What is the protocol for a Kleihauer-Betke (Kleihauer-Betke test) test after a fall in an Rh-negative pregnant patient?

Protocol for Kleihauer-Betke Test After a Fall in Rh-Negative Pregnant Patients

A Kleihauer-Betke test should be performed for all Rh-negative pregnant women who experience a fall or abdominal trauma to quantify potential fetomaternal hemorrhage and determine the appropriate dose of Rh immune globulin needed to prevent alloimmunization. 1, 2

Rationale for Testing

• Fetal RhD antigens are well-developed by 6 weeks' gestation, creating potential for maternal sensitization even in early pregnancy 3
• Trauma, especially abdominal trauma, significantly increases the risk of fetomaternal hemorrhage (FMH) 1
• A positive Kleihauer-Betke test accurately predicts the risk of preterm labor after maternal trauma 1

Testing Protocol

1. Obtain maternal blood sample:

   • Collect 2.5 mL of maternal blood in an EDTA tube as soon as possible after the fall/trauma 4
   • Ideally within 72 hours, though administration beyond this period still offers some protection 2

2. Perform Kleihauer-Betke test:

   • This test detects fetal hemoglobin in maternal circulation
   • Results are reported as volume of fetal blood in maternal circulation
   • Alternative: Flow cytometry may be used if available (better specificity but less accessible) 4, 5

3. Interpret results:

   • Positive test: Indicates fetomaternal hemorrhage has occurred
   • Negative test: No evidence of significant fetomaternal hemorrhage

Rh Immune Globulin Dosing Protocol

1. Standard dosing (when FMH ≤15 mL of fetal red blood cells):

   • Administer one full dose (300 mcg) of Rh immune globulin intramuscularly 2

2. Calculated dosing (when FMH >15 mL of fetal red blood cells):

   • Calculate required dose using the formula:
     • Number of doses = Volume of fetal RBCs (mL) ÷ 15 mL 2
   • Round up to the next whole number of doses if calculation results in a fraction 2
   • Example: If 40 mL of fetal RBCs detected, 40 ÷ 15 = 2.67, so administer 3 doses (900 mcg)

3. Route of administration:

   • Always administer intramuscularly, NEVER intravenously 2

Additional Monitoring

• All patients with a positive Kleihauer-Betke test should receive electronic fetal monitoring due to increased risk of preterm labor 1
• With a negative Kleihauer-Betke test, limited monitoring may be appropriate as the risk of preterm labor is significantly lower 1

Important Considerations

• The Kleihauer-Betke test may have false positives in mothers with hereditary elevation of fetal hemoglobin 4
• Flow cytometry may provide more accurate results but is not universally available 5
• Studies show FMH occurs in 52-60% of pregnancies, but most (87-92.5%) involve <10 mL of fetal blood 6
• In rare cases (1.3-2.7%), FMH may exceed 30 mL, requiring multiple doses of Rh immune globulin 6

Timing Considerations

• If the fall/trauma occurs at 13-18 weeks' gestation and Rh immune globulin is administered, another full dose should be given at 26-28 weeks 2
• If delivery occurs within 3 weeks after the last dose, the postpartum dose may be withheld unless there is significant FMH 2

This protocol ensures appropriate assessment and management of potential fetomaternal hemorrhage following trauma in Rh-negative pregnant women, helping prevent Rh alloimmunization and its associated complications.