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Distinction between homozygous and heterozygous subjects with hereditary haemochromatosis using iron status markers
1Department of Medicine Y, Gentofte Hospital, University of Copenhagen, Denmark.
The purpose of the present study was: 1) to evaluate which of the four iron status markers (serum iron, serum transferrin, serum transferrin saturation, serum ferritin) displayed the highest discriminatory potential in the distinction between homozygous patients with hereditary haemochromatosis and heterozygous relatives, 2) to suggest optimum cut-off values for these iron status markers, and 3) to demonstrate how these cut-off values change if the expected utility from a correct diagnosis is incorporated into the analysis. The patients and relatives were found by a nation-wide epidemiological survey. The study population consisted of 162 patients with clinically overt hereditary haemochromatosis and 84 asymptomatic heterozygous relatives. The statistical evaluation was performed using receiver operating characteristic (ROC) curve analysis. The diagnostic power of the iron markers is expressed as the area under the ROC curve. The optimum cut-off value is at the point where the slope of the ROC curve is equal to one. Changes in the optimum cut-off value at varying expected utility from a correct classification was estimated by changing the scaling of the ROC diagram. Serum iron and serum transferrin had the smallest area under the ROC curve, and were both unsuitable as discriminators. Near complete discrimination was obtained with serum transferrin saturation and serum ferritin concentrations, displaying the largest area under the ROC curve (0.991 and 0.998). The optimum threshold value for transferrin saturation was 61%, and for serum ferritin concentration 800 micrograms/l. The transferrin saturation level reflects the presence of the haemochromatosis allele, whereas the serum ferritin concentration indicates the degree of iron overload.(ABSTRACT TRUNCATED AT 250 WORDS)
The purpose of the present study was: 1) to evaluate which of the four iron status markers (serum iron, serum transferrin, serum transferrin saturation, serum ferritin) displayed the highest discriminatory potential in the distinction between homozygous patients with hereditary haemochromatosis and heterozygous relatives, 2) to suggest optimum cut-off values for these iron status markers, and 3) to demonstrate how these cut-off values change if the expected utility from a correct diagnosis is incorporated into the analysis. The patients and relatives were found by a nation-wide epidemiological survey. The study population consisted of 162 patients with clinically overt hereditary haemochromatosis and 84 asymptomatic heterozygous relatives. The statistical evaluation was performed using receiver operating characteristic (ROC) curve analysis. The diagnostic power of the iron markers is expressed as the area under the ROC curve. The optimum cut-off value is at the point where the slope of the ROC curve is equal to one. Changes in the optimum cut-off value at varying expected utility from a correct classification was estimated by changing the scaling of the ROC diagram. Serum iron and serum transferrin had the smallest area under the ROC curve, and were both unsuitable as discriminators. Near complete discrimination was obtained with serum transferrin saturation and serum ferritin concentrations, displaying the largest area under the ROC curve (0.991 and 0.998). The optimum threshold value for transferrin saturation was 61%, and for serum ferritin concentration 800 micrograms/l. The transferrin saturation level reflects the presence of the haemochromatosis allele, whereas the serum ferritin concentration indicates the degree of iron overload.(ABSTRACT TRUNCATED AT 250 WORDS)