Guidelines for blood grouping and red cell antibody testing during pregnancy

1. Guidelines for blood grouping and red cell antibody testing during pregnancy Transfusion Medicine, BCSH

2. INTRODUCTION • ABO Rh D-typing and antibody screen tests on the sera of the pregnant women are performed for the protection of the mother and the identification of HDN • The guidelines are addressed to the hematology unit undertaking such antenatal testing. • It is accepted that samples should be tested only when it is likely that results could influence the clinical management of the pregnancy.

3. OBJECTIVES • The objectives of routine serological testing are: a) Identify pregnancies at risk of fetal and neonatal HDN b) Identify RhD-negative women who need anti-D Ig prophylaxis c) Provide compatible blood swiftly for obstetric emergencies.

4. OBJECTIVES • 2) When red cell ab are present, the purpose of f/u serological tests are: a) identify the fetus that may need treatment before term b) predict infants who are likely to require treatment for HDN in the neonatal period c) identify any additional red cell allo ab developing during the course of the current pregnancy. d) identify additional maternal ab induced by intrauterine red cell transfusions

5. Testing protocols 1) All pregnant women • The first antenatal examination at booking is usually at 10-16 wks POA- test for ABO and RhD gp and presence of red cell alloab • When an ab screen is +, further testing sh be carried out to determine ab specificity and significance. • Subjects who have weak RhD blood groups are RhD + & do not form immune anti-D

6. Cont: • It is essential that pt with ab of clinical significance sh be referred for advice to a specialist at the earliest oppurtunity • Testing for ABO immune ab in the maternal serum is not recommended as their presence neither predicts ABO HDN nor causes problems in utero

7. Testing Protocols 2) No red cell ab detected at booking • They sh be retested once during 28-36 wks gestation. • Rh D-negative women sh have at least 2 tests performed during this period, one of which sh be at 34-36 wks(optional)

8. Cont: 3) Red cell ab present at booking • If have previous affected baby by HDN, they sh be referred early to a specialist unit for advice before 20 wks gestation for assessment for fetal haemolysis, irrespective of ab level. • This will enable the need for amniocentesis and/ or fetal bl sampling and intrauterine transfusion • Neither the specificity nor the level of maternal rbc ab can precisely predict outcome for the infant.

9. Cont; • When an ab or abs are detected at 10-16 wks of gestation, subsequent testing sh be done to determine the specificity, concentration , origin and level of ab or abs and the likelihood of HDN • Anti-D, anti-c & anti-Kell are abs most often implicated in causing moderate to severe HDN

10. Paternal Sample • When a clinically significant ab capable of causing HDN is present in a maternal sample, testing the partner’s phenotype provides useful information to predict the likelihood of a fetus carrying the relevant rbc ag

11. Women with anti-D • If have anti-D detected, they sh be tested at least until 28 wks and every 2 wks thereafter to monitor the level of anti-D and to identify any additional abs that might develop • When intrauterine transfusion are given, the maternal serum sh be screened for additional abs prior to each transfusion

12. Cont; • Titration of anti-D does not closely correlate with the occurrence of HDN • Anti-D quantification using the national anti-D std is more reproducible and correlates more closely with the likelihood of HDN • An increase of anti-D level by 50% or > over the previous level indicates a significant rate of increase, irrespective of period of gestation

13. Cont: • Anti-D is the rbc alloab most frequently responsible for serious HDN. • Generally the significance of the anti-D level is as follows,although exceptions can occur. • Anti-D < 4iu/ml HDN unlikely • Anti-D 4-15 iu/ml moderate risk of HDN • Anti-D > 15 iu/ml high risk of hydrops fetalis

14. Women with rbc alloab other than anti-D • All non-D abs reacting with indirect antiglobulin test sh be titrated against RBCs heterozygous for the corresponding ag • Anti-c and ab within Kell bld gp system with or without other abs are the non-D abs most likely to cause haemolytic disease severe enough to warrant antenatal intervention • They sh be retested with the same frequency as women with anti-D.

15. Cont; • For all other abs reactive by IAT, retesting once at 28-34 wks provide enough info to determine mx of pregnancy • Significant titres likely to cause HDN are a titre of 32 or > except for Kell-related abs which may affect the fetus regardless of the titre • In general, anti c, -K,-e,-Ce, Fya, Jka and –Cw have greatest potential to cause HDN.

16. Cont; • Anti- Lea, -Leb,-Lua, -P, -N, -Xga and high-titre low-avidity abs eg; Knd have not been implicated in HDN.

17. Action at time of delivery • Maternal samples and a cord blood sample sh be taken at delivery from Rh-negative women with no immune anti-D • The cord bld sample sh be used to determine the infant’s Rh D grp,can identify the women who must receive prophylactic anti-D Ig • When the infant is RhD positive, the DCT sh be done on the cord rbc.

18. Cont; • This is to identify HDN due to anti-D developing in late pregnancy . • A positive DCT has been shown to be a good predictor of HDN • A test should be done on the maternal bld sample to establish the size of the fetomaternal bld so that additional anti-D Ig may be given when required

19. Cont; • DCT sh be done on cord rbc when the maternal serum contains clinically significant rbc abs • if +ve, rbc eluate can identify the rbc ab specificity • Wherever possible, the rbc from the cord sh be tested for the corresponding rbc ag

20. Cont; • All infants born to mothers who have clinically significant abs in their serum sh be closely observed for the evidence of HDN during the next 48-72h of life • They sh not be discharged earlier unless subsequent follow-ups is arranged • the next 48-72h

21. Testing of bld samples fr women who have received a/natal prophylaxis with anti-D Ig • Antenatal prophylaxis with anti-D IgG is practised in some regions. • Passive anti-D may be detectable in the serum by enzyme tests as well as by IAT for up to 12 wks or more after the administration of anti-D IgG. • Testing of maternal serum for anti-D prior to the second prophylactic dose or post-delivery may be confusing and isnot recommended as passive anti-D cannot be differentiated fr alloimmune anti-D

22. Cont; • When non-D abs are present in a woman who received antenatal anti-D IgG prophylaxis, the testing protocol already described for this gp of patients sh be followed