Capillary pCO2 helps determine IPAH diagnosis

Capillary pCO₂ (P_cCO₂) can be used to distinguish idiopathic pulmonary arterial hypertension (IPAH) from pulmonary hypertension due to heart failure with preserved ejection fraction (PH-HFpEF), research indicates.

The researchers, from Hannover Medical School in Germany, say that the finding could help reduce the number of misclassifications of the two conditions.

The team enrolled 99 patients with IPAH and 86 with PH-HFpEF. They found that at the time of diagnosis, patients in the PH-HFpEF group tended to have P_cCO₂ values in the normal range, at an average of 40 mmHg. However, in the IPAH group the average P_cCO₂ was significantly lower, at an average of 33 mmHg.

Receiver operating characteristics analysis suggested that P_cCO₂ may be helpful in distinguishing between the two conditions: a value of 36 mmHg was most accurate for this purpose, with an area under the curve value of 0.87.

The team found that measurement of P_cCO₂ provided relevant diagnostic information for 49% of their patients; a value below 34 mmHg excluded PH-HFpEF with a likelihood of over 90%, while a P_cCO₂ value over 41 mmHg was associated with a less than 10% probability of IPAH.

Writing in Respiratory Research, Karen Olsson and colleagues explain that, while classifying most patients with PH into one of the five subgroups for the condition is straightforward, it has become increasingly challenging to discriminate between those with IPAH and those with PH-HFpEF.

“This distinction, however, is of fundamental practical importance as the treatment of IPAH differs substantially from the treatment of patients with PH-HFpEF”, they note.

The authors say that invasive measurements used to diagnose IPAH and PH-HFpEF based on whether patients have pre- or post-capillary PH can give misleading results leading to misclassification.

“In the past, this problem was less evident as IPAH was originally considered predominantly a disease of younger women, and these patients are not at risk for developing HFpEF”, they write.

“More recently, however, IPAH is increasingly diagnosed in older patients, many of whom present with risk factors for developing left heart disease.”

Olsson and colleagues say that additional non-invasive variables, such as P_cCO₂ could be useful for distinguishing between the two conditions.

“Further studies are needed to determine the value of P_cCO₂ in the diagnostic work-up of patients with PH”, they conclude.

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