The PAH risk calculator is based on the DETECT algorithm. Here we describe how the algorithm works using nomogram-type illustrations.

For Step 1, the points for each variable can be assigned by drawing a vertical line from the measured value of that variable to the points’ line. All variables contribute points irrespective of the measured value; e.g. even a negative serum anti-centromere antibody (ACA) will contribute 50 risk points. If one of the six values is missing, the total score can be calculated with only a minor impact on the model performance. In this case the missing variable is assigned 50 points, (except for the missing variable current/past telangiectasias, which is assigned 65 points). The Step 1 total risk score is calculated by adding together the points for each variable. If the Step 1 total risk score for your patient is greater than 300, referral for echocardiography is recommended.

For Step 2, the points for each variable (i.e. the 2 echocardiography variables and the Step 1 total risk score) are assigned by drawing a vertical line from the value of that variable to the points’ line. The values for all Step 2 variables are required to calculate the Step 2 total risk score. If TR velocity cannot be determined because no TR is detectable upon echocardiography, 10 points should be assigned for TR velocity. The Step 2 total risk score is calculated by adding together the points for each variable. If the Step 2 total risk score for your patient is greater than 35, referral for right heart catheterization is recommended.

The algorithm cannot be reliably used if more than one of the six variables in Step 1 or any of the variables in Step 2 is missing (if TR velocity cannot be determined because no TR is detectable upon echocardiography, this does not count as a missing variable).