A biparametric flow cytometry analysis for the study of reticulocyte patterns of maturation

Blood Group Testing

Red blood cell (RBC) transfusion is one of the most frequently performed clinical procedures and therapies to improve tissue oxygen delivery in hospitalized patients worldwide. Generally, the cross-match is the mandatory test in place to meet the clinical needs of RBC transfusion by examining donor-recipient compatibility with antigens and antibodies of blood groups. Blood groups are usually an individual's combination of antigens on the surface of RBCs, typically of the ABO blood group system and the RH blood group system. Accurate and reliable blood group typing is critical before blood transfusion. Serological testing is the routine method for blood group typing based on hemagglutination reactions with RBC antigens against specific antibodies. Nevertheless, emerging technologies for blood group testing may be alternative and supplemental approaches when serological methods cannot determine blood groups. Moreover, some new technologies, such as the evolving applications of blood group genotyping, can precisely identify variant antigens for clinical significance. Therefore, this review mainly presents a clinical overview and perspective of emerging technologies in blood group testing based on the literature. Collectively, this may highlight the most promising strategies and promote blood group typing development to ensure blood transfusion safety.

Reticulocyte hemoglobin equivalent in a thalassemia-prevalent area

BACKGROUND

Reticulocyte hemoglobin equivalent (Ret-He), a direct measure of the hemoglobin (Hb) in the young red blood cells, has been reported to be useful in the diagnosis of iron deficiency anemia (IDA) but may have some limitations in thalassemia trait. This study evaluated the differences in Ret-He in school-aged children, and assessed the diagnostic value of Ret-He in identifying IDA in a thalassemia-prevalent area.

METHODS

Blood samples underwent complete blood count analysis, including Ret-He, ferritin, serum iron and total iron binding capacity. Blood samples also underwent Hb typing and a molecular study for α-thalassemia. Receiver operating characteristic analysis was performed to determine the predictive capacity of Ret-He in the diagnosis of IDA. ID was defined as serum ferritin <30 ng/mL and/or transferrin saturation (TSAT) <16%; IDA was defined as serum ferritin <12 ng/mL and/or TSAT <16% with low Hb for age. Normal healthy children (normal controls: NC) had normal iron study, without the thalassemia trait.

RESULTS

Ninety-eight children with a mean age of 12.9 ± 0.6 years were included. Ret-He in the thalassemia trait group (26.7 ± 2.4 pg), ID group (29.0 ± 2.9 pg), IDA group (25.4 ± 2.7 pg), ID + thalassemia trait group (26.6 ± 2.8 pg), and the IDA + thalassemia trait group (24.6 ± 2.3 pg) was significantly lower than in the NC group (30.8 ± 1.7 pg; P < 0.001, 0.01, 0.006, 0.002 and <0.001, respectively). Ret-He had an area under the curve of 0.904 in diagnostic ability for IDA, while a cut-off ≤27 pg had a sensitivity of 91.7% and a specificity of 81%.

CONCLUSION

Ret-He was lowest in subjects with IDA + thalassemia trait. A Ret-He cut-off ≤27 pg was suggestive of IDA in the present study.

Stress reticulocytes lose transferrin receptors by an extrinsic process involving spleen and macrophages

As they mature into erythrocytes during normal erythropoiesis, reticulocytes lose surface transferrin receptors before or concurrently with reticulin. Exosome release accounts for most of the loss of transferrin receptors from reticulocytes. During erythropoietic stress, reticulocytes are released early from hematopoietic tissues and have increased reticulin staining and transferrin receptors. Flow cytometry of dually stained erythrocytes of mice recovering from phlebotomy demonstrated delayed loss of reticulin and transferrin receptors during in vitro maturation compared to in vivo maturation, indicating that an in vivo process extrinsic to the reticulocytes facilitates their maturation. Splenectomy or macrophage depletion by liposomal clodronate inhibited in vivo maturation of reticulocytes and increased the numbers of reticulin-negative, transferrin receptor-positive cells during and after recovery from phlebotomy. This reticulin-negative, transferrin receptor-positive population was rarely found in normal mice. Transmission electron microscopy demonstrated that the reticulin-negative, transferrin receptor-positive cells were elongated and discoid erythrocytes, but they had intracellular and surface structures that appeared to be partially degraded organelles. The results indicate that maturation of circulating stress reticulocytes is enhanced by an extrinsic process that occurs in the spleen and involves macrophage activity. Complete loss of reticulin with incomplete loss of surface transferrin receptors in this process produces a reticulin-negative, transferrin receptor-positive erythrocyte population that has potential utility for detecting prior erythropoietic stresses including bleeding, hemolysis and erythropoietin administration, even after recovery has been completed. Am. J. Hematol. 91:875-882, 2016. © 2016 Wiley Periodicals, Inc.

Examination of Reticulocytosis among Chronically Transfused Children with Sickle Cell Anemia

Sickle cell anemia (SCA) is an inherited hemolytic anemia with compensatory reticulocytosis. Recent studies have shown that increased levels of reticulocytosis during infancy are associated with increased hospitalizations for SCA sequelae as well as cerebrovascular pathologies. In this study, absolute reticulocyte counts (ARC) measured prior to transfusion were analysed among a cohort of 29 pediatric SCA patients receiving chronic transfusion therapy (CTT) for primary and secondary stroke prevention. A cross-sectional flow cytometric analysis of the reticulocyte phenotype was also performed. Mean duration of CTT was 3.1 ± 2.6 years. Fifteen subjects with magnetic resonance angiography (MRA) -vasculopathy had significantly higher mean ARC prior to initiating CTT compared to 14 subjects without MRA-vasculopathy (427.6 ± 109.0 K/μl vs. 324.8 ± 109.2 K/μl, p<0.05). No significant differences in hemoglobin or percentage sickle hemoglobin (HbS) were noted between the two groups at baseline. Reticulocyte phenotyping further demonstrated that the percentages of circulating immature [CD36(+), CD71(+)] reticulocytes positively correlated with ARC in both groups. During the first year of CTT, neither group had significant reductions in ARC. Among this group of children with SCA, cerebrovasculopathy on MRA at initiation of CTT was associated with increased reticulocytosis, which was not reduced after 12 months of transfusions.