Retinol binding protein as a surrogate measure for serum retinol: studies in vitamin A-deficient children from the Republic of the Marshall Islands.
BACKGROUND
Serum retinol is transported by retinol binding protein (RBP), which has one high-affinity binding site for retinol; consequently, the molar ratio of retinol to RBP in the circulation is approximately 1 to 1. In vitamin A deficiency (VAD), both serum retinol and RBP decline. However, the retinol-RBP relation has not been well studied in populations with a high incidence of severe VAD.


OBJECTIVE
The purpose of this study was to determine whether RBP is a good surrogate for serum retinol at the very low retinol concentrations encountered in VAD.


METHODS
The stoichiometric relation between retinol and RBP was studied in 239 Marshallese children: 65 with severe VAD (< or = 0.35 micromol retinol/L), 94 with moderate VAD (0.36-0.70 micromol retinol/L), and 80 with vitamin A sufficiency (> 0.70 micromol retinol/L).


RESULTS
Excellent correlation between retinol and RBP (r = 0.94) was observed across all retinol concentrations. Severe VAD was predicted with 96% sensitivity and 91% specificity on the basis of an RBP cutoff of < or = 0.48 micromol/L, whereas moderate VAD was predicted with 87% sensitivity and 98% specificity on the basis of an RBP cutoff of < or = 0.70 micromol/L.


CONCLUSIONS
The use of RBP results in the classification of essentially the same children with VAD as does retinol, and RBP is an excellent surrogate for serum retinol. Considering the relative ease of measuring RBP with immunodiagnostic kits compared with that of serum retinol by HPLC, the use of RBP concentrations to assess VAD may be particularly advantageous in field settings. Consequently, measuring RBP concentrations may be a practical alternative to measuring serum retinol in population surveys assessing the prevalence of VAD.
Gamble
M V
MV
Institute of Human Nutrition and the Departments of Medicine and of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, USA. mgamble3@ix.netcom.com
Ramakrishnan
R
R
Palafox
N A
NA
Briand
K
K
Berglund
L
L
Blaner
W S
WS
D000209:Acute-Phase Proteins / Q000032:analysis; D015362:Child Nutrition Disorders / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D002664:Child Nutritional Physiological Phenomena; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008849:Micronesia / Q000453:epidemiology; D015596:Nutrition Assessment; D011863:Radioimmunoassay; D012177:Retinol-Binding Proteins / Q000032:analysis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D014801:Vitamin A / Q000097:blood*; D014802:Vitamin A Deficiency / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology
D000209:Acute-Phase Proteins; D012177:Retinol-Binding Proteins; D014801:Vitamin A