Development of a rapid enzyme immunoassay for the detection of retinol-binding protein.

BACKGROUND

Retinol-binding protein (RBP) was chosen as a surrogate marker for retinol because of the close correspondence between retinol and RBP.

OBJECTIVE

To meet the need for rapid, cost-effective determination of vitamin A status in populations, a quantitative enzyme immunoassay (EIA) for detection of RBP was developed.

DESIGN

The resulting RBP EIA, a competitive assay, uses RBP adsorbed to microtest strip wells to compete with RBP in serum. The assay takes approximately 40 min.

RESULTS

With a reference panel of sera, test accuracy was found to be within 4% of expected values through the calibrated range of 0.48-1.92 micro mol RBP/L (10-40 micro g RBP/mL). Intraassay and interassay variability averaged 6.7% and 8.9%, respectively. Specificity testing showed no interference from other serum proteins, prealbumin, rheumatoid factor, bilirubin, estrogen, or C-reactive protein. The RBP EIA provided linear results between 0.43 and 1.80 micro mol RBP/L (9 and 38 micro g RBP/mL). Preliminary laboratory evaluations indicated that the RBP EIA correlates well with radial immunodiffusion for RBP and with HPLC for retinol, the current reference standard. A field evaluation in a population at risk for vitamin A deficiency (VAD) resulted in close correlation between RBP EIA measures and retinol measures by HPLC (R(2) = 0.82).

CONCLUSIONS

The RBP EIA is as reliable in estimating VAD as is HPLC retinol. After successful validations, the test should enable public health authorities to rapidly monitor VAD and track vitamin A status in populations.