New user and AST post Rhogam question

[gmeversole]

Hello,

I'm a new guy and am glad to have found this site. I have a question which perhaps I ought to post to a more proper forum; but until I figure this out, I will ask it here.

In what percentage of cases is an AST postive after standard Rhogam injection? On average, what is the longevity of a measurable AST at whatever titre for anti-D after injection. IgG half-life is about three weeks, but over what time interval are our tests sufficiently sensitive to pick up a titer? I would assume all answers would be tempered by the presence of MFH of varying severity which might account for loss of the passive anti-D in the serum. And, lastly, is anyone really looking at the AST to help determine if additional Rhogam is necessary (in an antepartum bleed situation, i.e., within three days of the initial injection to see if another injection is called for)? Nothing like a succinct question on my first foray, huh?

[donellda]

Hi! Welcome to Bloodbanktalk! We pretty well have a set protocol for administering Rhogam to our patients. If the antibody screen is still postive from the most recent injection of Rhogam, we still get post partum specimen (if baby is Rh positive) for a fetal screen. If the fetal screen is negative we administer one vial. If it is positive we send it for a fetal hemoglobin stain to determine if more additional vials are required. Maybe there is someone who can answer the rest of your questions.

[John C. Staley]

OK I give up. What are you referring to as AST? I've been around for a long time and I can't figure this one out. Just had a thought, could it be Antibody Screening Test? If so, that's a new acronym for me.

If that is what you are referring to a lot depends on the test system you use. We see lots more than we want to with our ABS2000. We do a mini panel to confirm anti-D and confirm the patient had received a recent dose of RhIG. Recent can be as much as 3 months prior. If so, we report it as anti-D with a comment that the patient had received RhIG and the date if available. Then we go about giving her more based of the FMH testing.

I assume your concern about the antepartum bleed after the RhIG is that it gets bled out so it can't do the job. Good question, never really thought about it. So you do an antibody screen and it's postive for anti-D. Is that good enough? If it's negative do you give more? I think all this would be up to the physician to consider and I doubt most of them would ever think of it. Another thought, the RhIG is an IM injection so a rapid bleed should not lose that much and the antibody screen would still not tell you very much.

Sounds like a great SBB student project to me.

[donellda]

I took AST as antibody screen test and MFH as maternal fetal hemorrhage. There are some interesting points here to ponder!

[gmeversole]

Didn't mean to be so cryptic. Yes: antibody screeing test and maternal fetal hemorrhage. This line of questioning began because a local OB/gyn questioned the validity of our antibody screen on a second trimester patient with a second vaginal bleeding event (not a threatened pregnancy loss). She had given the young lady a Rhogam injection and ordered the screen three days later to see if she should give another injection. The screen was negative. She felt that was impossible and also wanted a way to differentiate passive from alloimmunization. Well, first of all the screen would have to be positive! If it were, and if it were low titer, one might presume passive. If it were higher, one could do DTT treatment. But all that is moot. So, the essence of my question was how often is the screen negative in the few days post injection; I have no reason to believe we have an analytical problem.

[Mabel Adams]

I took MFH for massive fetal hemorrhage. Glad you clarified.

OK, how could a pregnant patient bleed enough to bleed out the RhIg without needing a blood transfusion and/or losing the baby? I suspect the docs that want to order this think that the anti-D is used up--that it attaches to fetal cells in the mom's circulation and is removed.

I have heard (Dr. Mary Jo Drew, I think) that it is never indicated to do an antibody screen after giving a dose to see if it is still there or there strong enough etc. If they're that worried, just give the second dose!

As to why it was not detectable in 3 days: Was it actually given? Is the patient large and/or very muscular or very sedentary so that the IM dose would either be diluted in a large blood volume or still making its way into the circulation at that early date? I bet a pharmacist could tell you in general about IM drugs moving into circulation.

When I had a patient with anti-D that was given 28 wk RhIg "because it was routine", I hunted all over for data on how fast it was absorbed into the blood from the muscle and couldn't find diddly. (Shoulda thought of the pharmacist then.)

You might ask the doc what she thinks would happen if a fetus of that age lost 30 ml of blood transplacentally. At 20 weeks gestation, that is about the baby's whole blood volume so the baby could bleed to death in the early 2nd trimester without the mother needing a second dose. Someone with perinatolgy experience could probably give you blood volumes of babies at different gestations to help put this in perspective. Maybe an ultrasound would be more useful than an antibody screen. Of course the baby can keep making new red cells so a slow leak over time could accumulate I suppose.

We had an OB doc that did Kleihauers on every *** bleed for the first 5 years she was here. Not one was ever positive. Doesn't mean it couldn't happen, but it certainly isn't the most common cause.

I think I strained the "quick reply" box.

[johna]

As a former employee of Ortho Diagnostic Systems Inc. (the "Rhogam" people) the information that we were given is that there is no evidence to suggest a correlation between the post-injection presence of anti-D and the effectiveness of the product. As far as I know nothing has changed since then to suggest otherwise. Another problem with using the antibody screen as an index is that there are so many different methodologies for antibody screening that whether anti-D is detected or may be totally dependent upon the protocol being used.

On a side note the rule of thumb as far as I know it has always been that if the patient has not received Rh immune globulin within a six month period prior anti-D being detected then the anti-D is not due to the Rh immune globulin.

[AMcCord]

There was a time - long ago - before fetalscreens, when our OB/GYNs wanted the antibody screen to see if they should give more RhoGAM post delivery. These were drawn 24 hours after the first dose was given. As I recall, approximately 20-30%, (rough, rough guestimate) of these patients got another RhoGAM because their screen was negative (tube testing, of course). A few even got a third dose before we got a positive screen (and they were usually larger size women). Anybody delivering twins automatically got 2 vials to start.

We argued until we were blue in the face about the use of the screen for this purpose, but they had heard it at a conference - GOD had spoken! We started doing fetalscreens when the kits became available and reported them in parallel with the antibody screens. After about 18 months, it started to sink in with them that the fetalscreens were all negative. Imagine that! They asked for information about the fetalscreens (and maybe heard something more at a conference) and suddenly, no more antibody screens were ordered to determine RhoGAM dosage.

So, in answer to your question finally, you can see a significant number of women with a negative antibody screen doing it the way your doc is asking you to do it - depending on your method. You may also see a 4+ reaction within a few hours post dose with gel. Maybe a little education by your medical director would be helpful (or not!).

AMcCord

[Jane]

When we used the tube method with LISS for antibody screens, we never (almost never) picked up Rhogam in the screen. Now that we use gel, we pick it up (almost) all the time. Sorry if someone already said this and hope it helps.

[bbbirder]

I think part of the problem with RhIG injections relate to some ACOG recommendations. The January, 2007 issue of AABB news had a Q&A page about some of this. ACOG recommends if there is an event withing 3 weeks of injection that 'if an indirect antiglobulin test result is positive for anti-D, not additional RhIG is necessary.' But, as the Q&A says there is no data to support this recommendation.

Do the fetal screen or fetal cell stain initially, then you should know if you have given an adequate dose.

We have also had OBs question a negative antibody screen after an injection. Who knows? Maybe it was just doing it's job. Maybe the woman is really a D-variant and absorbed it herself? (We no longer do weak D testing routinely.)

We detect what is probably passive anti-D for 5 months or so, when using gel.

Mabel, about fetal bleed volumes... there is a post on the CBBS web page about 'chronic FMH'... amazing how much blood can be lost over time.

I am rambling on...

Linda Frederick

[Mabel Adams]

http://www.cbbsweb.org/enf/2003/fmh_antenatal.html

Here is a link to the CBBS page noted above. Is there someone that could see that this info gets into the next Tech Manual near (or in place of) the "20 weeks gestation" entry?

[LESIZE]

I am also a new member. Interesting question ? Never gave it much thought RHIG is administered if a positive IAT within 3-5mos it is indicated as passive anti-D due to RHIG.

One quick ? can you help and tell me how are messages posted? Would like to know

Thanks,

ES