Antibody screening in pregnancy
1% of pregnant women have clinically significant antibodies
12 weeks (10-16) § ABO & D type and antibody screening (by IAT – enzyme technique not necessary) § C, c, D, E, e, K, k, Fya, Fyb, Jka, Jkb, S, s, M, N, Lea § D positive and screen negative § Retest at 28 week § Still negative § No further action § D negative and antibody screen negative § Sensitising events § Prophylactic anti-D § Retest at 28 weeks § Still negative § Routine prophylactic anti-D at 28 weeks § Routine prophylactic anti-D at 34 weeks § Birth, test fetal sample § Baby D-positive ¨ Anti-D ¨ Quantify FMH § D negative and screen positive § Anti-D as above § Past history of IUT, severe HDN, refer to FMU before 20 weeks § Identify antibody § Anti-D or anti-c ¨ Quantify ¨ Test partner ¨ Test at 4 weekly intervals until 28 weeks ¨ 28 weeks – repeat antibody screen Ø test at 2 weekly intervals Ø Prophylactic anti-D now and at 34 weeks if no immune anti-D ¨ Birth Ø Cord sampling for DAT and D type § Anti-K ¨ Quantify ¨ Test partner Ø Partner K negative Ø Retest at 28 weeks and follow normal pathway Ø Partner K positive § Test at 4 weekly intervals until 28 weeks Ø 28 weeks – repeat antibody screen § Test at 2 weekly intervals § Prophylactic anti-D now and at 34 weeks if no immune anti-D Ø Birth § Cord sampling for DAT and D typing § Other clinincally significant antibodies ¨ Repeat screen at 28weeks ¨ If increasing or >32 Ø Refer FMU, Doppler, repeat at 34 weeks, consider early delivery ¨ Birth Ø DAT and D-typing § D positive and screen positive § As above but without anti-D prophylaxis
D-typing § For maternal/ foetal samples use reagents which do not detect Dvariant § All pregnant women found to be D negative should be issued with blood group cards
Antibody screening § Testing for levels of anti-A and anti-B not recommended as their presence doesn’t predict ABO HDN § Test everyone at 28 and 34 weeks § No evidence that antibodies detected only in 3rd trimester cause HDN
Antibodies and HDN § Anti-D § Determine whether immune or prophylactic (likely to be <1) § Anti D prophylaxis should be continued until confirmation that immune § <4iu/mL – HDN unlikely § 4-15iu/mL – moderate risk § >15iu/mL – high risk of hydrops § >4, increasing or history of HDN, refer to FMU § If father herterozygous can D type the baby from a maternal blood sample >16 weeks § Apparent anti-C and anti-D, may actually be anti-G and therefore will need routine anti-D prophylaxis § Assess fetal anaemia with MCA doppler – increased flow = low Hb § Anti-c § <7.5iu/mL – continue to monitor § 7.5-20iu/mL – moderate risk, refer FMU § >20iu/mL – severe risk, refer to FMU § Anti-K § Low HB § Inhibition of early erythroid progenitor cells or promotion of their immune destruction § Severity not correlated with titre § Incidence can be reduced by selecting K negative units for females of child bearing potential (<60years) § K type the father § Others associated with HDN § Anti-C § Anti-E § Anti-Fya § Anti-Jka § Consider early delivery
DAT at birth § Only indicated if mum had red cell antibodies § May be false positive from prophylactic anti-D and Wharton’s jelly § Can be positive by IAT for 8 weeks or more following anti-D § If positive - Check Hb and bilirubin
Anti-D § 500iu IM = treats 4ml FMH (ie. 125iu/ ml IM– 100iu/ml IV) § Large or multiple doses needed, consider limiting batch exposure § Informed consent § Deltoid muscle (Gluteal but absorption will be delayed if only reaches subcut tissue) § Audit trail to allow traceability § Informed consent
Sensitising events (Rh D neg) (PETITE APH) § Pre-eclampsia § Ectopic pregnancy § Termination / Miscarriage / Intrauterine death § Interventions § Amniocentesis / Cordocentesis § Chorionic villous sampling § In-utero therapeutic interventions § Trauma / fall § External cephalic version § APH
§ If pregnancy non-viable and no sample can be obtained from baby, prophylactic anti-D should be administered if mum is D negative § Following sensitising events, anti-D should be administered ASAP and within 72 hours § May be some protection up to 10 days § Passive anti-D is usually <1iu/ml
Assessment of FMH § Sensitising event after 20 weeks § After delivery of a D-positive baby § Kleihauer § Flow using original sample if > 2mls § Number of fetal rbcs/ number of maternal rbcs x 2400 = mls of bleed § Maternal blood volume = 1800mL x 1.22 (fetal cells larger)/0.92 (only 92% stain darkly) = 2400 § 500iu is adequate for up to 4 mls, then calculate on 125iu/ 1ml IM or 100iu/ ml IV § Follow-up maternal sample at 72 hours (48 hours if given iv) after anti-D administration for an FMH of >4mls § More anti-D may be necessary if fetal red cells not cleared. If fetal cells cleared, test maternal serum for presence of anti-D, if no free anti-D, administer further routine dose.
Routine Prophylaxis § D-negative non-sensitised women § DVI – may develop anti D and should be considered D negative as compared to weak D which is considered D positive § 28 and 34 weeks § 500iu
§ Single dose of 1500iu IM at 28 weeks may be adequate
§ Routine doses should not be affected by previous doses for a sensitising event
Trasnfusion testing § Antibody screens may detect circulating passive anti-D § May need to use a panel of D-negative cells to look for other antibodies
§ Anti-D may be passive or immune § If there is doubt, send sample for anti-D quantitation § Passive anti-D rarely exceeds 1iu/mL
§ If anti-D administered within 8 weeks and level <1, test further sample at 28 weeks and continue prophylaxis § If no record of anti-D administration, test at 4 weekly intervals until 28 weeks and then every 2 weeks § If rising it is probably immune § Continue prophylaxis unless immune nature is confirmed
Transfusion of D positive platelets § D negative platelets should be transfused to D-negative women of child bearing potential § If D-pos have to be given, 250iu anti-D will cover up to 5 adult doses
Transfusion of D-positive blood § <15mls transfused – appropriate dose of anti-D § >15mls § Consider using the 2500iu IM injection § If > 2 units § Consider red cell exchange § Single volume – 65-70% reduction § Double volume – 85-90% reduction § Assess residual volume of D-pos cells and calculate anti-D dose (iv) § Follow-up flow every 48 hours until no detectable D-pos cells § Passive anti-D may be detectable for up to 6 months, and tests for immune anti-D may not be positive for several months
ABO HDN § Exceedingly rare in caucasians, higher in Asians, blacks § Stronger expression of A,B antigens § O mum and Aor B baby § DAT may be negative because of low antigen expression on fetal red cell |
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