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Test ID FMB Fetomaternal Bleed, Flow Cytometry, Blood

Reporting Name

Fetomaternal Bleed,Flow Cytometry,B

Useful For

Determining the volume of fetal-to-maternal hemorrhage for the purposes of recommending an increased dose of the Rh immune globulin

Specimen Type

Whole Blood EDTA

Ordering 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

Reference Values

≤1.5 mL of fetal red blood cells in normal adults

Day(s) Performed

Monday through Sunday

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

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.


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.

Clinical Reference

1. Roback J, Combs MR, Grossman B, Hillyer C, eds: In: Technical manual. 16th ed. AABB Press; 2008:625-637, 888

2. Iyer R, Mcelhinney B, Heasley N, et al: False positive Kleihauer tests and unnecessary administration of anti-D immunoglobulin. Clin Lab Haematol. 2003;25:405-408

3. Cohn CS, Delaney M, Johnson ST, Katz LM, eds: Technical Manual. 20th ed. AABB Press; 2020

Report Available

Same day/1 day

Method Name

Flow Cytometry