Poor testing, dosing dog fetomaternal bleeds

Among FMH cognoscenti, there’s agreement that despite troubling data about Kleihauer-Betke’s unreliability, most players are unaware there’s a problem with the test.
As noted earlier, clinicians aren’t demanding flow cytometry. OB-GYNs “all think KB is accurate,” says Dr. Moise.

“There’s not a lot of attention or understanding that this is even an issue,” agrees Dr. Delaney, who is also a TMRC member and one of the commentary authors.

Kleihauer-Betke can also be done quickly, no small consideration given that physicians have a short window—72 hours from when a woman delivers, according to standard practice—in which to administer Rh immune globulin. Flow cytometry, on the other hand, wouldn’t necessarily be available when pregnant patients are most likely to need it—that is, 24/7. “I think that’s another reason why KB has held on,” says Dr. Moise, speaking with the experience of someone whose seen more than his share of weekend births and mothers eager to get home quickly. “It can be done in most hospitals whenever it’s needed, even though they’re not very good at doing it.”

While that has the ringing endorsement of serving tuna noodle casserole for dinner—sure, go ahead and open that can of cream of mushroom soup, but is it really the healthiest meal to prepare?—it can be hard to make a better choice.

Even those who see the problems concede change could be a long way off. Listening to them explore the issue is a fascinating exercise, like observing the same attorney argue both sides of a case. Data and experience show that KB should be dropped, they say. On the other hand, flow is an expensive procedure. Not every lab has the deep pockets or expertise to set it up, especially for such an uncommon event. Indeed, Dr. Delaney, whose blood bank has had several conversations with the flow cytometry lab about doing the test, admits it’s been difficult to make the case. The numbers just aren’t there. “Bringing in a test is a medical and a business decision,” she says.

Other numbers argue against moving to flow as well. In clinical practice, Dr. Sandler notes, any time an Rh-negative woman delivers an Rh-positive newborn, she automatically receives one vial of Rh immune globulin, even if there’s no evidence of fetomaternal hemorrhage. If there is such evidence, it’s standard to add one vial of RhIg into the calculation to ensure a very wide margin of safety. Thus, even with the KB’s limitations and calculation errors, the Rh immunoprophylaxis failure rate is almost imperceptible. Ask a physician about the efficacy of current practice, says Dr. Sandler, and the response will invariably be, “I’ve never seen a case that failed.” The failure rate, he says, is roughly one in 10,000; in those cases, the fault is thought to lie with failure to give the injection, not failure of the lab test or the calculation.

In short, the current system, for all its flaws, is, in many regards, successful. But when things go wrong, they go really wrong.

Dr. Moise recounts the case of a recent patient, at regular term, who had an abruption and a 130-mL bleed, which was confirmed by multiple KB tests. “It was confusing to me, because the baby looked fine,” he recalls. For its part, the blood bank couldn’t figure out how much RhIg to give the patient. “They were scared to give the IV prophylactic—they hadn’t done that before for a massive bleed. They were just out of their league,” says Dr. Moise.

“I get calls from blood banks all the time, and from perinatologists, saying, ‘We don’t know what to do.’ People are at a loss,” Dr. Moise says. If the events are rare, that also means when they occur, people rarely have answers.

In an ideal world, every hospital that delivered babies would make accurate calculations and use flow cytometry. But Plato is not in charge here; Candide is. So while FMH experts consider using a more complex, more expensive test, one with slower turnaround times, to cover rare situations and fix problems that most people don’t even realize exist, what, realistically, is the next best thing?

Dr. Moise would like laboratories to give better guidance for determining when enough RhIg has been given after a large bleed. When Dr. Moise gives lectures to obstetricians, he likes to tell them that current recommendations round off the calculation to the nearest decimal point, “then add one to grow on,” he says. “They all get a kick out of the ‘science’ of how much Rh immune globulin to give. But you’ll see very poor recommendations in the obstetrical literature, on what to do.” As far as he’s concerned, “That’s another hole in the system,” along with poor calculations and poor testing methods.

Likewise, Dr. Moise says clinicians would benefit from recommendations on when to repeat a patient’s anti-D titer after she’s received multiple vials of RhIg.

At the very least, he says, labs need to refine their calculations. “It’s one of my pet peeves, when labs make the calculation based on a maternal blood volume of five liters every time. Obviously we know all women don’t have five-liter blood volumes.” Why not just use the dose calculator? he asks.

Dr. Sandler, looking beyond hospital labs, would like to see large reference labs step up. “There’s a terrific opportunity to capture an entire community’s flow cytometry for fetomaternal hemorrhage,” he suggests.

So far reference labs haven’t taken the bait. Dr. Brecher says he and his colleagues at LabCorp haven’t discussed marketing the test on their own. “In the absence of significant demand from clinicians or a practice guideline that would favor it, we would be unlikely to see adoption even if we introduced the test.”

Dr. Sandler wonders if the demand is low because the referral channels for FMH testing aren’t as well established as they are for, say, viral testing. The first step, a screening test, typically is done at a blood bank; the sample is then sent to a hematology laboratory for the acid elution test. Perhaps, Dr. Sandler theorizes, “We’re somewhere in a crack between the blood bank and the hematology laboratory, neither of which are major sources of referrals to reference labs.”

Moreover, he continues, switching testing to a reference lab could be an unwelcome change in routine for some, regardless of how fraught that routine is. Sending samples to a reference lab is another way of saying that the sample has left the building, taking with it the hospital’s ability to be sure RhIg is injected within 72 hours. “It’s easy to understand how some decisionmakers might say, ‘We have a patient care deadline that I have control over now that’s very important, and I’m concerned about losing control over this chain of the lab sample, the lab test, the injection. I don’t want that to happen.’”

Patient advocacy groups, so important in other diseases, are unlikely to push for change. FMH is not front and center in most patients’ minds; it doesn’t have the apparent urgency of, say, a cancer diagnosis. It’s not about the current pregnancy; it’s about a potential problem with a future pregnancy, which isn’t going to be uppermost in the minds of women currently busy with a newborn. “An occasional woman who’s Rh negative, who’s going to get a shot, doesn’t present much of a lobbying group,” Dr. Sandler says.

Reference labs are more likely to respond if there is a mandate to require a better method, says Dr. Brecher. The push could come from major organizations such as the CAP, AABB, and ACOG.

Even then, the push would have to come from on high. It would not be a grass-roots effort, Dr. Moise says. “An obstetrician might be faced with this a couple times a year, so their interest in having a national guideline is not going to be very profound.”

But, as he points out, there’s no denying FMH can be a profound problem for the patient when it happens to her, and for those involved in her care. “It’s like teenage pregnancy—until it happens, no one thinks it’s going to happen to them.”

Karen Titus is CAP TODAY contributing editor and co-managing editor.