A combination model for predicting IPAH and CTEPH vs. controls using different cut-offs for IPAH (apelin-17 > 1,480 pg/ml, NT-proBNP >140 pg/ml, GDF-15 > 855 pg/ml) and CTEPH (NT-proBNP >305 pg/ml, apelin-17 > 1,270 pg/ml, GDF-15 > 1,220 pg/ml). The gene discussed is GDF15; the disease is idiopathic pulmonary arterial hypertension.