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[Read eLetter] Fetal-Maternal Hemorrhage Detection in Ontario
John Lafferty, MLT, ART   (2 October 2003)

Fetal-Maternal Hemorrhage Detection in Ontario 2 October 2003
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John Lafferty, MLT, ART
Ontario Medical Association

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Re: Fetal-Maternal Hemorrhage Detection in Ontario

lafferty{at}hhsc.ca John Lafferty, MLT, ART

Hemolytic disease of the newborn (HDN) is the result of maternal antibodies causing destruction of antigen positive erythrocytes in the fetus. The most serious form of HDN is caused by maternal alloantibodies directed against the D antigen of the Rh blood group system. In this scenario Rh-negative mothers are alloimmunized during pregnancy with an Rh-positive fetus. HDN occurs in subsequent pregnancies when maternal anti-D crosses the placenta and destroys Rh-positive fetal cells. The incidence of Rh HDN has been reduced drastically by Rh0(D) immune globulin (RhIg) prophylaxis in Rh-negative women. The effective detection and quantitation of fetal-maternal hemorrhage (FMH) after delivery is essential for ensuring adequate RhIg prophylaxis. The acid elution techniques, e.g., Kleihauer or Nierhaus Betke, are the most commonly used FMH detection and quantitation techniques in Ontario. A number of laboratories in Ontario use the Rosette test to detect FMH followed by subsequent quantitation by acid elution if the Rosette test is positive. Reports in the literature suggest the acid elution techniques are unreliable.[1-3]

The Hematology Committee of the Quality Management Program-Laboratory Services (QMP-LS), a department of the Ontario Medical Association, which carries out external quality assurance (EQA) of medical laboratories, has just published a review of the Ontario FMH detection and quantitation EQA program.[4] This review found that the Rosette and acid elution techniques could reliably identify patients who may require additional RhIg prophylaxis but that the acid elution techniques lack adequate accuracy and precision for the reliable quantitation of an FMH once detected. The review included six surveys where the target FMH could have required additional RhIg prophylaxis, i.e. >10mL FMH. The percent error of the mean from the target FMH was 20% or greater in five of six surveys. Furthermore, the inter-laboratory reproducibility was poor with coefficients of variation ranging from 39.5% to 71.8%. These results had the potential to cause inadequate RhIg prophylaxis in 19.4% (54 of 278) of the survey challenges. The adoption of the American Association of Blood Banks (AABB) recommendation of adding an extra 300ug RhIg dose in addition to the dose required for the volume of FMH detected reduced the potential for inadequate RhIg prophylaxis from 19.4% to 0%.[5] The review concludes that:

a) The Rosette and acid elution techniques are effective screening techniques to identify patients who may require additional RhIg prophylaxis. b) The acid elution techniques lack adequate accuracy and precision for the reliable quantitation of FMH. c) Following the AABB recommendation of adding a 300-ug dose of RhIg to the dose required for the volume of FMH detected is an effective strategy for overcoming the limitations of the acid elution techniques.

In summary, the QMP-LS endorses adherence to the AABB recommendation of adding an extra 300ug RhIg dose - to the dose required for the volume of FMH detected by acid elution techniques.

Sincerely,

John D. Lafferty, MLT, ART

Anne Raby, MLT, ART

Linda Crawford, MT(ASCP)

Lori Anne Linkins, MD, FRCPC

Harold Richardson, MD, FRCPC

Mark Crowther, MD, FRCPC

References

1. Polesky HF, Sebring ES. Evaluation of methods for detection and quantitation of fetal cells and their effect on RhIgG usage. Am J Clin Pathol 1981;76(4 suppl):525-529.

2. Duckett JRA, Constantine G. The Kleihauer technique: an accurate method of quantifying fetomaternal haemorrhage? Br J Obstet Gynaecol 1997;104:845-846.

3. Raafat A, Fraser N, Main F et al. A quality assurance scheme for the Kleihauer test: the Scottish experience 1988-1996. Transfus Med 1997;7:221-226.

4. Lafferty JD, Raby A, Crawford L, Linkins LA, Richardson H, Crowther M. Fetal-maternal hemorrhage detection in Ontario. Am J Clin Path 2003;119:72-77.

5. Perinatal concerns in transfusion practice. In: Vengelen-Tyler V, ed. Technical Manual. 13th ed. Bethesda, MD: American Association of Blood Banks; 1999:505-508.

Conflict of Interest:

None declared