This disclosure concerns improved capabilities for evaluating whether additional medical tests need to be conducted for a diagnosis of a pulmonary arterial hypertension (PAH) condition in a patient. The method includes determining that the patient is at rest and measuring a partial pressure of carbon dioxide in a composite gas, comprising: transferring an expiration from the patient's mouth to a carbon dioxide analyzer; measuring end tidal carbon dioxide (EtCO2) from each of a plurality of oral expirations from the patient; and calculating a composite EtCO2 value. The method further includes comparing the composite EtCO2 value to a range of stored carbon dioxide partial pressure values; generating a signal indicating whether additional medical tests need to be conducted in response to the comparing; and providing the generated signal to an indicator, the indicator adapted to respond to the generated signal to provide an output in a human cognizable format.