All about Rh antibodies

Point 1: Can we assess the degree of FMH and thereby avoid titre estimation say in case of APH/Midtrimester abortion? How best to assess the quantum of foetomatrnal haemorrhage (after any insult say ext version, abortion, amniocentesis, APH in  particular , and even iufd and therefore order for titre estimation? ?  Ans: Flow cytometry the method.  The quantum of FHH was used earlier on Kleihauer-Betke test -acid elution technology.  Of late Flow cytometry can offers a unique method of assessing & quantifying FMH. And therefore guiding us about rescheduling the dose of passive antibody (quantum of Rh immunoglobulin) .

Point 2 : What exactly is the clinical relevance of antibody estimating- “TITRE” in the era of “PSV-MCA” (Doppler of Middle cerebral arteries)?  Can PSV-MCA replace the age old method of  “titre estimation” –to which so many uncertainties exist in pertaining to standardization & preservation of sera for onward comparison. Ans:-No. One can’t put one Pt . to Doppler each time . The cost  is also a factor but if Doppler is done  after 28 weeks we can have many more informations regarding foetal wellbeing :-At Kolkata Titre estimation amounts to Rs. 700/- to Rs. 1000/- but Doppler of foetal vessels (after 28 weeks) costs about 2000/- to Rs 2500/- .

 Point 3. What is the critical level of titre (Indirect Coombs test )  after which we have to embark on Serial Doppler to note the degree of foetal anemia induced by foetal haemolysis. What is the relevance of titre estimation in already immunized women?  Ans:-If initial report is above the critical level (most Indian Lab levels is at 1:16, whereas most foreign Lab report as 1: 4 :-then we should proceed for   MCA Doppler for further clinical judgment & action.

Point 4. Any rle of amniocenyersis in modern Obstet ? Ans: Gone are the days of Amniocentesis- & Serial Charting by Liley’s graph:-estimation of foetal affection by  ASS(amniotic fluid spectrophotomerty):- Role of Amniocentesis  in modern obstetric practice ? :-There is still a definite role of amniocentesis if sudden exponential rise of titre occurs especially between 32-34 weeks. If sudden rise of titre then LA is assayed for lung maturity and Bilirubin levelà preg should be continued if immaturity of lungs is documented and Bilirubin level in liquor is < 0.5 mg /dl.

Point 5. If one does titre at all : How to interprete ab titre: - A) It is said that if anti-D titre is less than 4 IU /ml then it is unlikely that she will need active intervention-i.e. foetus is unlikely to get affected in couple of weeks unless there is fresh bout of foeto-mat haeamaorhage. B) It is also said that there is a moderate risk of foetus in utero if titre rages from 4---15 iu/ml. This is sometimes referred as CRTICAL LEVEL of ab (raised titre)-where IUFD can occur or neonate can die due to HDN.It is not the titre but what clinically matters is not the level but speed with which it rises:-However it  has been stressed that it is the trend of rise of ab is more relevant than exact titre level (antibody quantification). It is also been said that the correlation between “titre and degree of foetal anemia” is lost in second preg onwards. However, many consider that the “critical titre for anti-D antibody”in a first affected pregnancy is 1:32(Source:-Moise KJ. Red blood cell alloimmunisation in pregnancy. semin haematol 2005; 169-78.)