Application of a rapid dark adaptation test in children

Biomarkers of Nutrition for Development (BOND)-Vitamin A Review

The Biomarkers of Nutrition for Development (BOND) project is designed to provide evidence-informed advice to anyone with an interest in the role of nutrition in health. The BOND program provides information with regard to selection, use, and interpretation of biomarkers of nutrient exposure, status, function, and effect, which will be especially useful for readers who want to assess nutrient status. To accomplish this objective, expert panels are recruited to evaluate the literature and to draft comprehensive reports on the current state of the art with regard to specific nutrient biology and available biomarkers for assessing nutritional status at the individual and population levels. Phase I of the BOND project includes the evaluation of biomarkers for 6 nutrients: iodine, folate, zinc, iron, vitamin A, and vitamin B-12. This review of vitamin A is the current article in this series. Although the vitamin was discovered >100 y ago, vitamin A status assessment is not trivial. Serum retinol concentrations are under homeostatic control due in part to vitamin A's use in the body for growth and cellular differentiation and because of its toxic properties at high concentrations. Furthermore, serum retinol concentrations are depressed during infection and inflammation because retinol-binding protein (RBP) is a negative acute-phase reactant, which makes status assessment challenging. Thus, this review describes the clinical and functional indicators related to eye health and biochemical biomarkers of vitamin A status (i.e., serum retinol, RBP, breast-milk retinol, dose-response tests, isotope dilution methodology, and serum retinyl esters). These biomarkers are then related to liver vitamin A concentrations, which are usually considered the gold standard for vitamin A status. With regard to biomarkers, future research questions and gaps in our current understanding as well as limitations of the methods are described.

Comparison of indices of vitamin A status in children with chronic liver disease

Malabsorption of fat-soluble vitamins is a major complication of chronic cholestatic liver disease. The most accurate way to assess vitamin A status in children who have cholestasis is unknown. The goal of this study was to assess the accuracy of noninvasive tests to detect vitamin A deficiency. Children with chronic cholestatic liver disease (n = 23) and noncholestatic liver disease (n = 10) were studied. Ten cholestatic patients were identified as vitamin A-deficient based on the relative dose response (RDR). Compared with the RDR, the sensitivity and specificity to detect vitamin A deficiency for each test was, respectively: serum retinol, 90% and 78%; retinol-binding protein (RBP), 40% and 91%; retinol/RBP molar ratio, 60% and 74%; conjunctival impression cytology, 44% and 48%; slit-lamp examination, 20% and 66%; tear film break-up time, 40% and 69%; and Schirmer's test, 20% and 78%. We developed a modified oral RDR via oral coadministration of d-alpha tocopheryl polyethylene glycol-1000 succinate and retinyl palmitate. This test had a sensitivity of 80% and a specificity of 100% to detect vitamin A deficiency. In conclusion, vitamin A deficiency is relatively common in children who have chronic cholestatic liver disease. Our data suggest that serum retinol level as an initial screen followed by confirmation with a modified oral RDR test is the most effective means of identifying vitamin A deficiency in these subjects.

The night vision threshold test is a better predictor of low serum vitamin A concentration than self-reported night blindness in pregnant urban Nepalese women

This study was conducted to validate the night vision threshold test (NVTT) as an indicator of night blindness. A total of 1401 pregnant women from the National Maternity Hospital participated in this study. Women were queried about night blindness and took the NVTT using standardized procedures after 10 min of dark adaptation. Sixteen percent failed the NVTT, but only 6.4% reported having night blindness. Blood samples from women who failed the NVTT (cases) and matched controls indicated the serum vitamin A (SVA) concentration was lower (P < 0.05) in cases (1.19 +/- 0.03 micromol/L) than in controls (1.29 +/- 0.03 micromol/L). The SVA concentrations did not differ between women who reported and did not report night blindness. The SVA concentration was correlated (r = 0.22, P < 0.001) with the NVTT scores. Twenty-five percent of women with an SVA < 0.35 micromol/L reported night blindness while 100% failed the NVTT. Nineteen percent of women with an SVA < 0.70 micromol/L reported night blindness while 73% failed the NVTT. A receiver operating characteristics analysis indicated that the NVTT had greater sensitivity (0.73 vs. 0.19) and less specificity (0.51 vs. 0.87) compared with reported night blindness for women with SVA < 0.70 micromol/L and greater sensitivity (100.0 vs. 0.73) and similar specificity (0.51 vs. 0.50) for women with SVA < 0.35 micromol/L. The NVTT identified women with low SVA and self-reported night blindness was misleading. We provide a preliminary algorithm to predict the population of women with low SVA concentrations.

Physiologic indicators of vitamin A status

Physiologic indicators reflect the functional consequences of vitamin A deficiency and may be particularly useful for detecting early perturbations in vitamin A status. In conjunctival impression cytology (CIC), epithelial morphology and the presence or absence of mucin spots and goblet cells allow samples, obtained by applying filter paper to the temporal conjunctiva, to be characterized as normal or typical of vitamin A-deficient keratinizing metaplasia. The validity of CIC has been established with reference to other indicators of vitamin A status, and a prevalence of > or =20% abnormal results has been suggested as indicative of a public health problem. However, interpretation of specimens requires considerable training, and nonresponsiveness to supplementation is a frequent problem, which limits the utility of CIC as a method for evaluating the impact of intervention programs. Several simplified field protocols for dark adaptation have been developed, including one in which dark adaptation is assessed by the responsiveness of the pupil to light. Night blind subjects have consistently shown abnormal results on this test, and a significant response to placebo-controlled dosing has been demonstrated for children and pregnant women. Scores have correlated significantly with serum retinol and relative dose response. Pupillary dark adaptation testing is acceptable to most children as young as 2 y old. Limitations of this technique include a time course for recovery after dosing as long as 4-6 wk, a testing time of 20 min, and the need for 1-3 d of training. Given its low cost, noninvasive nature, and lack of the need to transport samples, pupillary dark adaptation offers advantages over other techniques for assessing a population's vitamin A status.

A simple field test for identification of night-blindness

A simple and replicable field test to measure dark adaptation time has been developed. It required a darkened room with a 5 watt bulb covered with a piece of black cloth, a spherical white object of 22 cm diameter suspended vertically from a horizontal string, a stool, a black curtain, a Maxwell electronic photographic flash unit and a stop-watch. The spherical object behind the closed curtain was hung 1.5 m away from the subject either to his left or right, or in the centre of the room. The seated subject was then exposed to 3 consecutive flashes, the curtain drawn, and the time taken to identify the position of the object was noted on the stop-watch. The test was conducted for 3 consecutive days on non-night blind young adult girls (n = 46) of the high income group (PC); underprivileged school-age children (n = 44) with a positive history of night-blindness (NB), and their age/sex pair-matched (n = 44) non-night-blind controls (NNB). The NB group had a significantly higher mean dark adaptation time as compared to the NNB and PC groups (14.9 sec vs 11.9 and 11.3 sec respectively). The mean serum vitamin A levels of NB, NNB and PC groups (15.8, 17.5 and 29.5 micrograms/dl respectively) were correlated with the dark adaptation times.

Assessment of nutritional status: functional indicators of pediatric nutriture

The author speaks to the need to update our conceptual approach and our technical capacities for nutritional status assessment and to devise innovative ways to apply them to pediatric practice. The article discusses and evaluates conventional, static indices of nutriture and the importance of history and the physical examination. Focus is then placed on the concept of the functional assessment of nutritional status and its potential for clinical use.