FAQ: When Should You Get a CT Scan? Can It Help Diagnose COVID?

Dr Sumit Ray, critical care medicine, Holy Family Hospital, Delhi, explains who should get a CT scan. Image used for representation.

(Photo: iStock)

As the rise in COVID-19 cases in India outpaces the healthcare system, the desperation to know more and try everything possible has gone up too.

With medical advice, tips, and recommendations flooding social media, it can be hard to sift solid facts from the husk. We've seen this with treatments like Remdesivir, Ivermectin, and plasma therapy.

But it's not just this, there has also been a surge in the indiscriminate use of CT scans to diagnose COVID. The catch, though, is that the cost of CT scans is not capped or moderated the way it is for other COVID tests, a factor that can turn its use exploitative.

Moreover, except in certain cases, not everyone who shows symptoms of COVID needs to get a CT scan done.

What is the truth about CT scans for COVID testing? When do you really need to get it done? FIT asks Dr Sumit Ray, critical care medicine, Holy Family Hospital, Delhi.

What is a CT scan, and does it help with COVID-19 detection?

According to the Mayo Clinic, CT — or computerized tomography — scans are a series of cross-sectional images created using multiple X-rays and computer processing.

CT scans typically provide more detailed information, not only about bones, but also of the blood vessels and soft tissues inside your body. They are used to detect internal injuries.

In patients of COVID-19, chest CT scans can help detect COVID-pneumonia (a sign that the infection has turned severe), and other abnormalities in the lungs related to COVID-19.

But, "diagnosing COVID is not its primary purpose," says Dr Sumit Ray.

In that case, why are CT scans being prescribed to diagnose COVID-19?

RT-PCRs are the most widely used mode of detecting the infection in a person, but questions have been raised about their accuracy.

Though RT-PCR tests are considered the 'gold standard' in COVID testing by healthcare experts, they are known to render false negatives every now and then.

False negative results occur when a person who is experiencing all telltale symptoms of COVID tests negative for the infection. This can be because of a string of different reasons we’ve explained here.

With RT-PCR tests, there is also the question of whether variants of the virus can slip through these tests.

The DG of ICMR, among other health experts, has ruled out this possibility, saying,

“RT-PCR test is gold standard, we measure two genes or more, therefore, there is no chance of missing detection of any mutant.”

Dr Balram Bhargava, Director-General, ICMR

There could also be other reasons for tests results showing false negatives. For instance, if the sample is not collected, stored, or transported properly, it could mess with the results.

"All tests historically have a certain amount of false negatives, and that is true of COVID tests too," says Dr Sumit Ray.

For this reason, experts may sometimes recommend getting a combination of RT-PCR, X-Ray, and CT scans done to rule out other illnesses.

That being said, not everyone who gets COVID has to get a CT scan.

“CT scans can help with diagnosis, but that is not the primary purpose of a CT, and it is important to know this because that way you can avoid a lot of CT scans.”

Dr Sumit Ray, critical care medicine, Holy Family Hospital, Delhi

"CT should be used to see the severity of the illness, and that too if the severity is persistent," emphasises Dr Ray.

When should you get a CT scan done?

Dr Ray talks about the importance of context when it comes to any medical treatment.

"CT scans too are only useful in specific contexts," and in the case of COVID, "this context is the severity of the infection," he says.

“There is no blanket guideline about whether CT should be done or not done. It will depend on a combination of factors including the doctor’s clinical judgement, the tests already done and also the patient’s requirements.”

Dr Sumit Ray, critical care medicine, Holy Family Hospital, Delhi

According to Dr Ray, "CT is to be used to gauge the severity of the infection and the level of support the patient will need."

"If the doctor suspects worsening of the condition, or suspects other conditions such as blood clotting in the lungs, fibrosis in the lungs."

In a hospital setting, according to Dr Ray, a CT scan may be required in case of:

• High grade fever persistent for over 6-7 days.
• High inflammatory markers.
• Worsening oxygen levels, and worsening breathlessness.

But even under these circumstances, he emphasises that a CT scan may not be required.

"The doctor should make the clinical judgement on the potential of the person to deteriorate," he adds.

What should you know before getting a CT scan done, if you have COVID?

To break it down further,

• A CT scan is just an imagery technique, and not a test.

This means that a chest CT scan can reveal certain chest abnormalities that may be a result of COVID, but these alone are not enough to diagnose COVID, like in the case of swab tests that are designed to detect a specific infection.

• CT scans can also show false negatives

As Dr Ray mentioned before, no test is foolproof.

This is especially true given that not all COVID patients will have abnormalities in the lungs and chest. Not having these abnormalities pop up on the CT scan does not rule out COVID either.

In fact, most patients of COVID will not have any abnormalities in the chest.

For this reason, he recommends treating patients with relevant symptoms as COVID-19 patients, no matter what the test results say, until definitive evidence is established.

• CT scans should be done under specific conditions only

As mentioned earlier, CT scans can be very helpful in getting to the bottom of why a patient's condition may be deteriorating, and should be done only in severe cases, taking the specific symptoms of the patient into consideration.

"In a OPD setting, very rarely would a patient need a CT scan," says Dr Ray.

(This was first published on FIT.)