Table 5.

Calculations used for number needed to screen to prevent one case of AZA‐induced leukopenia and the positive/negative predictive values with polymorphism of NUDT15 R139C (rs116855232)

NUDT15 R139C	Positive	Negative	Total	Notes
AZA‐induced leukopenia	7,030	570	7,600	Incidence = 7.60% Sensitivity = 92.5%
Control	19,866	72,534	92,400	Specificity = 78.5%
Total	26,896	73,104	100,000
	PPV = 26.14% (25.61–26.67%)	NPV = 99.22% (99.15–99.28%)		NNS to prevent one case = 15 (13–17)

A theoretical population of 100,000 has been assumed, and the number of individuals with the ADR calculated based on previous reported prevalence, and the number of population controls calculated by subtracting this figure from 100,000. The sensitivity and specificity of the genetic NUDT15 R139C (rs116855232) test for the c AZA‐induced leukopenia have been taken from Table 3 and the numbers in each of the four cells (a, b, c, and d) calculated. The PPV, NPV, and NNS were then calculated from the numbers in each cell (a, b, c, and d).

ADR, adverse drug reactions; AZA, azathioprine; NNS, number needed to screen; NPV, negative predictive value; PPV, positive predictive value.