Why Is a V/Q Scan Needed for Pulmonary Hypertension?

If you have already been told you have high blood pressure in your lungs, it is completely normal to feel exhausted by the constant medical tests. You might wonder why your medical team is strongly recommending yet another imaging test—a V/Q scan (ventilation/perfusion scan)—when an echocardiogram or right heart catheterization has already shown that your pressures are high.

The short answer is that a V/Q scan is the preferred screening test to check if your pulmonary hypertension is being caused by old, chronic blood clots ^[1]. This specific condition is called Chronic Thromboembolic Pulmonary Hypertension (CTEPH).

Even though your doctors know your pulmonary pressures are high, they must determine the underlying cause. Idiopathic pulmonary arterial hypertension (IPAH) and CTEPH may share similar symptoms, but their treatment pathways are very different ^[2].

The Search for a Treatable Cause

When a fresh blood clot travels to the lungs (a pulmonary embolism), the body’s natural systems usually break it down over time, while blood thinners are used to prevent new clots from forming. However, in some people, these clots do not fully dissolve. Instead, they turn into permanent, scar-like blockages in the lung’s blood vessels, leading to high pressure and right heart strain ^[3]. You can develop CTEPH even if you do not remember ever having a blood clot in the past ^[1].

The most important reason to screen for CTEPH is that it has unique, highly effective treatments. For eligible patients, a specialized surgery called pulmonary endarterectomy (PTE) can remove the blockages and is potentially curative ^[3][2]. For those who are not candidates for surgery, there are other targeted options, such as balloon pulmonary angioplasty or specific medications, along with lifelong anticoagulation ^[2]. Because IPAH is treated primarily with medications that relax the blood vessels (vasodilators), it is crucial not to miss a CTEPH diagnosis ^[2].

Why a V/Q Scan Instead of a CT Scan?

You may have already had a standard chest CT scan and wonder why that is not enough. While CT scans are excellent for finding fresh blood clots, they can easily miss the old, flattened, scar-like lesions of CTEPH ^[1]. Even a specialized CT pulmonary angiogram (CTPA) can sometimes miss subtle chronic changes unless read by a CTEPH expert ^[4].

A V/Q scan takes a different approach. It uses a very low dose of radiation (inhaled and injected) to measure the actual flow of air (ventilation) and blood (perfusion) through your lungs. You should let your care team know if you are pregnant or breastfeeding, but the test is generally well-tolerated. V/Q scans are highly sensitive for detecting the specific “mismatched” blood flow patterns caused by CTEPH ^[5]. Because of this high sensitivity, international medical guidelines strongly recommend a V/Q scan as the primary screening tool for anyone with unexplained pulmonary hypertension ^[1][2].

What the Results Mean

• If the scan is normal: CTEPH is considered very unlikely ^[1][6]. However, a normal V/Q scan does not automatically prove you have IPAH; it simply crosses CTEPH off the list. Your doctor will still need to rule out other causes and confirm your pressures with a right heart catheterization ^[7].
• If the scan is abnormal: This does not immediately prove you have CTEPH or a fresh blood clot. Other lung conditions can also cause irregular scan results ^[8]. If your scan shows “mismatched defects” (areas that get air but no blood flow), you will likely be referred to a specialized pulmonary hypertension center. There, experts will use confirmatory imaging, like a CTPA or a pulmonary angiogram, to map out the blood vessels and discuss your treatment options ^[7][2].

While “scan fatigue” is a very real and valid feeling during the diagnostic process, the V/Q scan is a vital safety step to ensure a potentially treatable condition is not overlooked.