Table 4—

Cut-off values (determined with the optimal criterion method#) and performances of serological scores with electrosyneresis

VariablePrevalence %Positive serologySeSpPPVNPV
Discrete20>-0.3549957188
25>-0.4455937286
35>-0.5361897581
Dichotomous20ND
25>-0.7660855786
35>-0.7866806481
  • Se: sensitivity (probability of a positive test outcome in a hypersensitivity pneumonitis (HP) individual); Sp: specificity (probability of a negative test outcome in a non-HP individual); PPV: positive predictive value (probability of having HP when serological score is above the cut-off value); NPV: negative predictive value (probability of having HP when serological score is equal to or below the cut-off value); ND: nondiscriminative. #: S = ((1–P)/P)((CFP–CTN)/(CFN–CTP)), where S is the slope of the receiver-operating characteristic curve at the optimal operating point, in which “optimal” is in terms of minimising costs (C). “Costs” can be identified here as patient morbidity, where CFP, CFN, CTN and CTP represent the costs of false-positive, false-negative, true-negative and true-positive results, respectively. Here, it was assumed that CFP = CFN and CTP = CTN. Therefore, here S = ((1–P)/P), where P denotes the prevalence in the target population. : prevalence in study population. To use this table for a given patient from, for example, a department of respiratory disease where the prevalence of HP is nearly 35%, with a serological score of -0.43 (>-0.53) with discrete variables and 0.18 (>-0.78) with dichotomous variables, both serological scores indicate a diagnosis in favour of HP. To calculate scores, see table 3.