Quality Assessment of the Genetic Test for Familial Hypercholesterolemia in The Netherlands

Table 3

Frequencies of mutation detection in the per-protocol study population.

Test result	Gold standard test^#		Total
	Mutation present	Mutation absent
Reference lab: mutation present	314	2	316
Reference lab: mutation absent	0	685	685
Total*	314	687	1001

∗Excluded the 2 individuals in whom switch of DNA samples was discovered before counter-expertise test had been performed (subjects A and B from Figure 1 and Table 2).
^#Gold standard test is defined as the overall conclusion after following the steps for mutation analysis in both the reference laboratory and the counter-expertise laboratory.
Overall accuracy = 999/1001 = 0.998, 95%. Confidence interval: 0.998−(1.96∗sqr(0.998∗(1.0--0.998))) to 0.998+(1.96∗sqr(0.998∗(1--0.998)))=0.911 to 1.00.
Sensitivity = 314/314 = 1.0, 95%. Confidence interval: 1.0−(1.96∗sqr(1.0∗(1.0--1.0))) to 1.0+(1.96∗sqr(1.0∗(1--1.0)))=1.00.
Specificity = 685/687 = 0.997, 95%. Confidence interval: 0.997−(1.96∗sqr(0.997∗(1--0.997))) to 0.997+(1.96∗sqr(0.997∗(1--0.997)))=0.891 to 1.00.
Likelihood ratio for a positive test = sensitivity/(1 − specificity) = 344, indicating that a positive result is 344 times more likely to occur in someone with the mutation according to the gold standard than in one without it.