The following are our criteria for performing a KBT:
Order a KBT on an Rh-negative obstetrical patient for any of the following:
post-delivery Fetal Screen test is positive,
trauma during pregnancy (ordered by the physician),
mother had a vaginal bleed, fetal death, terminated pregnancy, amniocentesis or CVS at > 20 weeks gestation,
mother had a version procedure, and/or
neonate is Rh-negative with a positive or invalid Weak D test, or Rh cannot be determined.
At less than 20 weeks we issue one dose of RhIg without further testing, other than the type and screen.
CarrieM has nicely summarized the use of the Immucor FMH RapidScreen if that is the kit you are using.
Additionally at delivery, we use an on-line calculator recommended by the AABB to determine the amount of RhIg to be given based on the mothers height/weight:
W:\AB\Bloodbank2\CAP AABB RhIG calculation\RHIGCALe.zip\