Chest X-ray and Chest CT Critical to Early Diagnosis of TB

March 22, 2021
Whitney J. Palmer

Decline in number of TB cases is slowing in the United States, making timely identification critical.

Using chest X-ray or chest CT scans to image the lungs of patients who have symptoms suspicious of tuberculosis can expedite diagnosis, potentially limiting transmission of the disease, a new study has found.

While tuberculosis (TB) is rare in the United States, recent data indicates that the pace of the decline in cases is slowing, and the number of TB-related deaths has not consistently followed the same downward trend. That makes timely identification of the disease vital, said a team of investigators from Harvard Medical School.

However, the average time from a first doctor’s visit to diagnosis is around 24 days with delays ranging from 10 days to 45 days and rising up to 250 days.

“The delays we found would be concerning under any circumstances, but they are unacceptable in a well-resourced health care system, such as the United States,” said senior investigator Maha Farhat, M.D., MSc, assistant professor biomedical informatics in the Blavatnik Institute of Harvard Medical School and pulmonary medicine physician at Massachusetts General Hospital.

Farhat’s team published their results Monday in The Lancet Infectious Diseases.

Based on their findings, the team determined that diagnosis delays are not only linked with a greater likelihood of disease transmission between household members, but it is also associated with a risk of greater disease progression. They did not set out to determine why the delays occur, but they hypothesized that TB frequently goes un- on under-recognized because providers simply are not as familiar with it here in the United States.

“Our findings point to the key importance of continuing education of providers. We found several factors associated with delays and faster diagnosis,” she said. “This tells us that delays are modifiable and preventable.”

For their study, Farhat’s team examined 18.9 million medical insurance claims from privately insured patients over nine years from 2008 to 2016. Of that group, 3,389 people had diagnostic codes suggestive of TB, and 738 eventually received a positive diagnosis.

A small amount – 9 percent – developed respiratory complications, but these issues were more common among patients who had slower diagnoses. Those with delays of roughly 32 days developed one or more complications, including irreversible lung damage, collapsed lungs, fungal lung infections, and spitting blood. But, patients who only had a 23-day delay did not.

Alongside the diagnostic delays, Farhat’s team also looked at TB transmission. Among the 456 patients with active TB, 177 had another household member with a latent case. Overall, the team reported, of the 1,026 household members who lived with study participants who had active TB, more than 25 percent became infected.

The team did find that patients who presented with three or more suspicious symptoms were more likely to receive a prompt diagnosis. Overall, physicians were apt to call for chest X-rays or chest CTs, as well as a molecular TB test, to identify the cause of the problem, they said.

Consequently, the high TB transmission rate and the risks of disease progression that accompany diagnostic delays point to the urgent need for imaging when patients present with suspicious symptoms, the team said. In this instance, over-testing is the safe option because an X-ray or a molecular test is an inexpensive way to pinpoint this infectious disease.

“If you have a patient with cough, fever, shortness of breath, especially if they were born abroad or are an older individual, then you should be ordering a chest X-ray early and, if abnormalities are seen, a TB nucleic acid amplification test,” Farhat said. “Yes, these are non-specific symptoms, but the key is to think about TB as a possibility and to remember that it is still present in the United States.”

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