Can someone explain Rhogam usage?

[dendrites]

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Can someone explain Alloimmunization? Are all Rh negative mothers given Rhogam at 28 weeks? Then, if they baby is Rh + they are given Rhogam again?

Does that mean any mother that has taken Rhogam will test + for antibodies?

 

[Vigil]

Mom has baby No. 1.
Mom is Rh-, baby is Rh+.
During gestation, mom develops Rh+ antibodies. Rhogam not indicated for first pregnancy.
Baby No. 1 is delivered no complications and no hemolytic disease.

Baby No.2 comes along, is also Rh+.
Mom is immunized with Rhogam to suppress creation of anti-rhD antibodies which will attack fetus.
Baby is delivered. Success, no hemolytic disease!

Subsequent pregnancies consider rhogam.

 

[st0w]

Can someone explain Alloimmunization? Are all Rh negative mothers given Rhogam at 28 weeks? Then, if they baby is Rh + they are given Rhogam again?

Does that mean any mother that has taken Rhogam will test + for antibodies?

No, if an Rh- mother tests positive for anti-D antibodies, then she was not dosed at the appropriate time(s) or she was dosed with an insufficient amount. The whole purpose of RhoGAM is to *prevent* antibodies from forming. Once the immune system sees the antigen and creates the antibody, it's there for good.

RhoGAM is basically just anti-D IgG antibodies. Its function is to prevent the mother's immune system from recognizing and forming antibodies against Rh+ RBCs. I always thought of it like RhoGAM is blocking off all the Rho(D) antigens so the mom's immune system can't see them, but according to an FDA document, it's not so simple and we don't exactly know how it works. (http://www.fda.gov/downloads/biolog...blas/fractionatedplasmaproducts/ucm119475.pdf)

As far as I'm aware, all Rh- mothers who are having a child with a father who is unknown or Rh+ will receive it at 28 weeks and at delivery (as well as any unforseen events that potentially could result in maternal-fetal blood mixing). Of course, if the father is also Rh- then it's a moot point. There are more detailed dosing guidelines in that FDA document.

 

[st0w]

Mom has baby No. 1.
Mom is Rh-, baby is Rh+.
During gestation, mom develops Rh+ antibodies. Rhogam not indicated for first pregnancy.
Baby No. 1 is delivered no complications and no hemolytic disease.

Baby No.2 comes along, is also Rh+.
Mom is immunized with Rhogam to suppress creation of anti-rhD antibodies which will attack fetus.
Baby is delivered. Success, no hemolytic disease!

Subsequent pregnancies consider rhogam.

I don't believe that is correct. The purpose of RhoGAM is to *prevent* sensitization, not treat it once it has already occurred. In the case you describe, the mom is sensitized in the first pregnancy and it's already game over.

RhoGAM is only indicated for use in non-sensitized, Rho(D)-negative mothers. (See the above FDA document.)

 

[dendrites]

The reason im asking is because I had a pt that was Rh- but tested positive for antibodies. Her baby was Rh - also. The attending said that these antibodies were from the administration of Rhogam in a previous pregnancy. [How do you differentiate btw Rhogam antibodies and antibodies caused by alloimmunization]

Also, when they say a titer of greater than 1:16, what does this exactly mean?

Thanks

 

[armybound]

The reason im asking is because I had a pt that was Rh- but tested positive for antibodies. Her baby was Rh - also. The attending said that these antibodies were from the administration of Rhogam in a previous pregnancy. [How do you differentiate btw Rhogam antibodies and antibodies caused by alloimmunization]

Also, when they say a titer of greater than 1:16, what does this exactly mean?

Thanks

A titer has to do with concentration and dilution. Assume there's some certain amount of antibody required to turn a test positive. To get a titer, you take your patient's sample (blood, for example) and you dilute it.. 1:2, 1:4, 1:16, 1:32... so on and so forth, to see if the test is still positive. If the test is still positive when you dilute it to 1/16th of its original concentration, that must mean there's a pretty good amount of antibody in the serum. That's the general idea behind a titer, anyway.

How far postpartum was your patient? I'm pretty sure they're cleared from the body fairly quickly, like within 6 months.

 

[mjl1717]

Can someone explain Alloimmunization? Are all Rh negative mothers given Rhogam at 28 weeks? Then, if they baby is Rh + they are given Rhogam again?

Does that mean any mother that has taken Rhogam will test + for antibodies?

Great question!

 

[dendrites]

A titer has to do with concentration and dilution. Assume there's some certain amount of antibody required to turn a test positive. To get a titer, you take your patient's sample (blood, for example) and you dilute it.. 1:2, 1:4, 1:16, 1:32... so on and so forth, to see if the test is still positive. If the test is still positive when you dilute it to 1/16th of its original concentration, that must mean there's a pretty good amount of antibody in the serum. That's the general idea behind a titer, anyway.

How far postpartum was your patient? I'm pretty sure they're cleared from the body fairly quickly, like within 6 months.

she was 1 day post partum

 

[dendrites]

Ohhh maybe she was antibody positive from the Rhogam given at 28 weeks.

How do you tell if the antibodies are from Rhogam or from isoimmunization?

 

[SoDakMLS]

A woman who receives RhIg during pregnancy DOES have a positive antibody screen which when worked up looks just like a naturally produced Anti-D antibody. The practical way of discerning between the two is to check the chart for RhIg administration during the current pregnancy.

Once a woman develops a natural Anti-D antibody, RhIg is not indicated and pregnancies must be monitored closely. RhIg's mechanism of action is actually suppression of D antigen-specific B cells by the pre-formed antibody:Ag complexes. It sends a signal to those B cells that there is already an immune response to that antigen underway and that it shouldn't become active.

 

[THP]

Mom has baby No. 1.
Mom is Rh-, baby is Rh+.
During gestation, mom develops Rh+ antibodies. Rhogam not indicated for first pregnancy.
Baby No. 1 is delivered no complications and no hemolytic disease.

Baby No.2 comes along, is also Rh+.
Mom is immunized with Rhogam to suppress creation of anti-rhD antibodies which will attack fetus.
Baby is delivered. Success, no hemolytic disease!

Subsequent pregnancies consider rhogam.

This is completely wrong.

 

[THP]

Can someone explain Alloimmunization? Are all Rh negative mothers given Rhogam at 28 weeks? Then, if they baby is Rh + they are given Rhogam again?

Does that mean any mother that has taken Rhogam will test + for antibodies?

The answer to your question is yes. We give give Rhogam at 28 weeks for a reason. The antibodies typically persist in the blood for 12 weeks. 12 weeks after 28 weeks you are at 40 weeks - or your due date. That covers anything that might happen during that time period (ie the patient has a precipitous delivery at home).

If you check an antibody screen after 28 weeks it will typically come back positive, and if you give Rhogam post-partum expect the antibody screen to be positive for about 12 weeks. Eventually the antibody will be cleared from the blood stream so that if you checked an antibody screen, say, 2 years later it will likely be negative (assuming the patient was never isoimmunized).

You can usually distinguish Rhogam from maternal isoimmunization by the titre. If the titre is greater than 1:4 that is almost always due to isoimmunization. The way the lab at my hospital reports the antibody screen is that if its positive and at any point in the pregnancy the patient got rhogam they state it is anti-D due to rhogam. If you are unsure, make you have them run a titre because the lab people don't always check the date of administration and they might say it is due to rhogam when really its due to isoimmunization.