ELISA for plasma retinol-binding protein using monoclonal and polyclonal antibodies: plasma variation in normal and insulin resistant subjects.

OBJECTIVES Plasma retinol-binding protein (RBP) has been linked to insulin resistance and cardiovascular risk, yet little is know of its natural variation in plasma. We examined this in normal subjects and compared plasma levels and variability in lean subjects and subjects with the metabolic syndrome. METHODS We established an "in house" ELISA for plasma RBP and measured levels in 20 normal subjects over daylight hours and 2 subject groups, either lean or classified with the metabolic syndrome. RESULTS Plasma RBP in normal subjects did not vary over the day with no differences between males and females. There was also no difference in plasma RBP levels and between the age- and sex-matched lean subjects compared to the metabolic syndrome group. CONCLUSION The lack of variation in plasma RBP in normal subjects and the lack of difference between plasma RBP in normal and metabolic syndrome subjects suggest the link between plasma RBP and insulin resistance is tenuous. Investigating a large cohort over the diabetic non-diabetic spectrum may clarify this issue.