Reduced deformability of circulating erythrocytes: A marker of hyposplenism
Authors: Virginie Prendki, Alioune Ndour, Xavier Jais, Liliane Ciceron, Catherine Settegrana, Pierre Buffet
Journal: American Journal of Hematology (2012)

Reduced deformability of circulating erythrocytes: A marker of hyposplenism To the editor: We read with great interest the article by Lammers et al. [1] reporting on the clinical value of several markers of altered splenic function (hyposplenism). We also recently performed a study to identify relevant markers of hyposplenism. As the spleen mechanically retains altered red blood cells (RBC) [2], blood samples from hyposplenic patients are expected to contain an excess of poorly deformable RBC. We thus used two techniques in our study: rotational ektacytometry (LORCA) and microsphiltration. The former quantifies RBC elongation under shear stress [3], and the latter determines the proportion of RBC unable to squeeze through narrow slits [4]. We compared samples from splenectomized patients to those of nonsplenectomized controls. Mean age (55 vs. 56 years-old), hemoglobin level (13.4 vs. 14.2 g/dL), mean red cell volume (92 vs. 92 fL), mean corpuscular hemoglobin concentration (32 vs. 32 g/dL), and reticulocyte counts (63.24 vs. 62.09 G/L) were similar in both groups. Splenectomy was performed at least 3 months prior to the analysis (mean delay: 9 years) for patients with immune thrombocytopenic purpura (number: 11), abdominal trauma (9), lymphoma or cancer (8), or miscellaneous conditions (7). Patients with recent transfusion, an underlying RBC disorder (as assessed by hemoglobin electrophoresis) or elevated markers of hemolysis were excluded from the analysis. Because splenectomized patients may have splenosis and residual splenic function, only patients with hyposplenism confirmed by the presence of Howell-Jolly bodies on the peripheral blood smear (mean proportion 0.53%, range 0.1–1.51%) were selected for the analysis. In our study, the proportions of pitted cells in 10 hyposplenic patients and 10 controls were respectively 15.84% (range 5.4–23.8%) and 0%, findings consistent with those of Lammers et al. As assessed by the LORCA instrument, the mean elongation index of circulating RBC in 35 hyposplenic patients was significantly lower than that determined in 45 controls (0.614 vs. 0.636, P < 0.001, Fig. 1). When an elongation index of 0.627 at 30 Pascals was used as a cutoff, hyposplenic patients were identified with 89.5% sensitivity and 95% specificity (Fig. 1). No spleen-intact patients had an elongation index lower than 0.624. The mean retention rate of RBC as determined by microsphiltration in a subgroup of 18 hyposplenic patients was 9.6% vs. 1.08% in 18 controls, strongly suggesting that hyposplenic patients have on average a greater proportion of poorly deformable RBC than subjects with normal splenic function. Taken together, these observations strengthen the assumption that subtle but measurable mechanical alterations induce the retention of senescent RBC in the spleen [5]. Measuring the elongation index of circulating RBC is physiologically relevant, requires only small volumes of blood, and provides reproducible, operator-independent results [2]. We agree with Lammers et al. that large studies spanning the wide range of diseases associated with impaired splenic function [6] are warranted. These studies should be focused on selecting the most accurate markers of hyposplenism, determining valid cutoff values to help predict the risk of overwhelming infections with capsulated bacteria or intraerythrocytic protozoans, and identifying preventive measures that are pertinent while eliminating those that are not. Elongation index (El) of the population of circulating red blood cells measured using the Lorca at a shear stress of 30 Pascals in 35 splenectomized patients (S) and in 45 controls (C). Dotted lines indicate important cut-off values (see text). *p < 0.001 (t test) The authors thank Dr Nadia Belmatoug, Dr Damien Carmona, Dr Pierre Chauvin, Pr Olivier Fain, Dr Arsène Mékinian, Pr Marc Michel, Dr Makoto Miyara, Dr Jérôme Stirnemann, Dr Christophe Tresallet. Author Contribution: VP performed the study and wrote the paper; AN, XJ, LC, and CS contributed essential data; PB designed the study and wrote the paper. Virginie Prendki* , Papa Alioune Ndour , Xavier Jais , Liliane Ciceron , Catherine Settegrana§, Pierre Buffet , * Service de médecine interne, Hôpital Croix Saint Simon, Paris, UMR 945, service de parasitologie-mycologie, Hôpital Pitié-Salpêtrière, APHP, Paris, Service de pneumologie, Hôpital Bicêtre, APHP, Le Kremlin-Bicêtre, § Service d'hématologie biologique, Hôpital Pitié-Salpêtrière, APHP, Paris.