Can someone explain the Kleihauer-Betke test in pregnancy like I’m five? I keep seeing it tied to Rh-negative moms and trauma, but I’m fuzzy on when it’s actually used and what the results change in real life.
- When do you actually order KB in pregnancy: any vaginal bleeding, only after bigger bleeds/trauma, after procedures (CVS/amnio/ECV), or just postpartum?
- How does KB compare to the rosette test and flow cytometry-when would one be preferred over the others?
- Does timing matter? If there’s a suspected fetomaternal hemorrhage, how soon should blood be drawn for KB, and do results change if the sample is taken many hours later?
- Can KB say anything clinically useful beyond RhIG dosing-like predicting risk of preterm labor after trauma or correlating with placental abruption severity?
- For twins or higher-order multiples, how do people handle interpreting KB and deciding RhIG dosing, especially if the twins might have different Rh types?
- What are the common pitfalls/false positives? For example, could maternal conditions with higher HbF (HPFH, thalassemia, sickle cell, hydroxyurea use) throw off the KB count?
- What about recent transfusions-do donor RBCs mess with results?
- If the baby is ultimately Rh-negative, is KB still helpful after a trauma/bleed during pregnancy, or is it only relevant if the fetus is Rh-positive?
- In places where KB takes a while to come back, is it standard to give a “default” RhIG dose first and then top up based on KB later?
- Any tips on how clinicians explain KB results to patients (in normal language), especially when the number is borderline?
Would love to hear how different clinics handle this in practice and any gotchas to watch for.