Hemolytic disease of the fetus and newborn in the sensitizing pregnancy where anti-D was incorrectly identified as RhIG.

Hemolytic disease of the fetus and newborn (HDFN) is a potentially fatal complication in Rh-incompatible pregnancies and rarely occurs in the sensitizing pregnancy. Distinguishing RhIG from true anti-D identified is challenging. A case of severe HDFN in which a sample drawn at 28 weeks showed anti-D antibody (3+ strength) attributed to RhIG is described. RBC antibody testing early in pregnancy was negative. At birth, the infant was severely anemic and maternal anti-D titer was 1:256. This case represents a clinically significant anti-D in the sensitizing pregnancy that was missed due to confusion with RhIG. To determine if agglutination strength could be helpful, a retrospective chart-review using both electronic and paper medical records was performed on 348 samples identified as RhIG and 52 true anti-D samples. The agglutination strength of antibody was recorded for each sample. For RhIG, there was an even distribution between the weak to moderate agglutination strength (w+, 1+, and 2+) results (35%, 26%, and 33%, respectively) and just 6% had a 3+ strength. Agglutination strength in patients with high titer (≥1:16) anti-D showed they often (44.4%) have 1+ or 2+ agglutination reactivity. These results show that agglutination strength alone does not provide reliable evidence to distinguish RhIG from high titer anti-D antibodies. We recommend that in cases where there is any uncertainty about whether the anti-D reactivity is due to RhIG, titers should be performed to rule out clinically significant anti-D antibody. © 2022 The Authors. Journal of Clinical Laboratory Analysis published by Wiley Periodicals LLC.

Citation

Mackenzie L Walhof, Judith Leon, Andrea L Greiner, James R Scott, Charles Michael Knudson. Hemolytic disease of the fetus and newborn in the sensitizing pregnancy where anti-D was incorrectly identified as RhIG. Journal of clinical laboratory analysis. 2022 Apr;36(4):e24323

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PMID: 35243688

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