Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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        FetalDex test, baby's cord blood

Kleihauer Betke test, cord blood

This was originally the Kleihauer-Braun-Betke test, introduced in the 1940s. This test is done on a smear of mother's blood. In our institution, it follows (1) a positive FETALSCREENO rosette screening test on mother's blood (FetalDex test was a previous test). Screening positivity suggests presence of a feto-maternal bleed (but there can be false positivity due to a positive direct antiglobulin tests [DAT] or baby cells "weak D" and false negativity (1) if fetomaternal ABO incompatibility & baby's red cells immediately eliminated from mother's blood stream) & (2) if the bleed in the placenta is immediately and totally confined by the intrachorionic thrombus [L07-6983]...and Kleihauer-Betke test stain is used to help quantitate the feto-maternal bleed. The stain gives a red color to a site in fetal hemoglobin (contained in RBCs with hemoglobin F) in baby's red blood cells which have gotten into the mother's circulation (and also stains platelets and some WBCs positively). The mother's non-fetal-hemoglobin cells have become pale by having acid elution of adult hemoglobin from them. A standard  30mL dose of Rhogam is given within 72 hours to every Rh negative mother delivering an Rh positive baby; an additional dose is said to go to any mom whose circulating fetal cells are greater than 0.6%. Testing might be done (2) in any pregnant woman having surgery, amniocentesis, or trauma which might have affected the placenta and released fetal is a search for evidence of injury of the integrity of the placental barrier between fetal & maternal blood (as a surrogate for injury to the fetus) and does not depend on Rh type. (3) It may be done if typing detects a weak D because a fetomaternal bleed of Rh+ baby's blood into Rh- mom would react weak D.

Flow cytometry, an expensive technology, is more universally exacting at detecting Rh+ cells.

Placenta examination: during our pathology exam of the baby's placenta, if ordered by the delivering clinician, we may find one or more "infarct-like" intrachorionic thrombi as we slice the organ. These are thought to reflect fetomaternal hemorrhage.

Normal (<0.1% of RBCs):

  1. normal babies

  2. minimal, inconsequential feto-maternal bleeds or bleeds walled off in the intrachorionic clot or mopped up by maternal RBC antibodies already present against that baby's RBCs,


  1. hereditary persistence of fetal hemoglobin

  2. feto-maternal hemorrhage (FMH) [LMC-01-5295 K-B was3%, died, no placental intrachorionic thrombi]

  3. intrachorionic thrombi discovered on placental exam suggest a FMH with possibilty of maternal RBC sensitization before the next pregnancy.


  1. CAP Today November 2003...see CAP website.

(posted 2002; latest addition 18 August 2007)
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