Reticulocyte Hb expression reported by the Mindray BC6800 Plus analyzer for the detection of iron deficiency in patient blood management

Introduction

Background

Patient blood management (PBM) is a patient-centered, multidisciplinary, evidence-based approach that aims to optimize the use of blood products to improve patient outcomes. Anemia and iron deficiency (ID) predispose to an increased risk of transfusion in surgical patients with a consequent increase in morbidity and mortality. Those clinical conditions are modifiable risk factors for poor outcomes identified as a key component of comprehensive PBM (1-3). “Suboptimal” preoperative hemoglobin (Hb), defined as Hb <130 g/L regardless of sex, increases the risk of transfusion in patients undergoing major surgery and is associated with increased morbidity, mortality and length of stay (4,5). The most common cause of anemia globally is ID (6). In patients with scheduled primary hip or knee arthroplasty, it is recommended to perform a complete blood count (CBC) at least 30 days before surgery to optimize Hb before surgery. Serum ferritin level and the transferrin saturation must be analyzed to evaluate iron stores and functional iron (7,8). However, ferritin is an acute-phase reactant, and it can provide unreliable results in the presence of inflammatory and malignant diseases. Transferrin saturation essentially offers a measure of trafficking iron, but its value fluctuates depending on recent dietary iron intake (9). Evaluating the true iron stores and erythropoiesis status is still a challenge since no “gold standard” exists on biomarkers for assessing iron status yet (10).

Rationale

It is not only anemia, but ID can occur without anemia (latent iron deficiency; LID). Recognizing deficiencies in time is crucial as part of PBM. The spectrum of ID is a sequential and long process before Hb drops to the anemia level. Patients awaiting surgery may have optimal Hb and present with an “absolute” ID, iron sequestration (functional ID) and/or insufficient iron stores to compensate for the expected blood loss, and the anemia could develop in the waiting time before surgery (11). Due to their short life span, reticulocytes and derived parameters reflect the current erythropoiesis status before Hb and mature red cell indices decrease and anemia is established. The reticulocyte Hb content has been recommended for studying erythropoiesis status because, irrespective of inflammation, it can correctly evaluate ID during the acute phase response, detecting iron depletion latent and functional ID (12-16).

In the context of the preoperative evaluation of surgical patients, the reticulocyte Hb content can identify suboptimal hemoglobinization in early stages so a negative iron balance can be detected in time to induce changes in nutrition and supplemental medication to prevent the development of anemia and the replenishment of iron stores before surgery (17,18). For these reasons, the “international consensus statement on the management of anemia in major surgical procedures” has been included in the “international consensus statement on the management of anemia” (19).

At this point, it must be stated that reticulocyte Hb content is not of general use. The first hematology counter able to measure and report it was the Bayer Technicon H*1 (20). Later, other manufacturers offered similar parameters in their analyzers (21). Unfortunately, an international standard for reticulocyte Hb content does not exist. Instrument-specific reference ranges, and clinical decision cut-off values must be established, and the information must be evaluated to prove the potential clinical utility in different clinical situations.

Objective

In the context of PBM, most of the literature refers to reticulocyte Hb content measured as RET-He or CHr, proprietary names of the manufacturers Sysmex (Kobe, Japan) and Siemens Healthineers (Erlangen, Germany), respectively, with good correlation and similar clinical meaning (22,23). Less information on the more modern Mindray BC6800 Plus analyzer (Mindray Diagnostics, Shenzhen, China) is available. To expand our knowledge on this counter-specific reticulocyte Hb content, the so-called reticulocyte Hb expression (RHe), we evaluate its diagnostic performance in detecting iron-restricted erythropoiesis in the preoperative evaluation of patients undergoing arthroplasty. We present this article in accordance with the STARD reporting checklist (available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-28/rc).

Methods

Quality control

Quality control assurance was carried out according to the manufacturer’s instructions. The quality of results was validated by routine use of BC-6D and BC-RET quality control materials (Mindray Diagnostics), based on three different levels: mean, standard deviation (SD) and coefficient of variation (CV) were recorded daily for CBC and reticulocytes to establish the between-batch precision. The long-term accuracy of results is controlled with a pilot External Quality Control program held by the Spanish Society of Hematology and Hemotherapy in association with the Spanish Society for Medical Laboratory.

Study design, patients, laboratory parameters

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by our Institutional Ethics Research Committee (OSI Barrualde Comité de Etica en Investigación, reference No. 1055/22) and individual consent for this retrospective analysis was waived.

Over three months in 2022, we recruited adult patients during their preoperative analytical evaluation before arthroplasty at Hospital Galdakao Usansolo. We excluded patients who had received blood transfusions in the preceding month and thalassemia carriers. The diagnostic, clinical data, comorbidities and treatments were retrieved from the laboratory and medical records.

Blood samples were run in the Mindray BC 6800 Plus analyzer within 6 hours of collection. C-reactive protein (CRP), s-iron, transferrin and s-ferritin were assayed in a chemical analyzer Cobas c711 with Tina quant reagents (Roche Diagnostics, Mannheim, Germany).

Anemia and iron status definitions

The World Health Organization (WHO) defines anemia as Hb <130 g/L in adult males and Hb <120 g/L in non-pregnant adult females (24) and LID when the patient is not anemic, with s-ferritin <30 µg/L. Anemia of any other cause than ID was not further specified. We defined absolute ID as s-ferritin <15 µg/L according to WHO; stores can be low, and typically, s-ferritin decreases to 30 µg/L without anemia, the threshold for iron-restricted erythropoiesis. Functional ID due to low availability, typical of anemia of chronic disease (ACD), was defined as a combination of inflammatory conditions (CRP >5.0 mg/L), transferrin saturation <20% and/or s-ferritin <100 µg/L. We consider sub-optimal Hb for patients awaiting surgery with a moderate-high risk of bleeding when Hb <130 g/L for both genders and sub-optimal iron stores for bleeding surgery s-ferritin <100 µg/L (5).

Statistical analysis

Data normality was assessed by the Kolmogorov-Smirnov test. Non-parametric data were described as median and interquartile range (IQR). For computing sample size, standard values for alpha and beta were used 0.05 and 0.20, respectively, which allows for 80% power). Mann-Whitney U test was applied to detect statistical deviations between the patients with normal iron stores and those with ID. P value <0.05 was considered significant. Receiver operating characteristic (ROC) curve analysis was utilized to illustrate the diagnostic performance of RHe in detecting ID using s-ferritin <30 µg/L as a gold standard. Data were analyzed using SPSS statistical software version 29.0 (IBM, USA).

Results

Precision values were a SD <0.5 pg with %CV <2.0% in the three levels of the control materials, lower than the 5% limit specified by the manufacturer. A total of 369 patients were studied (men 45.5%, age range 35–80 years; women 54.6%, age range 46–78 years). A total of 379 patients were initially recruited; 10 of them did not fulfill the inclusion criteria and were excluded. Table 1 summarizes their demographic and clinical data. Figure 1 shows the flow chart of the whole cohort. 7.3% of the patients suffered from anemia according to the WHO criteria, with no significant differences between men (6.9%) and women (7.4%) (P=0.08); 62.5% of them also had some ID (45% pure ID and 17% inflammatory iron profile). The RHe values in iron deficiency anemia (IDA) and ACD had no significant difference (P=0.09), IDA median 26.8 pg (IQR 23.6–27.3 pg), ACD median 27.3 pg (IQR 25.3–29.0 pg).

Figure 1 Patient flow diagram. LID, latent iron deficiency.

In the group of non-anemic patients (n=342), 15.5% showed sub-optimal Hb. The percentage of patients with sub-optimal ferritin levels was 39.8%, nearly three times the suboptimal Hb. Most of them had low iron stores, and only 1.8% presented iron sequestration (functional ID); 31.4% had s-ferritin values below the threshold for iron-restricted erythropoiesis, 30 µg/L; in this group, 81% of them had RHe <30 pg. Median RHe in the LID group was 26.1 pg, statistically different from that in the group with normal iron stores (30.9 pg, P<0.001, Figure 2). Table 2 shows the CBC, biochemistry, Iron parameters and RHe in both groups. RHe performed best, with an area under the curve (AUC) of 0.825 (95% CI: 0.747–0.895). At the cut-off of 30.0 pg, the sensitivity was 82.8%, and the specificity was 70.1%. Table 3 presents the sensitivity and specificity values of the different cut-off values. Hb, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and red cell distribution width (RDW) rendered 0.539, 0.734, 0.728 and 0.774, respectively (Figure 3).

Figure 2 Box & whiskers plot representing reticulocyte Hb expression values of non-anemic patients divided according to their erythropoietic status: normal iron (adequate supply, n=235) or iron deficiency (iron restricted erythropoiesis, n=107). Hb, hemoglobin.

Figure 3 Receiver operating characteristic curve analysis to illustrate the diagnostic performance of RHe in detecting iron deficiency using s-ferritin <30 µg/L as gold standard. RHe, reticulocyte Hb expression; MCH, mean corpuscular hemoglobin; MCV, mean corpuscular volume; RDW, red cell distribution width; Hb, hemoglobin.

Discussion

Key findings

We evaluated the diagnostic performance of RHe detecting iron-restricted erythropoiesis in the preoperative evaluation of patients undergoing arthroplasty, and our result was that Re had the best performance compared to other parameters.

Strengths and limitations

Nevertheless, a limitation of this study is that it was performed at a single center; therefore, a prospective multi-centric study that included more patients would confirm the promising results. The value of RHe in managing the treatments to correct ID was not explored, and our findings suggest that future controlled studies are needed to investigate this potential utility further.

Explanation of findings

From a public health perspective, PBM is a prevention strategy that goes beyond the optimal use of blood products. The essential elements of PBM programs are based on preventing and correcting risk factors that could lead to the need for transfusion and reducing moderate and severe complications. The prevalence of anemia in Western Europe for the general population is estimated to be 6–11.1%, depending on whether men or women with age, and in specific populations such as patients with cancer, kidney failure, inflammatory bowel disease, or heart failure, with an impact on quality of life (25,26). The percentage of anemia found in our cohort was lower than reported when similar patients were evaluated. In contrast, the prevalence of deficiencies was more or less the same percentage (11,27,28).

It should be noted a high percentage of non-anemic patients with adequate Hb levels have suboptimal iron levels. Iron stores will gradually decrease when demand or losses increase or absorption decreases. ID has several stages, starting with iron depletion, which is followed by ID erythropoiesis and, if not detected, ends up causing anemia (typically microcytic and hypochromic) when there is not enough iron available for the synthesis of Hb. ID is a progressive process of depletion of the stores, while the half-life of circulating erythrocytes is around 120 days, so the CBC may be normal at the beginning of ID. As ID progresses, erythrocytes contain less Hb since there is a negative balance between the need for iron in erythropoiesis and the supply, so the red blood cells will be increasingly hypochromic and microcytic. However, due to the long half-life, several cohorts coexist, and only minor changes in the CBC can be detected, as is the case with the alteration of the RDW. Therefore, erythrocyte indices and Hb have a low sensitivity for early ID detection, as their values do not decrease until advanced stages (29,30).

The RDW quantifies the variation in the volume of the erythrocytes. High values indicate anisocytosis. In our study, RDW was the most sensitive parameter of the CBC for detecting LID. Rapid and effective diagnosis and treatment of ID is a key component of PBM; reticulocyte Hb content fits this purpose with an advantage from CBC. Also, changes in the status of erythropoiesis in response to treatment can be recognized earlier based on reticulocyte-derived parameters when only minor changes can be detected in the CBC and, based on these parameters, iron-restricted erythropoiesis cannot be suspected (16).

Comparison with similar research

Reticulocyte Hb content has been a useful marker of ID in several populations, including newborns, children, adolescents, blood donors, the elderly, pregnant women, and patients undergoing dialysis for chronic kidney disease, inflammatory bowel disease, and rheumatologic disorders. It can monitor the response to iron supplementation and PBM (19). The suggested thresholds for predicting ID vary from 25.0 to 30.0 pg (31). The range values of RHe in healthy subjects are 28.9–37.5 pg, median 33.2 pg, and 23.7 pg in microcytic anemia (32). Our cut-off for RHe agrees with the values used in the protocol, optimizing pre and postoperative anemia treatment by detecting ID using RET-He, reported by Sysmex analyzers, 30.6 pg.

This protocol reduces the blood cell transfusions needed for major hip and knee surgeries (33). The value of RET-He was studied and eventually adopted as a routine parameter to screen for anemia and iron status before arthroplasties (34). Both Sysmex and Mindray counters apply fluorescence and light scattering (with sphering cells) despite gating and angles being slightly different, and the e-dyes are Asymmetric cyanine (Mindray Diagnostics) and Polymethine (Sysmex XN-Series). Our results agree with previous reports published based on data from Sysmex analyzers: RHe performs similarly to Ret He in detecting LID. Moreover, the optimal cut-off is the same.

Implications and actions needed

Pre- and postoperative measurement of reticulocyte Hb content as a part of CBC has been suggested to proactively initiate treatment, with the strategic administration of iron in patients in whom reticulocyte Hb content indicated deficient erythropoiesis, to avoid complications, anemia post-surgery and to prevent longer hospitalization (35). Reticulocyte Hb content provides an immediate indication of the current erythropoiesis status, with adequate iron supply or not, so it is a useful parameter for monitoring the efficacy of the treatments because changes in erythropoiesis in response to iron supplements can be detected earlier with values rising within days.

The typical treatment period between identifying ID anemia and the surgery date is usually from two weeks to one month. Identifying early iron sufficiency post-iron therapy is essential when treatment time before surgery is short; when IV iron is the option, reticulocyte Hb can provide valuable information about the patient’s iron status in the early periods post first infusion when other tests are not informative (36).

Conclusions

Modern hematology analyzers can measure diverse parameters, which allow obtaining a fast (with a unique sample and visit) clear picture of the erythropoiesis status of patients and are valuable tools for the management of anemia and ID, guiding the clinicians in their selection of the best and most efficient therapy for every patient. For a rational and successful preoperative anemia diagnosis and therapy, a timely identification/screening of patients is crucial. RHe, measured during a routine reticulocyte analysis, is useful in diagnosing patients at risk for latent and/or functional ID. Measuring RHe as a routine preoperative parameter could thus be a valuable, quite inexpensive option for a strategic adoption of PBM in surgical practice, contributing to reducing costs and improving outcomes of the patients undergoing surgery. For all patients, surgical and medical, displaying ID with or without anemia, this allows an effective iron substitution in the context of PBM.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STARD reporting checklist. Available at https://jlpm.amegroups.com/article/view/10.21037/jlpm-24-28/rc

Data Sharing Statement: Available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-28/dss

Peer Review File: Available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-28/prf

Conflicts of Interest: The authors have completed the ICMJE uniform disclosure form (available at https://jlpm.amegroups.org/article/view/10.21037/jlpm-24-28/coif). E.U. serves as an unpaid editorial board member of Journal of Laboratory and Precision Medicine from December 2023 to November 2025. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by our Institutional Ethics Research Committee (OSI Barrualde Comité de Etica en Investigación, reference No. 1055/22) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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