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Use of serum retinol-binding protein for prediction of vitamin A deficiency: effects of HIV-1 infection, protein malnutrition, and the acute phase response^1,2,3

¹ From the Departments of Epidemiology (JMB, JKK, and LL), Biostatistics (BAR), Laboratory Medicine (DDB and MHW), and Medicine (MHW, JKK, and RSM), University of Washington, Seattle; Coast Provincial General Hospital, Mombasa, Kenya (KM); and the Department of Medical Microbiology, University of Nairobi, Nairobi, Kenya (JJB).

Background: Serum retinol is the most commonly used indicator of vitamin A status. Retinol is transported in a 1-to-1 complex with retinol-binding protein (RBP). RBP is easy and inexpensive to measure, and studies have shown a high correlation between concentrations of RBP and concentrations of retinol. The performance of RBP in the context of infection or protein malnutrition, however, has not been evaluated.

Objective: Our aim was to determine whether RBP is a good surrogate measure for retinol in the context of HIV-1 infection, protein malnutrition, and the acute phase response.

Design: The relation between RBP and retinol was examined in a cross-sectional study of 600 Kenyan women.

Results: There was a high correlation between concentrations of RBP and those of retinol (r = 0.88). When equimolar cutoffs were used, RBP predicted marginal vitamin A status (retinol < 1.05 µmol/L) with 93% sensitivity and 75% specificity and vitamin A deficiency (retinol < 0.70 µmol/L) with 91% sensitivity and 94% specificity. Similarly high sensitivities and specificities were found among subgroups with HIV-1 infection, a positive acute phase response, and protein malnutrition. Protein malnutrition and a positive acute phase response were common, especially among HIV-1–infected women, and were independently and synergistically associated with lower RBP concentrations.

Conclusions: Equimolar RBP cutoffs predict vitamin A deficiency with high sensitivity and specificity, even in the context of infection and protein malnutrition. Like retinol, RBP may not accurately identify true vitamin A status under all conditions, because the acute phase response and protein malnutrition depress RBP concentrations. However, RBP may be a simple, inexpensive tool for assessment of vitamin A deficiency in population studies.

Key Words: Vitamin A • retinol • micronutrient deficiency • retinol-binding protein • nutritional assessment • nutritional status

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