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HelpTest Code FMB Fetomaternal Bleed, Flow Cytometry, Blood
Reporting Name
Fetomaternal Bleed,Flow Cytometry,BUseful For
Determining the volume of fetal-to-maternal hemorrhage for the purposes of recommending an increased dose of the Rh immune globulin
Method Name
Flow Cytometry
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Whole Blood EDTAOrdering Guidance
This test is for the detection of fetal bleed, it should not be used to detect the hereditary persistence of fetal hemoglobin (HPFH) or to detect fetal maternal hemorrhage in a mother with HPFH. For HPFH diagnosis, order HBEL1 / Hemoglobin Electrophoresis Evaluation, Blood.
NY State Clients: testing is available; order FMBNY / Fetomaternal Bleed, New York, Blood.
Shipping Instructions
Specimen must arrive within 5 days (preferably 24-72 hours) of collection.
Specimen Required
Container/Tube: Lavender top (EDTA)
Specimen Volume: Full tube
Collection Instructions:
1. Do not centrifuge.
2. Invert several times to mix blood.
3. Send whole blood specimen in original tube. Do not aliquot as aliquoting into or out of a sample tube can adversely affect test results.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole Blood EDTA | Refrigerated (preferred) | 5 days | |
| Ambient | 5 days |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
| Clotted blood | Reject |
Reference Values
≤1.5 mL of fetal red blood cells in normal adults
Day(s) Performed
Monday through Sunday
CPT Code Information
88184-Flow cytometry, cell surface, cytoplasmic
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| FMB | Fetomaternal Bleed,Flow Cytometry,B | 75308-7 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 28204 | Mother's Rh | 10331-7 |
| 28202 | Fetal-Maternal Bleed | 55730-6 |
| 28203 | Rh Immune Globulin | 55731-4 |
| 4058 | Remarks | 48767-8 |
Clinical Information
In hemolytic disease of the newborn, fetal red blood cells become coated with IgG alloantibody of maternal origin, which is directed against an antigen on the fetal cells that is of paternal origin and is absent on maternal cells. The IgG-coated cells undergo accelerated destruction, both before and after birth. The clinical severity of the disease can vary from intrauterine death to hematological abnormalities detected only if blood from an apparently healthy infant is subject to serologic testing.
Pregnancy causes immunization when fetal red blood cells possessing a paternal antigen foreign to the mother enter the maternal circulation, an event described as fetomaternal hemorrhage (FMH). FMH occurs in up to 75% of pregnancies, usually during the third trimester and immediately after delivery. Delivery is the most common immunizing event, but fetal red blood cells can also enter the mother's circulation after amniocentesis, spontaneous or induced abortion, chorionic villus sampling, cordocentesis, or rupture of an ectopic pregnancy, as well as blunt trauma to the abdomen.(1)
Rh immune globulin (RhIG, anti-D antibody) is given to Rh-negative mothers who are pregnant with a Rh-positive fetus. Anti-D antibody binds to fetal D-positive red blood cells, preventing development of the maternal immune response. RhIG can be given either before or after delivery. The volume of FMH determines the dose of RhIG to be administered.
Interpretation
Greater than 15 mL of fetal red blood cells (RBC) (30 mL of fetal whole blood) is consistent with significant fetomaternal hemorrhage (FMH).
A recommended dose of Rh immune globulin (RhIG) will be reported for all specimens. One 300 mcg dose of RhIG protects against a FMH of 30 mL of D-positive fetal whole blood or 15 mL of D-positive fetal RBC. Recommended standard of practice is to administer RhIG within 72 hours of the fetomaternal bleed for optimal protective effects. The effectiveness of RhIG decreases beyond 72 hours post exposure but may still be clinically warranted. This assay has been validated out to 5 days post collection.
Cautions
Clinical conditions exist that may result in an increased level of fetal hemoglobin-containing red blood cells (RBC), including hereditary persistence of fetal hemoglobin and thalassemia. Such RBC (also referred to as F cells) are detected by this assay. Results must be interpreted with caution in these situations.
Due to differential RBC densities, aliquoting into or out of a sample tube can adversely affect the results.
Method Description
The fetomaternal bleed test identifies cells containing fetal hemoglobin. The cells are fixed and permeabilized and then incubated with monoclonal antibodies directed against fetal hemoglobin (HbF) and subsequently analyzed by flow cytometric methods. This test uses the US Food and Drug Administration-approved Invitrogen Fetal Hemoglobin kit with fluorescein isothiocyanate-conjugated monoclonal antibody directed to HbF (HFH-01).(Package insert: Invitrogen Fetal Hemoglobin Test Kit with FITC-conjugated Monoclonal Antibody Directed to HbF. Life Technologies Corporation; MAN 0003641, Rev 3.02 03/06/2013)
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Rh immune globulin (RhIG) dose calculation: mL of fetal bleed/15 equals the calculated doses of RhIG, then add a safety margin, ie, when the number to the right of the decimal point is less than 5, round down and add 1 dose (example: 2.2 = 2.0 + 1 = 3); when the number to the right of the decimal point is 5 or greater, round up to the next number and add 1 dose (example: 2.8 = 3.0 + 1 = 4). If fetal bleed is 1.5 mL or less, it will be reported as negative bleed and the RhIG dose will be 1.
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RhD-Agglutination of red blood cells with an antiserum represents the presence of the corresponding antigen in the red blood cells.(Cohn CS, Delaney M, Johnson ST, Katz LM, eds: Technical Manual. 20th ed. AABB Press; 2020)