Kleihauer Betke Assay Interpretation

The Kleihauer Betke test is an acid-elution cytochemical method used to quantitate fetomaternal hemorrhage.  It identifies cells containing hemoglobin F, based upon the fact that they resist acid-elution to a greater extent than do normal cells.  In addition to fetomaternal hemorrhage, it can be used when the persistence of hemoglobin F is suspected such as in hereditary persistence of hemoglobin F, sickle cell anemia, acquired aplastic anemia, thalassemia, and other hemoglobinopathies.

Kleihauer Betke stains are first shift only tests that must be reviewed by pathology before release, however, if waiting will jeopardize patient care, the hematology manager or charge technician can be call to expedite results.

The percentage of fetal cells is delineated from a specially prepared slide containing the maternal blood sample. The laboratory reports a percentage of fetal cells, i.e.:

Fetal cells % = number of fetal cells counted  X 100%.
                                      total number of RBC counted

Normally, there should be an absence of fetal cells in the maternal blood.  The normal range is 0 to 0.1% as reported by the lab.

Calculations for Estimating the Number of Vials of Rhogam Needed:

• One 300 ml vial of RhIG will protect against 30 ml of D-positive fetal blood.
• The conversion factor used to indicate the volume of fetomaternal hemorrhage (as ml’s of whole blood) is: percent fetal red cells observed X 50.
• The calculation for RhIG is as follows:
   % fetal cells X 50/30 = vials of RhIG required

Example:  1.3% fetal cells calculated on Kleihauer Betke stain

1.3 X 50 = 65 ml of fetal blood

65 ml/30 = 2.2 vials of RhIG required

When the number to the right of the decimal point is less than 5, round down    and add one dose.  Example:  If the calculation comes to 2.2, give 3 vials.

When the number to the right of the decimal point is greater than 5, round up    and add one dose.  Example:  If the calculation gives 2.8, give 4 vials