Use of an oral stable isotope label to confirm variation in red blood cell mean age that influences HbA1c interpretation

Relationship between red blood cell lifespan and endogenous carbon monoxide in the common bottlenose dolphin and beluga

Certain deep-diving marine mammals [i.e., northern elephant seal (Mirounga angustirostris), Weddell seal (Leptonychotes weddellii)] have blood carbon monoxide (CO) levels that are comparable with those of chronic cigarette smokers. Most CO produced in humans is a byproduct of heme degradation, which is released when red blood cells (RBCs) are destroyed. Elevated CO can occur in humans when RBC lifespan decreases. The contribution of RBC turnover to CO concentrations in marine mammals is unknown. Here, we report the first RBC lifespans in two healthy marine mammal species with different diving capacities and heme stores, the shallow-diving bottlenose dolphin (Tursiops truncatus) and deep-diving beluga whale (Delphinapterus leucas), and we relate the lifespans to the levels of CO in blood and breath. The belugas, with high blood heme stores, had the longest mean RBC lifespan compared with humans and bottlenose dolphins. Both cetacean species were found to have three times higher blood CO content compared with humans. The estimated CO production rate from heme degradation indicates some marine mammals may have additional mechanisms for CO production, or delay CO removal from the body, potentially from long-duration breath-holds.NEW & NOTEWORTHY This is the first study to determine the red blood cell lifespan in a marine mammal species. High concentrations of carbon monoxide (CO) were found in the blood of bottlenose dolphins and in the blood and breath of belugas compared with healthy humans. Red blood cell turnover accounted for these high levels in bottlenose dolphins, but there may be alternative mechanisms of endogenous CO production that are contributing to the CO concentrations observed in belugas.

A light scatter based model relating erythrocyte vesiculation to lifetime in circulation

Methods for measuring erythrocyte age distribution are not available as a simple analytical tool. Most of them utilize the fluorescence or radioactive isotopes labeling to construct the age distribution and support physicians with aging indices of donor's erythrocytes. The age distribution of erythrocyte may be a useful snapshot of patient state over 120-days period of life. Previously, we introduced the enhanced assay of erythrocytes with measurement of 48 indices in four categories: concentration/content, morphology, aging and function (10.1002/cyto.a.24554). The aging category was formed by the indices based on the evaluation of the derived age of individual cells. The derived age does not exactly mean the real age of erythrocytes and its evaluation utilizes changes of cellular morphology during a lifespan. In this study, we are introducing the improved methodological approach that allows us to retrieve the derived age of individual erythrocytes, to construct the aging distribution, and to reform the aging category consisting of eight indices. The approach is based on the analysis of the erythrocyte vesiculation. The erythrocyte morphology is analyzed by scanning flow cytometry that measures the primary characteristics (diameter, thickness, and waist) of individual cells. The surface area (S) and sphericity index (SI) are calculated from the primary characteristics and the scattering diagram SI versus S is used in the evaluation of the derived age of each erythrocyte in a sample. We developed the algorithm to evaluate the derived age that provides eight indices in the aging category based on a model using light scatter features. The novel erythrocyte indices were measured for simulated cells and blood samples of 50 donors. We determined the first-ever reference intervals for these indices.

Measurement of Erythrocyte Lifespan Using a CO Breath Test in Patients with Thalassemia and the Impact of Treatment

Background: Thalassemia comprises a diverse group of genetic disorders that affects the synthesis of globin chains, with a global distribution. The use of erythrocyte lifespan (ELS) to assess differences among patients with different types of thalassemia and the efficacy of splenectomy has not been implemented.  

Diabetes detection in women with gestational diabetes and polycystic ovarian syndrome

Gestational diabetes mellitus (GDM) and polycystic ovarian syndrome (PCOS) represent two of the highest risk factors for development of type 2 diabetes mellitus in young women. As these increasingly common conditions generally affect younger women, early detection of dysglycemia is key if preventative measures are to be effective. While international guidance recommends screening for type 2 diabetes, current screening strategies suffer from significant challenges.First, guidance lacks consensus in defining which tests to use and frequency of monitoring, thereby sending mixed messages to healthcare professionals.Second, conformity to guidance is poor, with only a minority of women having tests at the recommended frequency (where specified). Approaches to improve conformity have focused on healthcare related factors (largely technology driven reminder systems), but patient factors such as convenience and clear messaging around risk have been neglected.Third, and most critically, current screening strategies are too generic and rely on tests that become abnormal far too late in the trajectory towards dysglycemia to offer opportunities for effective preventative measures. Risk factors show wide interindividual variation, and insulin sensitivity and β cell function are often abnormal during pre-diabetes stage, well before frank diabetes.New, consistent, targeted screening strategies are required that incorporate early, prevention focused testing and personalised risk stratification.

Protein glycation in diabetes mellitus

Diabetes mellitus is the ninth leading cause of mortality worldwide. It is a complex disease that manifests as chronic hyperglycemia. Glucose exposure causes biochemical changes at the proteome level as reflected in accumulation of glycated proteins. A prominent example is hemoglobin A1c (HbA1c), a glycated protein widely accepted as a diabetic indicator. Another emerging biomarker is glycated albumin which has demonstrated utility in situations where HbA1c cannot be used. Other proteins undergo glycation as well thus impacting cellular function, transport and immune response. Accordingly, these glycated counterparts may serve as predictors for diabetic complications and thus warrant further inquiry. Fortunately, modern proteomics has provided unique analytic capability to enable improved and more comprehensive exploration of glycating agents and glycated proteins. This review broadly covers topics from epidemiology of diabetes to modern analytical tools such as mass spectrometry to facilitate a better understanding of diabetes pathophysiology. This serves as an attempt to connect clinically relevant questions with findings of recent proteomic studies to suggest future avenues of diabetes research.

Red Blood Cell Lifespan < 74 Days Can Clinically Reduce Hb1Ac Levels in Type 2 Diabetes

Variations in the red blood cell (RBC) lifespan can affect glycosylated hemoglobin (HbA1c) test values, but there is still a lack of evidence regarding how and to what degree the RBC lifespan influences HbA1c in the type 2 diabetes mellitus (T2DM) population owing to the restriction of traditional RBC lifespan detection means. In this study, we monitored 464 T2DM patients and 231 healthy control finger blood glucose levels at seven time points for three consecutive months. The HbA1c levels were assessed at the end of the third month as well as the RBC lifespan was measured through the CO breath test. T2DM patients were stratified into four quartile groups according to their RBC lifespans. There was no statistical significance in HbA1c among these four groups. However, the average blood glucose in the Q1 group was significantly higher than those in the other groups. Additionally, the contribution of RBC lifespan to HbA1c test value in the Q1 group was 14.07%, which was significantly higher than those in the other groups. Finally, we used multiple linear regression models to construct a mathematical formula to correct the HbA1c test value in the Q1 group, which would benefit the management of T2DM.

Variation in the hemoglobin glycation index

A high hemoglobin glycation index (HGI) has been repeatedly associated with greater risk for hypoglycemia in people with diabetes and greater risk for chronic vascular disease in people with or without diabetes. This review explores how different sources of analytical and biological variation in HbA1c and blood glucose individually and collectively affect the clinical information value of HGI. We conclude that HGI is a complex quantitative trait that is a clinically practical biomarker of risk for both hypoglycemia and chronic vascular disease.

Labile glycated hemoglobin: an underestimated laboratory marker of short term glycemia

OBJECTIVES

Diabetes mellitus is a major public health problem. Hemoglobin A_1c (HbA_1c) is a key laboratory parameter in the management of diabetes patients. However, in diabetes monitoring, interpretation of HbA_1c results is hampered by the important interindividual variation in red blood cell (RBC) life span. Furthermore, HbA_1c only slowly responds to changes in glucose metabolism. Besides HbA_1c, there exists a labile HbA_1c fraction (l-HbA_1c), exhibiting much faster kinetics. As both HbA_1c and l-HbA_1c are measured by modern standard chromatography, we explored the possibilities of using the l-HbA_1c fraction for monitoring glycemia.

METHODS

l-HbA_1c and HbA_1c fractions were simultaneously assayed on a Tosoh G8 analyzer and expressed as %. l-HbA_1c results were compared with serum glucose and HbA_1c. Concomitantly, RBC distribution width (RDW) was determined on a Sysmex SN analyzer as a marker for erythrocyte life span.

RESULTS

l-HbA_1c could be measured with between-run coefficient of variations (CVs) between 2.2 and 2.3%. l-HbA_1c correlated with both glycemia (r=0.80) and HbA_1c results (r=0.73). In a multiple regression model (r²=0.752), glycemia and HbA_1c were the most determining factors. To a lesser extent, RDW correlated with l-HbA_1c (r=0.158). Furthermore, the l-HbA_1c/HbA_1c ratio weakly positively correlated with RDW (r=0.247).

CONCLUSIONS

L-HBA_1c represents an additional marker for monitoring the rapid occurrence of glycemic disorders that escape detection when using only HbA_1c and blood glucose. RDW can be used as an indicator of atypical RBCs life span, in which the l-HbA_1c fraction may be helpful.

Comparison of Levitt's CO breath test and the 15 N-glycine labeling technique for measuring the lifespan of human red blood cells

The red blood cell (RBC) lifespan is an important physiological indicator of clear significance in clinical research, used for the differential diagnosis of various diseases such as anemia, compensatory phase hemolysis, and polycythemia. The ¹⁵ N-glycine labeling technique is the gold standard method for determining RBC lifespans. However, the usefulness of this technique in clinical settings is seriously hindered by the several weeks required to complete the analyses. Levitt's CO breath test is another reliable technique for determining RBC lifespans, with a simpler protocol giving much faster results, making it more useful in clinical applications. We compared the CO breath test and ¹⁵ N-glycine labeling technique for measuring the human RBC lifespan. We investigated human RBC lifespans where each subject undertook both the ¹⁵ N-glycine labeling technique and the CO breath test. The correlation between the results from these two methods was analyzed. Eight of the ten subjects successfully completed the study. The RBC lifespan values obtained by Levitt's CO breath test were lower than those obtained by the ¹⁵ N-glycine labeling technique. The RBC lifespan values determined from the ¹⁵ N-glycine labeling technique and the CO breath test were significantly correlated, with a Pearson correlation coefficient of R = 0.98 (p < 0.05), while the R² of the linear regression equation was 0.96. The CO breath test exhibits as good performance as the ¹⁵ N-glycine labelling technique in distinguishing healthy subjects from subjects with hemolysis. The result suggests that the CO breath test is a reliable method for quickly determining human RBC lifespans in clinical applications.

Comparative study on hemoglobin A1c, glycated albumin and glycosylated serum protein in aplastic anemia patients with Type 2 diabetes mellitus

Objective: To differentiate the value of hemoglobin A1c (HbA1c), glycated albumin (GA) and glycosylated serum protein (GSP) in monitoring blood glucose of patients with aplastic anemia.

Methods: 42 patients with aplastic anemia (AA) and 30 patients with AA and Type 2 diabetes mellitus (T2DM) were enrolled in the study, in comparison with 114 healthy subjects and 88 subjects with T2DM. HbA1c, GA, GSP, fasting plasma glucose (FPG), hemoglobin (Hb) and albumin (ALB) were measured, and group comparison and correlation analysis were carried out.

Results: Compared with the non-diabetes patients while ALB were <30 g/l or 30–40 g/l, the HbA1c and GSP values in AA, T2DM and AA+T2DM patients were significantly higher while the GA values were lower. Moreover, no differences in FPG levels. The AA+T2DM patients with ALB >40 g/l had higher HbA1c level, with no difference in GA, GSP and FPG levels. There was a positive correlation between HbA1c and GA in healthy group (ALB ≥ 40 g/l), AA patients (ALB 30–40 g/l and ≥40 g/l), T2DM patients (ALB 30–40 g/l and ≥40 g/l) and AA+T2DM patients (ALB 30–40 g/l and ≥40 g/l) but not in those with ALB < 30 g/l.

Conclusion: The HbA1c results were affected by moderate-to-severe anemia, but not mild anemia. HbA1c is not recommended to detect blood glucose levels in AA patients (Hb < 90 g/l) or AA patients (ALB < 30 g/l). FPG and GSP are not suitable for AA patients.

How Do Red Blood Cells Die?

Normal human red blood cells have an average life span of about 120 days in the circulation after which they are engulfed by macrophages. This is an extremely efficient process as macrophages phagocytose about 5 million erythrocytes every second without any significant release of hemoglobin in the circulation. Despite large number of investigations, the precise molecular mechanism by which macrophages recognize senescent red blood cells for clearance remains elusive. Red cells undergo several physicochemical changes as they age in the circulation. Several of these changes have been proposed as a recognition tag for macrophages. Most prevalent hypotheses for red cell clearance mechanism(s) are expression of neoantigens on red cell surface, exposure phosphatidylserine and decreased deformability. While there is some correlation between these changes with aging their causal role for red cell clearance has not been established. Despite plethora of investigations, we still have incomplete understanding of the molecular details of red cell clearance. In this review, we have reviewed the recent data on clearance of senescent red cells. We anticipate recent progresses in in vivo red cell labeling and the explosion of modern proteomic techniques will, in near future, facilitate our understanding of red cell senescence and their destruction.

Reduced erythrocyte lifespan measured by chromium-51 in patients with type 2 diabetes undergoing long-term hemodialysis

INTRODUCTION

A reduced erythrocyte lifespan potentially explains the low hemoglobin A1c values found in hemodialysis patients. However, data supporting this notion in patients with type 2 diabetes is unclear. We evaluated the erythrocyte lifespan in patients with type 2 diabetes undergoing long-term hemodialysis and investigated potential predictors of erythrocyte lifespan.

METHODS

Long-term hemodialysis patients with type 2 diabetes and type 2 diabetes patients without nephropathy (estimated glomerular filtration rate > 60 mL/min/1.73 m² ) were included. The erythrocyte lifespan was measured using chromium-51 (⁵¹ Cr)-labeled erythrocytes. Blood radiotracer activity was measured six to nine times over a period of 3-5 weeks to determine the erythrocyte lifespan of each patient. Biochemical markers were obtained five times over 16 weeks and associated with the erythrocyte lifespan.

FINDINGS

Type 2 diabetes patients undergoing hemodialysis (N = 13) had a significantly shorter median erythrocyte lifespan of 49.7 (interquartile range [IQR] = 44.1-58.6) days compared with 64.2 (IQR = 62.6-83.5) days in the control group (N = 10) (P ˂ 0.001) with a difference between medians of 14.5 (95% confidence interval = 8.1-38.8) days. In the hemodialysis group, no association could be detected between the erythrocyte lifespan and markers of hemolysis, level of inflammation, or urea.

DISCUSSION

A reduced erythrocyte lifespan was detected in type 2 diabetes patients undergoing long-term hemodialysis. This may contribute to the reduced hemoglobin A1c values observed in the type 2 diabetic hemodialysis population. An association could not be detected between the erythrocyte lifespan and biochemical markers of hemolysis or inflammation.

Rationale and Design for a GRADE Substudy of Continuous Glucose Monitoring

Background: The Glycemia Reduction Approaches in Diabetes: A Comparative Effectiveness (GRADE) study has enrolled a racially and ethnically diverse population with type 2 diabetes, performed extensive phenotyping, and randomly assigned the participants to one of four second-line diabetes medications. The continuous glucose monitoring (CGM) substudy has been added to determine whether there are racial/ethnic differences in the relationship between average glucose (AG) and hemoglobin A1c (HbA1c). CGM will also be used to compare time in target range, glucose variability, and the frequency and duration of hypoglycemia across study groups. Methods: The observational CGM substudy will enroll up to 1800 of the 5047 GRADE study participants from the four treatment groups, including as many as 450 participants from each of 4 racial/ethnic minority groups to be compared: Hispanic White, non-Hispanic White, non-Hispanic African American, and non-Hispanic Other. CGM will be performed for 2 weeks in proximity to a GRADE annual visit, during which an oral glucose tolerance test will be performed and HbA1c and glycated albumin measured. Indicators of interindividual variation in red blood cell turnover, based on specialized erythrocyte measurements, will also be measured to explore the potential causes of interindividual HbA1c variations. Conclusions: The GRADE CGM substudy will provide new insights into whether differences exist in the relationship between HbA1c and AG among different racial/ethnic groups and whether glycemic profiles differ among frequently used diabetes medications and their potential clinical implications. Understanding such differences is important for clinical care and adjustment of diabetes medications in patients of different races or ethnicities.

Superiority of glycated albumin over glycated haemoglobin as indicator of glycaemic control and predictor of all-cause mortality in patients with type 2 diabetes mellitus receiving peritoneal dialysis

Background

Glycated albumin, in contrast to glycated haemoglobin, precisely reflects glycaemic control and predicts all-cause mortality in haemodialysis patients with diabetes mellitus. However, whether those associations exist in diabetes mellitus patients receiving peritoneal dialysis remains unclear.

Methods

This was a retrospective cross-sectional and longitudinal observational study. We measured glycated albumin, glycated haemoglobin and casual plasma glucose for two months in diabetes mellitus-peritoneal dialysis ( n = 44) and diabetes mellitus-haemodialysis ( n = 88) patients (age-, gender-matched). The diabetes mellitus-peritoneal dialysis patients were followed for three years to monitor occurrence of all-cause mortality.

Results

Glycated albumin and glycated albumin/casual plasma glucose ratios, but not casual plasma glucose, glycated haemoglobin, or glycated haemoglobin/casual plasma glucose, were significantly lower in the diabetes mellitus-peritoneal dialysis as compared with the diabetes mellitus-haemodialysis patients. The regression lines between casual plasma glucose and glycated albumin showed a significant parallel shift downwards in diabetes mellitus-peritoneal dialysis as compared with diabetes mellitus-haemodialysis patients, while the slope did not differ significantly between the groups, resulting in underestimation of glycaemic control by 4.5%. Kapan-Meier analysis of the diabetes mellitus-peritoneal dialysis patients revealed that higher glycated albumin (median >18.0%), but not glycated haemoglobin (median >6.6%), indicated significantly elevated risk for all-cause mortality, which occurred in 15 patients (34.1%), as compared with those with a lower glycated albumin concentration. Higher glycated albumin concentration was also significantly and independently associated with all-cause mortality in multivariate Cox proportional hazards analysis.

Conclusions

Glycated albumin, in contrast to glycated haemoglobin, more precisely reflects glycaemic control in diabetes mellitus-peritoneal dialysis patients, based on its significant association with all-cause mortality. Furthermore, adjustment of the true glycated albumin concentration by adding 4.5% might provide a more precise measurement for determining glycaemic control in such patients.

Glycosylated Hemoglobin in Subjects Affected by Iron-Deficiency Anemia

Previous studies have suggested that iron-deficiency anemia affects glycosylated hemoglobin (HbA1c) measurements, but the results were contradictory. We conducted a retrospective case-control study to determine the effects of iron deficiency on HbA1c levels. Starting with the large computerized database of the Italian Hospital of Desio, including data from 2000 to 2016, all non-pregnant individuals older than 12 years of age with at least one measurement of HbA1c, cell blood count, ferritin, and fasting blood glucose on the same date of blood collection were enrolled. A total of 2,831 patients met the study criteria. Eighty-six individuals were diagnosed with iron-deficiency anemia, while 2,745 had a normal iron state. The adjusted means of HbA1c were significantly higher in anemic subjects (5.59% [37.37 mmol/mol]), than those measured in individuals without anemia (5.34% [34.81 mmol/mol]) (P<0.0001). These results suggest that clinicians should be cautious about diagnosing prediabetes and diabetes in individuals with anemia.

When HbA1c and Blood Glucose Do Not Match: How Much Is Determined by Race, by Genetics, by Differences in Mean Red Blood Cell Age?

Commentary placing genetic ancestry markers and racial difference in HbA1c in the context of more common variations in the HbA1c-average glucose relationship and their clinical implications.

HbA1c method performance: The great success story of global standardization

Diagnosing and monitoring the treatment of people with diabetes is a global issue and uses considerable resources in laboratories and clinics worldwide. Hemoglobin A1c (HbA1c) has been the mainstay of monitoring glycemic control in people with diabetes for many years and more recently it has been advocated as a diagnostic tool for type 2 diabetes mellitus (T2DM). Good analytical performance is key to the successful use of any laboratory test, but is critical when using the test to diagnose disease, especially when the potential number of diagnoses could exceed 500 million people. Very small variations in bias or increased imprecision could lead to either a missed diagnosis or overdiagnosis of the disease and given the scale of the global disease burden, this could mean erroneous categorization of potentially millions of people. Fundamental to good performance of diagnostic testing is standardization, with defined reference materials and measurement procedures. In this review, we discuss the historical steps to first harmonize HbA1c testing, followed by the global standardization efforts and provide an update on the current situation and future goals for HbA1c testing.

Development, validation, and potential applications of biotinylated red blood cells for posttransfusion kinetics and other physiological studies: evidenced-based analysis and recommendations

The current reference method in the United States for measuring in vivo population red blood cell (RBC) kinetics utilizes chromium-51 (⁵¹ Cr) RBC labeling for determining RBC volume, 24-hour posttransfusion RBC recovery, and long-term RBC survival. Here we provide evidence supporting adoption of a method for kinetics that uses the biotin-labeled RBCs (BioRBCs) as a superior, versatile method for both regulatory and investigational purposes. RBC kinetic analysis using BioRBCs has important methodologic, analytical, and safety advantages over ⁵¹ Cr-labeled RBCs. We critically review recent advances in labeling human RBCs at multiple and progressively lower biotin label densities for concurrent, accurate, and sensitive determination of both autologous and allogeneic RBC population kinetics. BioRBC methods valid for RBC kinetic studies, including successful variations used by the authors, are presented along with pharmacokinetic modeling approaches for the accurate determination of RBC pharmacokinetic variables in health and disease. The advantages and limitations of the BioRBC method-including its capability of determining multiple BioRBC densities simultaneously in the same individual throughout the entire RBC life span-are presented and compared with the ⁵¹ Cr method. Finally, potential applications and limitations of kinetic BioRBC determinations are discussed.

Human erythrocyte lifespan measured by Levitt's CO breath test with newly developed automatic instrument

Existing standard techniques for erythrocyte (RBC) lifespan measurement, such as quantitation of labeling with isotopes or biotin, are cumbersome and time-consuming. Given that endogenous CO originates mainly from degraded RBCs, a team lead by Levitt developed a CO breath test to enable more efficient RBC lifespan estimation. The purpose of this study was to evaluate the reliability of Levitt's CO breath test method with our newly developed automatic instrument. RBC lifespan measurements conducted by Levitt's CO breath test method were conducted in 109 healthy subjects and 91 patients with chronic hemolytic anemia. In healthy subjects, the RBC lifespan was 126 ± 26 days, similar to values obtained with classical standard labeling methods. RBC lifespan did not differ significantly between males and females or between juveniles and adults, and did not correlate with age. To our knowledge, this datum represents an RBC lifespan average for the largest sample to date. In subjects with hemolytic anemia, RBC lifespan was 29 ± 14 days, which is significantly shorter than that of the healthy subjects (p = 0.001). Using 75 days as a cut-off, diagnostic accuracy for hemolytic anemia in the present study sample was 100%. In conclusion, the present results indicate that Levitt's CO breath test is an ideal method for human RBC lifespan measurement, and the newly developed automatic instrument is reliable and convenient for clinical practice.

Biochemical surrogate markers of hemolysis do not correlate with directly measured erythrocyte survival in sickle cell anemia

Hemolysis is a key feature of sickle cell anemia (HbSS). Direct quantitation of hemolysis could be used as an objective outcome in clinical trials of new therapeutics for HbSS and would also enable better human studies of the pathogenesis of complications of HbSS that are ostensibly hemolysis-related, such as pulmonary hypertension. However, contemporary human studies in HbSS have used only surrogate markers of hemolysis rather than direct measurements of RBC survival. We directly quantified hemolysis in HbSS by measuring survival of an age cohort of RBCs labeled with a stable isotope, administered orally as ¹⁵ N-glycine, a metabolic precursor of heme. The atomic excess of ¹⁵ N in heme extracted from blood was monitored by mass spectrometry over time. We performed 13 labeling experiments in 11 individuals with HbSS. Mean RBC survival was 31.9 days (range 14.1-53.6). Both HbF level, a known determinant of hemolysis, and absolute reticulocyte count (ARC), an index of the marrow's response to hemolysis, correlated with directly measured RBC survival (r = 0.61, P < 0.002; r = -0.84, P < 0.001). However, commonly used biochemical surrogates of hemolysis (LDH, AST, bilirubin, and plasma free hemoglobin) did not correlate with directly measured RBC survival. These biochemical surrogates should be interpreted cautiously, at best, in clinical trials and human physiologic studies in HbSS. ARC was the best correlate of total hemolysis, but only 70% of the variation in RBC survival was reflected in this marker. If greater accuracy is required in human studies, ¹⁵ N-glycine RBC labeling can directly and accurately quantify hemolysis. Am. J. Hematol. 91:1195-1201, 2016. © 2016 Wiley Periodicals, Inc.

Mechanistic modeling of hemoglobin glycation and red blood cell kinetics enables personalized diabetes monitoring

The amount of glycated hemoglobin (HbA1c) in diabetic patients' blood provides the best estimate of the average blood glucose concentration over the preceding 2 to 3 months. It is therefore essential for disease management and is the best predictor of disease complications. Nevertheless, substantial unexplained glucose-independent variation in HbA1c makes its reflection of average glucose inaccurate and limits the precision of medical care for diabetics. The true average glucose concentration of a nondiabetic and a poorly controlled diabetic may differ by less than 15 mg/dl, but patients with identical HbA1c values may have true average glucose concentrations that differ by more than 60 mg/dl. We combined a mechanistic mathematical model of hemoglobin glycation and red blood cell kinetics with large sets of within-patient glucose measurements to derive patient-specific estimates of nonglycemic determinants of HbA1c, including mean red blood cell age. We found that between-patient variation in derived mean red blood cell age explains all glucose-independent variation in HbA1c. We then used our model to personalize prospective estimates of average glucose and reduced errors by more than 50% in four independent groups of greater than 200 patients. The current standard of care provided average glucose estimates with errors >15 mg/dl for one in three patients. Our patient-specific method reduced this error rate to 1 in 10. Our personalized approach should improve medical care for diabetes using existing clinical measurements.

A Novel Physiology-Based Mathematical Model to Estimate Red Blood Cell Lifespan in Different Human Age Groups

Direct measurement of red blood cell (RBC) survival in humans has improved from the original accurate but limited differential agglutination technique to the current reliable, safe, and accurate biotin method. Despite this, all of these methods are time consuming and require blood sampling over several months to determine the RBC lifespan. For situations in which RBC survival information must be obtained quickly, these methods are not suitable. With the exception of adults and infants, RBC survival has not been extensively investigated in other age groups. To address this need, we developed a novel, physiology-based mathematical model that quickly estimates RBC lifespan in healthy individuals at any age. The model is based on the assumption that the total number of RBC recirculations during the lifespan of each RBC (denoted by N max) is relatively constant for all age groups. The model was initially validated using the data from our prior infant and adult biotin-labeled red blood cell studies and then extended to the other age groups. The model generated the following estimated RBC lifespans in 2-year-old, 5-year-old, 8-year-old, and 10-year-old children: 62, 74, 82, and 86 days, respectively. We speculate that this model has useful clinical applications. For example, HbA1c testing is not reliable in identifying children with diabetes because HbA1c is directly affected by RBC lifespan. Because our model can estimate RBC lifespan in children at any age, corrections to HbA1c values based on the model-generated RBC lifespan could improve diabetes diagnosis as well as therapy in children.

Physiologic Concepts That May Revise the Interpretation and Implications of HbA1C in Clinical Medicine: An American Perspective

HbA1c, a routinely used integrated measure of glycemic control, is traditionally thought to be equivalent to mean blood glucose in hematologically normal individuals. Therefore, particularly as the methodology of measuring HbA1c has been standardized, clinical decisions dependent on mean blood glucose are often predominantly decided based on the interpretation of measured HbA1c. In this commentary, however, now that a more routine method of measuring red cell life span has been developed, we present evidence that the relationship between HbA1c and mean blood glucose is influenced by variation in red blood cell survival even in the hematologically normal. This variation has consequences for the appropriate interpretation of HbA1c in diverse clinical conditions such as the diagnosis of diabetes and management of diabetes in chronic kidney disease.