DIAGNOSTIC EFFICACY OF SCREENING-TESTS FOR HEREDITARY HEMOCHROMATOSIS

Abstract

Hereditary hemochromatosis is transmitted as an autosomal recessive trait. Analyses of pedigrees suggest that the frequency of disease (proportion of homozygous individuals) in the general population is .apprx. 0.3% and that .apprx. 11% of the population are heterozygous. The genotype of 194 persons in 38 pedigrees was determined by HLA-A and HLA-B haplotyping. Likelihood analysis was then used to appraise the transferrin saturation test when used alone and in combination with the serum ferritin test to detect homozygosity and heterozygosity in these pedigrees. A single cut-off point of 55% for transferrin saturation and a cut-off point at the 90th percentile for the serum ferritin level were adequate for the detection of hemochromatosis if homozygosity was considered to be present when the results of one or both tests were positive. To further assess the value of the transferrin saturation test the percentages were stratified into 5 intervals. A percentage transferrin saturation of 75 or greater and a serum ferritin level above the 90th percentile ruled in homozygosity, whereas a percentage transferrin saturation of < 55 and a serum ferritin level at or below the 90th percentile ruled it out with confidence. The probability of heterozygosity rose to 90% when the percentage transferrin saturation was between 35 and 55 and the serum ferritin level was at or below the 90th percentile. The use of 5 cut-off points allowed the probability of homozygosity and heterozygosity in a pedigree to be estimated for all values of transferrin saturation. Although these screening tests are not recommended for use in the general population, they may be worth while in selected groups of patients.