Dats Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Dats and links to relevant pages within the course.
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Before beginning the course take some time to review and think about what you already know about HDFN. For example, jot down brief notes to answer the following questions: Which antibody causes the most severe HDFN? Antibodies in which blood group system are the most common cause of positive direct antiglobulin tests (DATs) in newborns but rarely cause clinically significant hemolysis? Should DATs be performed on all newborns regardless of maternal ABO and Rh blood groups? What is Rh immune globulin (RhIg), its source, constituents, purpose, and mechanism of action? Which tests are used to determine postnatal RhIg dosage? Which type of D variant can produce anti-D? What follow-up tests are typically indicated if a pregnant female has a positive antibody screen when initially tested? Which laboratory findings would suggest that an infant may have ABO HDFN? How can the clinical status of fetuses at risk for HDFN be monitored? What are the characteristics of red cells suitable for intravenous transfusion to fetuses suffering from severe HDFN due to anti-D?
|Newborn Serologic Testing Protocols|
Protocols for testing newborns vary internationally and within countries. The table below summarizes some of the more common protocols. Scenario Typical Newborn Testing Protocol Comments Mother is D-negative with no unexpected antibodies Newborn is tested at delivery for: ABO and Rh Test for weak D (mandatory) if initial Rh typing appears to be D-negative Direct antiglobulin test (DAT)* A positive DAT does not always mean that the newborn has clinically significant hemolysis. A positive DAT commonly occurs due to ABO incompatibility, yet infants seldom require treatment. Infants born to mothers who received antenatal RhIg sometimes have a positive DAT that does not cause clinically relevant hemolysis. Mother is Rh positive and a blood group other than group O Routine testing not performed Cord blood retained for a specified period of time (e.g., seven days) in the event that the mother has an unexpected antibody at delivery or the newborn develops signs of red cell hemolysis. Routine testing would result in many positive DATs due to ABO incompatibility- not clinically significant. Mother is group O Rh positive Newborn is tested- especially important if women and their infants are discharged within 24 hours since hyperbilirubinemia due to ABO HDFN may develop later. Optional only if there is appropriate surveillance and risk assessment before discharge and provided there is follow-up (American Academy of Pediatrics). *Policies for DAT testing of newborns whose mothers have received antenatal RhIg vary internationally. For example, the British Committee for Standards in Haematology guidelines state that a DAT should not be performed on cord blood routinely since in some cases it may be positive due to antenatal RhIg prophylaxis. A DAT is recommended only if HDFN is suspected because of a low cord blood hemoglobin or the presence of unexpected maternal antibodies. However in North America, DATs are always performed on infants born to Rh negative mothers who are RhIg candidates.
|Use in Pregnancy|
As applied to pregnancy, RhIg's purpose is to prevent immunization to the D antigen in the perinatal period and thus prevent HDFN due to anti-D. If the mother has already produced anti-D, RhIg is of no use in moderating the immune response.Accordingly, RhIg is routinely administered to Rh negative women not previously sensitized to the D antigen under the following circumstances:1, Antenatal. Antepartum prophylaxis of 300 µg (1500 IU) at about 28 weeks gestation in the USA and Canada, which could be weeks later, depending on how appointments are scheduled. To illustrate variation in antenatal international practice, in the UK, smaller doses of RhIg (e.g., 500 IU) may be given at 28 weeks and 34 weeks, although many UK facilities issue a 1500 IU dose at 28–30 weeks. With antenatal administration, the Rh of the fetus is usually unknown. Some transfusion services recommend a further antenatal dose if the infant is undelivered after 40 weeks.2. Postnatal. Prophylaxis of 300 µg (1500 IU) at delivery of an Rh positive or weak D infant within 72 hours of delivery whenever possible. If RhIg administration is delayed beyond 72 hours, laboratory policies differ as to when it would no longer be administered. The longer the delay, the more likely RhIg may fail to suppress production of anti-D, but it is still worth trying. Note: Because RhIg contains IgG anti-D, when given antenatally, it can cross the placenta and sensitize fetal D-positive red cells. Occasionally the fetus may be born with a weakly positive DAT, but significant hemolysis does not occur. For this reason some guidelines recommend that labs do NOT routinely perform DATs on infants whose mothers have received antenatal RhIg.
|The positive DAT on the newborn means that the infant probably has clinically significant hemolysis.||View Page|
|Routine Serologic Tests - Newborn Protocols|
Protocols for testing newborns vary internationally and within countries.if the mother is D-negative and has no unexpected antibodies, newborns are always tested at delivery.Many labs do not test all newborns if the mother is Rh positive and especially do not test if the mother is a blood group other than group O. If all infants born to Rh positive women were tested, many positive DATs due to ABO incompatibility would be detected that are of no clinical significance. Instead cord blood is retained for a period (e.g., 7 days) should it be needed, for example, if the mother has an unexpected antibody at delivery or if the newborn develops signs of red cell hemolysis.However, some clinical practice guidelines, such as those of the American Academy of Pediatrics specify that testing infants born to group O Rh positive mothers is optional only if there is appropriate surveillance and risk assessment before discharge and provided there is follow-up. (See Further Reading) Not testing becomes an issue if group O women and their infants are discharged within 24 hours as occurs in some locations, since hyperbilirubinemia due to ABO HDFN may develop later. Therefore, some facilities where early discharge occurs require that all infants born to group O Rh positive mothers be tested.Typical protocols: Infants born to Rh negative mothers are tested; Infants born to Rh positive mothers who are group O are often tested, especially if early discharge is common (limiting surveillance); Infants born to Rh positive mothers who are not group O are often not tested and this is acceptable good practice. Cord blood is typically retained for a period should it be needed for testing later.
|Routine Serologic Tests - Newborn|
Tests on Newborn ( mandatory if mother is Rh negative) ABO and Rh*; Mandatory: Test for weak D if initial Rh typing appears to be D-negative; DAT**. * ABO typing of the infant does not require a reverse serum group with A1 and B cells since the newborn is not expected to have ant-A or anti-B (unless of maternal origin).* If cord blood is used for ABO and Rh(D) typing, the red cells should be well washed to remove possible Wharton's jelly.** A positive DAT does not indicate that the newborn has clinically significant hemolysis. For example, a positive DAT commonly occurs due to ABO incompatibility, yet infants seldom require treatment. Also, infants born to mothers who received antenatal RhIg sometimes have a positive DAT that does not cause clinically relevant hemolysis.Also note that policies for DAT testing of newborns whose mothers have received antenatal RhIg vary internationally. For example, the British Committee for Standards in Haematology guidelines state that a DAT should not be performed on cord blood routinely since in some cases it may be positive due to antenatal RhIg prophylaxis. A DAT is recommended only if HDFN is suspected because of a low cord blood hemoglobin or the presence of unexpected maternal antibodies.However in North America, DATs are always performed on infants born to Rh negative mothers who are RhIg candidates.
|A group A Rh positive mother is about to deliver her infant. Is it acceptable good practice not to test the newborn (ABO, Rh, DAT)?Answer Y (for yes) and N (for no)||View Page|