TABLE 7.

Overview of currently available biomarkers for the assessment of vitamin A nutrition¹

	Usefulness assessment²
	Exposure			Status			Function			Effect
Biomarker name	Research	Clinical	Program	Research	Clinical	Program	Research	Clinical	Program	Research	Clinical	Program
Dietary assessment	++	0	+	0	0	0	0	0	0	0	0	+
Functional tests	+	+	+	+	+	+	++	++	+	+	+	+
Dark adaptation
Electroretinography
Pupillary threshold
Biochemical tests
Serum retinol	+	+	+	++	++	+	++	++	0	+	0	+
RBP	+	+	+	++	++	+	++	++	0	+	0	+
Dried blood spots	++	++	0	+++	++	++	++	+	0	0	0	+
Breast-milk retinol	+	+	+	+	+	+	0	0	0	+	0	+
RDR	0	0	0	+	0	0	+	+	0	+	0	+
MRDR	0	0	0	++	+	++	++	++	++	++	++	++
Isotope dilution	++	0	0	++	0	+	0	0	0	++	0	+
Serum retinyl esters	+	+	+	+	+	+	0	0	0	0	0	0
Liver samples	+	+	0	+	+	0	0	0	0	0	0	0
Radio-isotopes	+	0	0	+	0	0	+	0	0	+	0	0
Proteomics or nutri-genomics³	?	?	?	?	?	?	?	?	?	?	?	?

Usefulness assessment uses the following grading system: 0, Not useful for the specific purpose; +, Useful to some extent and in certain population groups, but either not commonly used or has important disadvantages (e.g., no reference values); ++, Useful in certain population groups, often used with some limitations (e.g., lack of specificity or sensitivity); +++, Useful, often used in relevant population groups, with no or only minor limitations; ?, Unknown utility for vitamin A status assessment at this time. MRDR, modified relative dose response; RBP, retinol-binding protein; RDR, relative dose response.

Exposure means that the biomarker responds to dietary vitamin A intake, status means that the biomarker measures vitamin A status, function means that the biomarker measures a shift in function, and effect means that the biomarker is affected by deficiency of vitamin A. Research means that the biomarker can be used in research settings for evaluation and intervention outcomes, clinical means that the biomarker can be used in clinical settings at the individual level, and program means that the biomarker is applicable to program evaluations that usually include population assessments with large numbers of individuals.

Not discussed systematically in this article.

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TABLE 7.