Using the daily rate of rise in hemoglobin S to manage RBC depletion/exchange treatment in sickle cell disease.

BACKGROUND: Red blood cell exchange is often used prophylactically in patients with sickle cell disease, with the goal to maintain hemoglobin S (HbS) below a target threshold level. We reviewed whether the daily "rate of rise" (RoR) in HbS that occurs between procedures can be used for patient management. For some patients not achieving their HbS goals despite efficient exchanges, the post-procedure hematocrit (Hct) target is increased to potentially suppress HbS production. This case series explores the utility of this approach, other clinical uses of the daily RoR in HbS, and the factors that influence it. STUDY DESIGN AND METHODS: A total of 660 procedures from 24 patients undergoing prophylactic RBC depletion/exchange procedures were included. Laboratory values and clinical parameters were collected and used to calculate the daily RoR in HbS. Factors such as Hct or medications that might influence the RoR in HbS were evaluated. RESULTS: The RoR in HbS varied widely between patients but remained relatively stable within individuals. Surprisingly, this value was not significantly influenced by changes in post-procedure Hct or concurrent hydroxyurea use. A patient's average RoR in HbS effectively predicted the pre-procedure HbS at the following visit (R2 = 0.65). DISCUSSION: The RoR in HbS is a relatively consistent parameter for individual patients that is unaffected by medication use or procedural Hct targets and may be useful in determining intervals between procedures.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.