Davis's Lab & Diagnostic Tests
Fetomaternal Bleed Determination
General
Synonym/Acronym:
Fetal hemoglobin testing, hemoglobin F, acid elution slide test.
Rationale
To assist in assessing occurrence and extent of fetomaternal hemorrhage (FMH) and calculate the amount of Rh immune globulin to be administered.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
(Method: Flow cytometry) Normal pregnancy: none to a few fetal cells may be present. Laboratory values and reporting units vary by method and each laboratory should be consulted for interpretation of results, especially for assistance in administering the indicated dosage of Rh(D) immune globulin RhoGAM intramuscular (IM) or Rhophylac IM or IV. Note: there are multiple flow cytometry methods differentiated by the antibody used in the assay (e.g., anti-HbF or anti-D).
| Qualitative Screen | Normal Findings | ||||||||||||||||||||||||||||||||||||||||
| Rosette Screen | Negative (A positive finding should be followed up with quantitation by flow cytometry or Kleihauer-Betke to confirm determination of a significant FMH and to determine Rh immune globulin [RhIG] dosage.) | ||||||||||||||||||||||||||||||||||||||||
| Quantitative Methods | Percentage of Fetal Cells | ||||||||||||||||||||||||||||||||||||||||
| Flow Cytometry (e.g., based on counting 50,000 or more cells) | Examples of reportable ranges: 0%–0.03% fetal cells or 1.5 mL of fetal blood; 0%–0.06% fetal cells or 3 mL of fetal blood | ||||||||||||||||||||||||||||||||||||||||
| Kleihauer-Betke (e.g., based on counting a total of 2,000 cells) | 0%–0.1% fetal cells or 5 mL of fetal blood | ||||||||||||||||||||||||||||||||||||||||
| The generally accepted cutoff for a positive fetomaternal bleed determination by flow cytometry or Kleihaur-Betke is 0.1% fetal cells or 5 mL of fetal blood. | |||||||||||||||||||||||||||||||||||||||||
Critical Findings and Potential Interventions
A significant indication of FMH would correspond to:
- Greater than or equal to 0.6% fetal RBCs (or)
- 15 mL of fetal RBCs (or)
- 30 mL of fetal whole blood (assuming fetal Hct is 50%; fetal cells are larger than maternal cells)
The HCP will determine if RhIG should be administered prophylactically or within 72 hr of any potential sensitization (e.g., positive pregnancy test in conjunction with maternal Rh negative blood findings, if indicated at 28 weeks of pregnancy [e.g., Rh negative mother], post-abortion, bleeding after amniocentesis, ectopic pregnancy, falls or other physical trauma during pregnancy, miscarriage, complicated delivery for Rh negative mother).
- If the mother is Rh negative and father is Rh negative, RhIG is not necessary.
- If the mother is Rh negative and the father’s identity/Rh status is unknown or the baby’s Rh status is unknown, RhIG will be administered as a precaution for the current and future pregnancies.
For additional information regarding Rh incompatibility, refer to the studies titled “Blood Typing, Antibody Screen, and Crossmatch Core Lab Study” and “Coombs Antiglobulin, Indirect.”
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