If you’re a smoker, you know by now how dangerous tobacco can be to your health. You also know how addictive cigarettes are, and how hard it is to kick the habit — especially if you’re still healthy. But what if doctors could tell you, with a simple test, that your lungs were already breaking down and on the path toward emphysema? Would it help you stop smoking then?
That’s what researchers at Weill Cornell Medical College are hoping. They report on a new blood test that could detect the earliest signs of emphysema, the lung disease in which the tiny air sacs in the lung tissue fall apart, leaving gaping holes that make breathing difficult, and eventually, impossible. Smoking is a leading cause of emphysema, but because it’s a progressive condition, many smokers can go years before getting short of breath. And once emphysema occurs, it can’t be reversed: when air sacs are destroyed, they are gone for good and can’t be rejuvenated.
So picking up the first signs of disease could help smokers to stop smoking, and therefore stop the breakdown in its tracks. Dr. Ronald Crystal, chairman of the department of genetic medicine at Weill Cornell, decided to look for a blood-based sign of emphysema after he realized the only way to assess lung function was with a CT scan, which exposes the patient to radiation, and which can be expensive. It turns out that when endothelial cells, which make up the air sacs in the lung, break down in the body, they release telltale signs of their death, in the form of microparticles that they shed into the blood. Crystal’s team devised a test for these endothelial microparticles (EMPs) and decided to test whether they could be a good marker for lung function.
Indeed, they were. After bringing 92 smokers and nonsmokers into the lab, he put them through two different tests of lung function. The more general test, or spirometry, measured how much air the participants could expel in a single breath, to determine how well their lungs functioned. Most physicians include this test for their smokers in the annual physical.
Then the scientists asked the volunteers to take a more sophisticated test that only specialists conduct when they suspect some sort of respiratory or lung disorder. This test provides a more detailed picture of lung function, specifically of how well the air sacs that are first affected by emphysema are working.
When Crystal compared the results of the two tests with the participants’ blood levels of EMP, he found that 95% of smokers with normal spirometry results but low air-sac function had elevated amounts of EMP.
“This would be the guy outside the building who smokes cigarettes, feels fine and goes to this doctor and is told his lungs are normal,” says Crystal. “What he doesn’t know is that he may be developing emphysema.”
Crystal’s team found that blood levels of EMP correlated well with lower air-sac function, suggesting that the blood test could be a useful early indicator of the disease. While emphysema can’t be reversed, it can be stopped, and there is evidence that when smokers are confronted with evidence of lung disease, they are more likely to quit smoking. “A useful analogy is the smoke alarm in your house,” says Crystal. “When it goes off, it doesn’t mean 100% that there is a fire, but you better check. This blood test is a smoke alarm for a potential fire in the lung. It’s a wake up call that says look, we have real evidence here of real damage going on in your lung and you better stop smoking.”
Before the test can be used more widely, however, it needs to be repeated and validated with a variety of different smoking and non-smoking populations. One important question those follow-up trials will address is whether other normal or disease processes can contribute to elevated EMPs in the blood. It’s known, for example, that high blood pressure and diabetes can push levels of these particles up, but Crystal says he also conducted tests that strongly indicate the EMPs in his study were primarily shed by the air sacs. The tiny blood vessels in the lung that nourish the air sacs are abundant in an enzyme that was also prevalent in the EMPs Crystal found in his study volunteers.
Until the test is validated, the results only strengthen the evidence for how harmful tobacco can be on the delicate architecture of the lungs. And even if the damage can’t be reversed, alerting people to the first signs of emphysema could help alleviate some of the burden of future disease. “If we had a test to tell you that you’re developing early emphysema, that your lung is beginning to fall apart, hopefully that will be helpful in convincing people to stop smoking,” says Crystal.