Sudden death: NBC anchor David Bloom’s death in Iraq was not combat-related. He suffered from pulmonary embolism. (Reuters)

Most patients remain oblivious of the danger, and some doctors don’t even suspect it. But a new study suggests that life-threatening blood clots in the lungs may be a lot more common in India than assumed by doctors.

The condition, called pulmonary embolism (PE), remains underestimated in India and doctors may not be doing enough to prevent its occurrence even when they can, say experts at the Sir Ganga Ram Hospital (SGRH) in New Delhi who conducted the study.

A PE usually results when a clot in a deep vein in the leg fragments and gets carried into one of the lungs where it grows in size and blocks blood supply to the lung. “It’s like a lung attack, something analogous to a heart attack,” says Dr Rajiv Parakh, a senior doctor at the SGRH. “And without quick treatment, it can be lethal to the patient.”

A clot in the deep vein of the leg ? called deep vein thrombosis ? has many risk factors. People who have been advised bed-rest that extends beyond a week, patients who have undergone surgery lasting more than an hour, women on hormone replacement therapy or on oral contraceptive pills, and passengers who’ve spent several hours immobile on intercontinental flights may be at risk of developing deep vein thrombosis. Those who have undergone knee operations or hip transplants are also at risk of developing deep vein thrombosis and PE.

The standard symptoms of the former include a swelling of the leg, a noticeable warmth and redness of the leg, and pain that gets worse when the patient is standing or walking. Doctors say that the risk of deep vein thrombosis deteriorating into PE is higher when the clot forms in a deep vein above the knee. “A 1.5-cm clot can grow in size in the blood vessel of the lung and obstruct blood supply,” says Parakh.

He and his colleagues studied 1,552 patients who visited the ‘swollen leg’ clinic at the SGRH over a three-year period. Among the patients with the leg symptoms, 251 also had symptoms that indicated PE ? breathlessness, chest pain, chest discomfort and coughing with blood. Collaborating with the nuclear medicine specialists at the hospital, Parakh diagnosed deep vein thrombosis in 744 patients.

In investigating the patients, Parakh and his colleagues used a technique called radionuclide venography to search for clots. In this a radioactive material is injected into a vein in the foot of the patient, and it is tracked via x-ray scans as it moves up through the legs, abdomen and into the lungs.

“The technique takes less than 10 minutes, but allows us to determine the total clot load in the body,” says Parakh. “The technique allows us to distinguish between patients with deep vein thrombosis who can be treated as outpatients and monitored, and those who have pulmonary embolism and would probably need to be hospitalised.”

In a research paper accepted for publication in the journal Clinical and Applied Thrombosis and Haemostasis, the SGRG doctors say they have detected a surprisingly high prevalence of PE in patients with deep vein thrombosis.

The study indicates that the traditional notions that the prevalence of pulmonary embolism after deep vein thrombosis in India may be lower than in the West should be abandoned.

According to Parakh, radionuclide venography, which can help measure the total clot load in the body, will be a useful technique not just for detection of PE but to monitor the response of patients to treatment as well.

“There is need for more doctors to think about the possibility of deep vein thrombosis and PE when they are dealing with patients who’ve faced one or more of the risk factors associated with these conditions,” says Parakh. “Standard ways to reduce the risk includes administering patients blood-thinning agents.”

One out of two patients with potentially lethal PE at the SGRH had no symptoms. But the researchers say that they examined a group of patients who visited the hospital because they had pain in the legs or some other symptom associated with deep vein thrombosis. Up to 75 per cent of patients with PE may not have any symptoms and need to rely on diagnosis for treatment.

The findings from the SGRH study are in line with the figures from the US which show that over 60 per cent of patients with deep vein thrombosis may have PE as well and more than half of patients with PE have no symptoms.

The study at the SGRH isn’t the first to suggest that doctors need to think about the risk of PE more often when dealing with their patients.

Two years ago, a study by some doctors in Calcutta showed that nearly one out of two critically ill hospitalised patients did not receive blood-thinning drugs although they needed the therapy, because they were at risk of developing PE.

The study, published in the Indian Journal of Critical-Care Medicine, covered several participating hospitals in Calcutta and showed that of the 100 patients who should have received the therapy to reduce the risk of PE, only 44 got it.

The doctors who conducted the study say apprehensions about bleeding may be among the factors that make doctors wary about prescribing blood-thinning agents for patients.

But, according to them, recent studies have shown that the risk of significant bleeding is negligible and it outweighs the benefit of preventing PE.