Finally, there are genetic factors. The blood coagulation system is an intricate cascade of about 20 proteins, all activating or suppressing each other. (Female hormones seem to increase proclotting proteins and decrease inhibitors.) A clotting protein variant called factor V Leiden, present in 5 percent of Caucasian women, resists inhibitor proteins. Having factor V Leiden bumps up DVT risk 35-fold when combined with taking the pill. Add air travel and age over 40 and you’re approaching a 50 percent chance of getting a clot. That’s why I was questioning the use of the pill by the pond-hopping 51-year-old Mrs. Watson, with her DVT-prone kin.
Clots can break off and eventually end up wedged in the vessels of the lungs, corking blood flow out of the right ventricle.
Though irritating and painful, DVTs aren’t the killers. Pulmonary emboli are. These are clots that travel and end up in the lung. (An embolus is a clot that travels.) Clots in the legs can break off from the wall of a blood vessel, course through the heart, and wedge into the great vessels of the lungs, corking the blood flow out of the right ventricle. A pulmonary embolus (PE) is treacherous because the symptoms mimic colds, rib-muscle strains, or the wheezing of an asthma attack—and there’s often a bigger one close behind. Such clots kill 200,000 people a year, often without warning.
The treatment for DVT is anticoagulation. The classic medication is heparin—a drug discovered almost a century ago—which requires continuous IV dosing. Newer versions like Lovenox can be injected subcutaneously once a day at home. In a patient with an uncomplicated leg DVT, it’s a reasonable plan.
“So can I go home now?” Mrs. Watson pleaded.
“How about we see how extensive it is first?” I countered. She lay back down.
Dr. Singh wheeled the ultrasound machine over. Pressing the probe along Mrs. Watson’s thigh, we followed the femoral vein down to the knee. Blood vessels look like black circles on the screen, but with gentle pressure, a vein should wink flat. If a clot is there, it can’t do that.
“It collapses nicely down to the knee,” I said. “No clot in the thigh.”
Mrs. Watson sat up. “Can I go now?”
“Well,” I hedged, “the clot probably goes from the knee down. That’s harder to see. The vascular technician is gone for the day. We can’t do a complete study until tomorrow.”
Dr. Singh and I stepped out of the room. “We could give her a shot of Lovenox and have her follow up with her doctor tomorrow, right?” he asked.
“Yes,” I replied. “Question is, does she have a silent PE? No respiratory symptoms now, but a number of DVT patients have them, and if she did, we’d admit.”
“Should we get a CT scan?”
“It’s a fair amount of radiation. Our suspicion is low, and the treatment’s the same. I’d hold off for now.”
Maybe it was the recent case of a 30-year-old on the pill who had flown from Paris and died of a massive PE, or maybe that calf just seemed too painful, but I decided to err on the side of caution.
“It’s best if you stay,” I told Mrs Watson. “They’ll do the formal ultrasound first thing tomorrow.”
Two days later, Dr. Singh found me. “Not just a DVT,” he announced. “Remember the cat allergy? The day after she arrived in London, she started wheezing. Told the doc there about her cat allergies. They’d never involved wheezing before, but he went with that and put her on steroids. Over the next few days it got better. Then she flew back to New York and the leg flared up. After we admitted her, the attending upstairs didn’t buy the allergy story. CT scan showed a PE.”
I smacked my forehead. “Of course. Fifty-one-year-old on birth control pills with family history of DVT flies to London and develops respiratory complaints.”
“Good thing we admitted her,” Dr. Singh said soothingly. “We’ll put her on a blood thinner for a few months. After that, we’ll check to see if she needs to continue. I guess her doctor will stop the pill now.”
“Yes,” I said. “It’s about time.”
