Modelling sensitivity, specificity and predictive values of hematuria testing using reagent sticks in the diagnosis of Schistosoma haematobium infection
Etard, J.E.
Bulletin de la Societe de Pathologie Exotique 97(1): 24-28
2004
ISSN/ISBN: 0037-9085 PMID: 15104153 Document Number: 572036
This study assessed the influence of age, gender and intensity of infection taken together on the performance of the diagnostic test by fitting logistic regression models. During a socioeconomic study of schistosomiasis carried out between 1989 and 1991 in a rice-growing area in Mali, West Africa, haematuria was detected by reagent strips among 2873 six-year-old and more subjects randomly chosen from 14 villages. The gold standard of infection was provided by parasite egg counts. Observed sensitivities, specificities, and predictive values were calculated by the standard two-by-two tables. The influence of age, gender, and intensity of infection on these parameters were studied by two logistic models. The first one modelled sensitivity and specificity and the 2nd one modelled predictive values. Large variations in the observed values of sensitivities, specificities and predictive values by age and gender were observed. The best fitted model for sensitivity and specificity included infection status, age, gender, intensity and an age by gender interaction. For the predictive values, the best model included haematuria, age, and an haematuria by age interaction. Given the large variations in the performances across the covariates strata defined by cross-tabulation of the age/gender and intensity categories, this modelling approach provided a more realistic appraisal of the performances than using overall values obtained from a general two-by-two table. It allowed to assess the effect of the covariates of interest on the performances of the test and provided an adjustment of the performances on these covariates. The best fitted model was able to provide estimates of sensitivity for each age/gender stratum as a function of the intensity of infection, which could not be done by using the two-by-two table approach. A decrease in sensitivity adjusted for intensity of infection above 10 years of age among males is discussed. This modelling approach also uses all the information available and not only the data from the stratum of interest.