The Rosette Test / Screen for fetal-maternal bleeds
After the baby is born, we take their cord blood (which is thick and gross, by the way) and do a forward ABORh on them. If they are D positive or weak D positive and the mother is negative, the hospital will do an onsite rosette test:
A 3% cell suspension of the mother’s blood is incubated with chemically modified anti-D which will bind to any infant cells. Unbound antibody is washed away and indicator cells (O positive cells treated with ficin to increase reactivity) will bind with infant cells to make little microscopic rosettes/clumps which you can look for with an inverted mic:
All eligible mothers will receive another shot of WinRho regardless of the result because the clumps can be hard to see. However, positive screens indicate a fetal bleed over 30mL (which occurs in about 0.3% of pregnancies), in which case, the mother might need a larger dose, determined by a Kleihauer-Betke (in tomorrow’s post). The WinRho is administered within 72hours because once mom’s discharged, it’s really hard to hunt a lady who just gave birth down just to give her another needle!