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  • Title: Conjunctival impression cytology with transfer as a field-applicable indicator of vitamin A status for mass screening.
    Author: Carlier C, Coste J, Etchepare M, Amédée-Manesme O.
    Journal: Int J Epidemiol; 1992 Apr; 21(2):373-80. PubMed ID: 1428495.
    Abstract:
    The increasing importance of vitamin A deficiency in even its mild subclinical form underlines the need for a mass screening test. Clinical, biochemical and cytological methods of assessing vitamin A deficiency in a public health setting have been described and widely used. The cytological method shows promise because it enables early detection of vitamin A deficiency. However interpretation is problematic since histopathological changes are gradual with the progressive disappearance of goblet cells and appearance of enlarged epithelial cells. The reliability and validity of the impression cytology with transfer (ICT) test were assessed in order to produce a meaningful standard for this cytological method. The ICT test was performed in Senegal on 1451 children, in the course of two surveys conducted in 1989 and 1990 in rural areas. Reliability, estimated by Cohen's kappa test for evaluating intra-reader variability, and sensitivity were highest for the abnormal-normal classification (kappa = 0.91; 95% confidence interval (CI): 0.89-0.93; and sensitivity = 74%; 95% CI 66-82%). The ICT method is a cheap, noninvasive and easy test to perform in the field. This method is also reproducible and fairly sensitive according to the abnormal-normal classification. As illustrated by our proposed 50% cutoff of abnormal cytology calculated in relation to 5% of serum retinol values below 0.35 mumol/L criterion, ICT only requires a small sample for the assessment of the overall health of a community in contrast to xerophthalmia and blood vitamin A deficiency tests. In Senegal an ophthalmologist conducted eye examinations on 192 preschool children from 2 rural villages in Niakhar district in the Diourbel region in April 1989 and on 1259 preschool and school age children from 30 rural villages from Malicounda community in the Thies coastal region in February-March 1990 to assess the reliability and validity of the impression cytology with transfer (ICT) test as a field indicator of vitamin A status. Researchers also intended to standardize the cytological results. Cohen's kappa test revealed almost perfect agreement between the observed and expected interpretations of the conjuctival imprints for the classification abnormal-normal (kappa=0.91; 95% confidence interval [CI] for ICT=0.89-0.93). Thus the ICT test was reliable. Serum retinal concentrations indicated that the ICT test was specific for the deficient-nondeficient classification (serum retinal concentrations [SRC]=96%; 95% CI 93-97%) and fairly sensitive for the abnormal-normal classification (SRC=74%; 95% CI=66-82%). These serum retinal concentration results indicated that the ICT test was valid. The researchers proposed 2 classifications--normal and abnormal--to increase reproducibility of the ICT test. Since the ICT test can detect insufficient peripheral supply of vitamin A to the eye at an early stage and has only a 50% cut off, the ICT test can determine the public health of a community with only a small sample. Further the ICT test is a reproducible diagnostic test that is inexpensive, noninvasive, and easy to perform in the field.
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