Five Quarts_ A Personal and Natural History of Blood - Bill Hayes [62]
Yes, I see what looks like a drawing of venetian blinds—strips of flattened DNA, I gather, nodding. But Dr. Winger has already moved on. He draws two graphs that look like sales curves.
“With each cycle, we get a doubling of just this region here and it amplifies geometrically . . .”
Dr. Winger’s verbal momentum is gaining speed, yet I am utterly lost and feel only a little regret at pulling out his power cord. I ask for the layman’s version and he obliges, although, at first, it is still more of the Dr.-Layman-Ph.D. variety. But finally, he breaks it down this way: They take a sample of blood—less than half a teaspoon—then remove a single fragment of DNA from an HIV particle and clone, or “amplify,” it. Using a mathematical formula, they then calculate the number of viral particles, or “copies,” originally present in the sample. This number is an accurate fraction of the total amount in the bloodstream. Okay, that makes sense, I think, but Dr. Winger cannot resist a big textbook finish: “There’s a rule of thumb that the number of cycles required is inversely related to the log of the starting copy number.”
What’s not lost on me is the impact these results will have in the doctor-patient sit-down. There, it’s not a number you hope to see but a word. When fewer than fifty copies are found in a patient’s blood, the Q-PCR test finding is labeled “undetectable.” Fifty copies may sound like a lot, but this is actually an infinitesimal amount of HIV. The take-home message is, if your virus is undetectable, your drug cocktail’s working and viral activity is at a virtual standstill. Though its diagnostic meaning is unambiguous, the casual use of the word has caused problems. When doctors announced in 1997, for example, that Magic Johnson’s virus was undetectable, many fans took this to mean that the former Laker no longer had HIV. It didn’t help that his wife, Cookie, declared in an Ebony magazine interview that Magic had been “cured.” His doctors “think it’s the medicine,” she’s quoted as saying. “We claim it in the name of Jesus.” But no miracle had occurred. In fact, after Johnson later neglected to take his meds during a long vacation, his viral load shot back up to detectable levels. My partner Steve has put his own spin on this semantic confusion: Undetectable is a lot like the Invisible Woman from the Fantastic Four—just because you don’t see her doesn’t mean she’s not there.
Dr. Winger explains that, of course, PCR testing has other applications outside of HIV care. It serves an essential role in forensics science, for instance, by isolating the DNA “fingerprint” of blood or tissue evidence found at crime scenes. And the killer is . . . !
At this point in the tour, I’m realizing how loudly he and I have to talk to be heard over the racket made by these two machines. (What must this place sound like in the middle of the night, when all the machinery is in high gear?) We stand before the apparatus that is used to isolate the DNA molecule. Though it’s not much larger than a toaster oven, it sounds like a dryer filled with tennis shoes. The thumping, Dr. Winger explains, is made by a piston that pushes cell particles through an interior tube at a pressurized weight of more than three thousand pounds per square inch. I mouth wow back to him.
We now move on to other noises. Loudest of all are two liquid nitrogen tanks. These are powered by individual generators that are doing a good imitation of cement trucks. The tanks, which resemble a large pair of bongos, are where tissue and cell cultures are preserved. “They’re cold as hell,” Dr. Winger specifies. “Minus 195 degrees Celsius.” As he unlatches one of the lids, fog-like vapor overflows. “Put your hand down in there,” he urges me, flashing a triangle-shaped smile. “But don’t touch the sides!” I’m reluctant—I’ve seen The Empire Strikes Back too many times not to flash on Han Solo being frozen in carbonite—but I summon the wherewithal to dip my index finger in partway. “Very, very cold,” Dr. Winger chirps. “Exceptionally cold.”
Continuing