A comparison of the functional properties of two lepore hemoglobins with those of hemoglobin A1.

Lepore hemoglobins result from crossovers between normal beta and delta chain genes. Structural investigation of two newly discovered examples of Lepore hemoglobins revealed one of them to be structurally identical to hemoglobin Lepore Hollandia α₂^Aδ²² -x- β⁵⁰, a rarely occurring Lepore variant, while the second had the structure of hemoglobin Lepore Boston α₂^Aδ⁸⁷ -x- β¹¹⁶. Studies of the equilibrium and kinetic properties of the liganding reactions of these two Lepore hemoglobins, which differ only in three amino acid residues, and comparison of these with the known properties of hemoglobin A₁ (α₂β₂) and hemoglobin A₂ (α₂δ₂) have been carried out. A high value of n, the Hill coefficient, indicating normal heme-heme interaction, was observed in each hemoglobin along with a normal Bohr effect. However, a slight but definite increase in oxygen affinity was observed for each Lepore hemoglobin. Furthermore, kinetic studies indicated a slight but consistently increased rate of ligand combination and a somewhat decreased rate of oxygen dissociation for hemoglobins Lepore Hollandia and Lepore Boston at pH 7 and 20 °C. Apparently, the higher oxygen affinity of these Lepore hemoglobins over those of the normal hemoglobins A₁ and A₂ reflects changes of sequence that are common to both types of hemoglobin Lepore.     

Expression and Properties of Recombinant HbA2 (α2δ2) and Hybrids Containing δ-β Sequences

Hemoglobin A₂ (α₂δ₂), which is present at low concentration (1–2%) in the circulating red cells of normal individuals, has two important features that merit its study, i.e., it inhibits polymerization of sickle HbS and its elevated concentration in some thalassemias is a useful clinical diagnostic. However, reports on its functional properties regarding O₂ binding are conflicting. We have attempted to resolve these discrepancies by expressing, for the first time, recombinant hemoglobin A₂ and systematically studying its functional properties. The construct expressing HbA₂ contains only α and δ genes so that the extensive purification required to isolate natural HbA₂ is circumvented. Although natural hemoglobin A₂ is expressed at low levels in vivo, the amount of recombinant α₂δ₂ expressed in yeast is similar to that found for adult hemoglobin A and for fetal hemoglobin F when the α + β or the α + γ genes, respectively, are present on the construct. Recombinant HbA₂ is stable, i.e., not easily oxidized, and it is a cooperative functional hemoglobin with tetramer-dimer dissociation properties like those of adult HbA. However, its intrinsic oxygen affinity and response to the allosteric regulators chloride and 2,3-diphosphoglycerate are lower than the corresponding properties for adult hemoglobin. Molecular modeling studies which attempt to understand these properties of HbA₂ are described.     

Inhibitory effect of deoxyhemoglobin A2 on the rate of deoxyhemoglobin S polymerization.

From a consideration of the primary sequence of hemoglobin A₂ and the reported 5 å molecular contacts between deoxyhemoglobin S molecules in a crystal, it is predicted that hemoglobin A₂ might act as an inhibitor of the polymerization of deoxyhemoglobin S in a manner similar to hemoglobin. F. This has been tested experimentally by measuring the rate of change of the transverse water proton relaxation times (T₂) in equimolar mixtures of hemoglobin S and one of the non-gelling hemoglobins A, F or A₂. Hemoglobins A₂ and F have far more pronounced inhibitory effects on the rate of polymerization than does hemoglobin A. These molecules contain several amino acid differences from hemoglobin A beta chains which are located in the 5 Å molecular crystal contacts and these altered crystal contacts result in a much stronger inhibition of the rate of polymerization. Since hemoglobin A₂ is a normal hemoglobin found in small amounts in all adult red cells, increased delta chain synthesis may have potential importance in therapy for sickle cell disease.     

The binding of hemoglobin to membranes of normal and sickle erythrocytes

The binding of hemoglobins A, S, and A₂ to red cell membranes prepared by hypotonic lysis from normal blood and blood from persons with sickle cell anemia was quantified under a variety of conditions using hemoglobin labelled by alkylation with ¹⁴C-labelled Nitrogen Mustard. Membrane morphology was examined by electron microscopy. Normal membranes were found capable of binding native hemoglobin A and hemoglobin S in similar amounts when incubated at low hemoglobin: membrane ratios, but at high ratios hemoglobin saturation levels of the membranes increased progressively for hemoglobin A, hemoglobin S and hemoglobin A₂, respectively, in order of increasing electropositivity. Binding was unaffected by variations in temperature (4–22 °C) and altered little by the presence of sulfhydryl reagents, but was inhibited at pH levels above 7.35; disrupted at high ionic strength; and dependent on the ionic composition of the media. These findings suggest that electrostatic, but not hydrophobic or sulfhydryl bonds are important in membrane binding of the hemoglobin under the conditions studied.An increased retention of hemoglobin in preparations of membranes from red cells of patients with sickle cell anemia (homozygote S) was attributable to the dense fraction of homozygote S red cells rich in irreversibly sickled cells, and the latter membranes had a smaller residual binding capacity for new hemoglobin. This suggests that in homozygote S cells which have become irreversibly sickled cells in vivo, there are membrane changes which involve alteration and/or blockade of hemoglobin binding sites.These findings support the notion that hemoglobin participates in the dynamic structure of the red cell membrane in a manner which differs in normal and pathological states.     

Preadmission Glycemic Control and Changes to Diabetes Mellitus Treatment Regimen After Hospitalization

ObjectiveTo evaluate treatment patterns associated with diabetes medication regimen changes after hospitalization on the basis on preadmission hemoglobin A_1c levels.MethodsIn this retrospective database analysis, patients with a diabetes diagnosis, hospitalization, and documented hemoglobin A_1c level within the 90 days leading up to hospital admission were identified in an administrative claims database. Treatment regimens were assessed before and after hospitalization. The proportion of patients who had progression, reduction, or no change in therapy was compared across hemoglobin A_1c subgroups: hemoglobin A_1c < 7.0%, hemoglobin A_1c 7.0%-7.9%, and hemoglobin A_1c ≥ 8.0%.ResultsFour hundred patients were included (192 in hemoglobin A_1c < 7.0% group, 94 in hemoglobin A_1c 7.0% 7.9% group, and 114 in hemoglobin A_1c ≥ 8.0% group). Demographically, hemoglobin A_1c subgroups did not differ significantly (mean age, 57 years; 47.5% male). With respect to therapeutic regimen overall, 28%, 24%, and 48% of patients experienced progression, reduction, and no change, respectively. Across hemoglobin A_1c subgroups, 37.7% of patients in the hemoglobin A_1c ≥ 8.0% subgroup had therapy progression compared with 26% and 20.2% in the hemoglobin A_1c < 7.0% and hemoglobin A_1c 7.0%-7.9% subgroups, respectively (P = .032 and P = .006, respectively). Within the progression category, progression via insulin initiation was significantly higher in the hemoglobin A_1c ≥ 8.0% subgroup (55.8%) than in the hemoglobin A_1c < 7.0% subgroup (16%, P < .001), but not significantly higher than in the hemoglobin A_1c 7.0%-7.9% subgroup (36.8%, P = .084). In the hemoglobin A_1c ≥ 8.0% subgroup, a lower percentage of patients, 35.1%, experienced no therapy change than in both the hemoglobin A_1c < 7.0% subgroup (52.6%) and the hemoglobin A_1c 7.0%-7.9% subgroup (54.3%) (P = .003 and P = .006, respectively). There was no difference between subgroups in reduction of therapy.ConclusionsA higher proportion of patients with a hemoglobin A_1c level ≥ 8.0% had progression of their antidiabetes therapy after hospitalization and fewer patients had no change in therapy than those in lower hemoglobin A_1c subgroups. These data suggest that clinicians may be using hemoglobin A_1c measurements to guide discharge planning treatment decisions. (Endocr Pract. 2012;18:371-375)     

Ligand-dependent aggregation of chicken hemoglobin AI

The hemoglobin A_I component of the white leghorn chicken may potentially provide an animal model for the $\text{in vitro}$ aggregation behavior of human hemoglobin S. In solutions of low ionic strength, it has been found to undergo a striking loss of solubility upon deoxygenation, leading to the formation of macromolecular aggregates. This property is not shared by the other major chicken hemoglobin component, designated A_II. Compositional and NH₂-terminal sequence analysis indicate that extensive primary structural differences reside in the alpha chains of these two hemoglobins. The beta chains appear to be identical. Examination by electron microscopy suggests that the deoxyhemoglobin A_I forms microcrystalline arrays. The A_I component shows diminished reactivity with ¹³CO₂, as judged from ¹³C NMR measurements.     

An individual with “Miyada”-like hemoglobin indistinguishable from hemoglobin A2

The hemoglobin of a 24-year-old man of Italian descent who has the phenotypic characteristics of thalassemia intermedia contains about 12% hemoglobin F, 73% hemoglobin A, and 15% hemoglobin A₂. Chemical analysis definitely identifies the last as hemoglobin A₂. So elevated a percentage of hemoglobin A₂ has not been reported before. In addition, the amount of hemoglobin A is unusually large for an individual with presumed homozygosity for -thalassemia. Although the evidence is indirect, it is suggested that he is heterozygous for two conditions: -thalassemia and a Miyada type of gene that produces a hemoglobin indistinguishable from hemoglobin A₂.The work was supported in part by grants HL-02558 and HL-05168 and Training Grant HD-00048 from the National Institutes of Health, U.S. Public Health Service, as well as funds from the Southern California Chapter of the Cooley's Anemia Blood and Research Foundation.     

Method for the complete separation of radioactively labeled human γ-globin chains from pre-βA chains on CM-cellulose chromatography: Use of cold carrier globin chains

Carboxymethyl (CM)-cellulose chromatography of globins is the technique used most frequently in analysis of hemoglobin synthesis. However, if this method is to be reliable in cases where only small amounts of fetal hemoglobin (α₂γ₂) compared to adult hemoglobin (α₂β₂^A) are synthesized, it is important to obtain a clean separation of γ chains from pre-β^A chains. In the past, it has been found that small amounts of pre-β^A chains tend to elute with the γ chains. Radioactively labeled γ chains can be completely and reproducibly separated from small amounts of labeled pre-β^A chains by the addition of unlabeled β^J chains (Hb J Baltimore = β16 Gly → Asp) which elute at the same position as the pre β^A chains, thus increasing the quantity of this peak and allowing a clean separation from the γ chains.     

Some aspects of cooperativity in human hemoglobin

The cooperativity in hemoglobin can be described by the Hill parameter n, the free energy of interaction ΔF₁ and the allosteric free energy ΔF_A. By this latter is meant here the free energy change associated with the transition from the deoxy to the oxy conformation in hemoglobin. In this paper some general relations between n, ΔF₁ and ΔF_A are given. A method is presented by which ΔF_A can be calculated from oxygenation data.     

Studies on Respiratory Enzymes in Rice Kernel

Glutathione reductase as an acidic flavoprotein, has been isolated from the acidic protein fraction of rice embryos and purified by procedures involving ammonium sulfate fractionation, gel filration on Sephadex G–75 and G–100, ion exchange chromatography on CM-and DEAE-Sephadex and finally hydroxylapatite column chromatography. The preparation was homogeneous when examined by ultracentrifugation and almost pure on polyacrylamide gel electrophoresis. The flavoprotein exhibited an absorption spectrum characteristic of glutathione reductase having absorption maxima at 275, 370, 379, and 463 mμ with a clear double peak between 370 and 380 mμ and shoulders at around 430 and 490 mμ. The absorption ratio of A₂₇₅/A₄₆₃ and A₄₆₃/A₃₇₉ were 8.15 and 1.06, respectively. The purified enzyme was highly specific for NADPH and oxidized glutathione. The preparation had the average catalytic activity of 150 μmoles of NADPH oxidized per min per mg of protein.     

Autocrine factors in defense of cytotoxic CTLL-2 cells from oxidative stress

The role of pyruvate and autocrine polypeptide factors (APF) secreted by cytotoxic IL-2-dependent CTLL-2 cells in cell defense from oxidative stress was investigated. The addition of a conditioned medium (CM) containing pyruvate and APF into CTLL-2 cell cultures significantly increased the cell survival under oxidative stress conditions induced by hydrogen peroxide (H₂O₂). The kinetics of (H₂O₂) removal from cell cultures with added CM has been registered. It has been shown that, at the beginning of oxidative stress (less than 15 min), H₂O₂ was mostly removed by means of its reaction with pyruvate contained in CM. Pyruvate content in CM was estimated as 138 ± 7 μM. Gel filtration on a column with Bio-Gel P-10 was used to eliminate pyruvate from CM. Gel filtration resulted in three CM fractions (A, B, and C) corresponding to three chromatogram peaks. Pyruvate was not detected in any fraction. The fraction A was the first to be eluted from the column and contained the largest molecules. In the cell survival test, fraction B had the highest protective ability for CTLL-2 cells under oxidative stress. Fraction A supported cell survival to a lesser degree and fraction C did not show any protective abilities. Fraction B added to cells under oxidative stress kept intracellular ATP content at a significantly higher level then in control cells. Moreover, it was found that APF from fraction B was able to react with H₂O₂ directly and inactivate it in the absence of cells. APF from fraction A did not have such properties.     

Expression and properties of recombinant HbA2 (alpha2delta2) and hybrids containing delta-beta sequences

Hemoglobin A₂ (₂₂), which is present at low concentration (1–2%) in the circulating red cells of normal individuals, has two important features that merit its study, i.e., it inhibits polymerization of sickle HbS and its elevated concentration in some thalassemias is a useful clinical diagnostic. However, reports on its functional properties regarding O₂ binding are conflicting. We have attempted to resolve these discrepancies by expressing, for the first time, recombinant hemoglobin A₂ and systematically studying its functional properties. The construct expressing HbA₂ contains only and genes so that the extensive purification required to isolate natural HbA₂ is circumvented. Although natural hemoglobin A₂ is expressed at low levels in vivo, the amount of recombinant ₂₂ expressed in yeast is similar to that found for adult hemoglobin A and for fetal hemoglobin F when the + or the + genes, respectively, are present on the construct. Recombinant HbA₂ is stable, i.e., not easily oxidized, and it is a cooperative functional hemoglobin with tetramer-dimer dissociation properties like those of adult HbA. However, its intrinsic oxygen affinity and response to the allosteric regulators chloride and 2,3-diphosphoglycerate are lower than the corresponding properties for adult hemoglobin. Molecular modeling studies which attempt to understand these properties of HbA₂ are described.     

Impact of Race/Ethnicity on the Efficacy and Safety of Commonly used Insulin Regimens: A Post HOC Analysis of Clinical Trials in Type 2 Diabetes Mellitus

ObjectiveTo explore the impact of race/ethnicity on the efficacy and safety of commonly used insulin regimens in patients with type 2 diabetes mellitus.MethodsIn this post hoc analysis, pooled data from 11 multinational clinical trials involving 1455 patients with type 2 diabetes were used to compare specific insulin treatments in Latino/Hispanic, Asian, African-descent, and Caucasian patients. Insulin treatments included once daily insulin glargine or neutral protamine Hagedorn (BASAL), insulin lispro mix 75/25 twice daily (LMBID), or insulin lispro mix 50/50 three times daily (LMTID).ResultsRace/ethnicity was associated with significant outcome differences for each of the insulin regimens. BASAL therapy was associated with greater improvement in several measures of glycemic control among Latino/Hispanic patients compared with Caucasian patients (lower end point hemoglobin A1c, greater reduction in hemoglobin A1c from baseline, and a larger proportion of patients achieving hemoglobin A1c level < 7%). In contrast, LMBID therapy was associated with higher end point hemoglobin A_1c and a smaller decrease in hemoglobin A_1c from baseline in Latino/Hispanic and Asian patients than in Caucasian patients. Furthermore, fewer Asian patients attained a hemoglobin A_1c level < 7% than did Caucasians patients. For LMTID therapy, hemoglobin A_1c outcomes were comparable across patient groups. Fasting blood glucose and glycemic excursions varied among racial/ethnic groups for the 3 insulin regimens. Weight change was comparable among racial/ethnic groups in each insulin regimen. During treatment with LMTID, Asian patients experienced higher incidence and rate of severe hypoglycemia than Caucasian patients.ConclusionsLatino/Hispanic, Asian, and African-descent patients with type 2 diabetes show different metabolic responses to insulin therapy, dependent in part on insulin type and regimen intensity. (Endocr Pract. 2010: 818-828:pp)     

Markedly Low Hemoglobin A1c in a Patient with an Unusual Presentation of ß-Thalassemia Minor

ObjectiveTo describe very low hemoglobin A_1c levels in a patient with type 2 diabetes mellitus and an unusual presentation of β-thalassemia minor.MethodsWe present the clinical and laboratory findings of the study patient.ResultsA 64-year-old African American man with type 2 diabetes mellitus was referred to the endocrinology clinic with a hemoglobin A_1c level of 1.6% despite elevated blood glucose concentrations. A red blood cell survival study with chromium-51 revealed that he had a reduced erythrocyte life span less than 25% of normal. He also had a markedly elevated reticulocyte count ranging from 236 to 534 x 10³/μL (reference range, 25-75 x 103/μL). The laboratory findings, which are not characteristic of ß-thalassemia minor, could be the cause of the markedly low hemoglobin A_1c in this patient.ConclusionsAlthough rare, when associated with marked erythrocyte turnover, β-thalassemia minor can lead to a severe reduction in HbA_1c levels. In this scenario, glycemic control is best assessed by measuring fructosamine. (Endocr Pract. 2010;16:89-92)     

Kinetics of ligand binding to ferrous heme groups of hemoglobin MSaskatoon.

Hemoglobin M_Saskatoon (α₂^Aβ₂^63tyr) has two α chains in the normal ferrous state, while its two β chains are in the ferric state. The reaction of hemoglobin M_Saskatoon with carbon monoxide at pH 7 and 20 °C in the presence and absence of dithionite was studied. In the absence of dithionite only the α chains react and the combination rate is slow and similar to that of normal deoxyhemoglobin. After the addition of dithionite the rate of reaction is greatly increased initially and then decreases to a rate similar to that seen in the absence of dithionite. The dissociation of oxygen from hemoglobin M_Saskatoon at pH 7 and 20 °C was found for the α subunits to be similar to that seen for normal oxyhemoglobin. This similarity in the kinetic properties of normal hemoglobin and the α subunits of hemoglobin M_Saskatoon in both ligand combination and dissociation reactions indicates that the α subunits of hemoglobin M_Saskatoon undergo a structural transition from a low to high affinity form on liganding. Since the β subunits react rapidly with carbon monoxide even when the α subunits are unliganded, it appears that the ligand binding sites of the β chains are uncoupled from the state of liganding of the α subunits.     

Crystal structure analysis of sea lamprey hemoglobin at 2 Å resolution

The crystal structure of the predominant hemoglobin component of blood from the sea lamprey, Petromyzon marinus, has been determined by X-ray diffraction analysis. Crystals for this analysis were grown from cyanide methemoglobin V as crystal type D₂. These crystals are in space group P2₁2₁2₁ and have unit cell dimensions of $\text{a = 44.57}\text{A}\text{?}\text{, b = 96.62}\text{A}\text{?}\text{and}\text{c = 31.34}\text{A}\text{?}$. Isomorphous heavyatom derivatives were prepared by soaking crystals in solutions of Hg(CN)₂, K₂Hg(CNS)₄ and KAu(CN)₂. Diffracted intensities to as far as 2 Å spacings were measured on a diffractometer. Phases were found by means of the isomorphous replacements and anomalous scattering, with supplementary information provided by the tangent formula. An atomic model was fitted to the final electron density map in a Richards optical comparator. The lamprey hemoglobin molecule is generally similar in structure to other globins, but differs in many details. Each molecule is in contact with ten neighboring molecules in the crystal lattice. The nature of the binding of the heavy atoms to lamprey hemoglobin has been interpreted.     

Separation of solubilized alpha and beta adrenergic receptors by affinity chromatography.

Isoelectric focusing in the presence of Nonidet P-40 splits human chromatographically pure γ globin chains into two bands of isoelectric points 6.95 and 6.85, respectively. The comparison of the relative proportions of the two bands with the ratios between the G_γ and A_γ non allelic chains of human fetal hemoglobin suggests that the band at pI 6.95 corresponds to G_γ and the band at pI 6.85 corresponds to the A_γ chain; the latter is the only band present in a patient with Greek type hereditary persistence of fetal hemoglobin, producing only A_γ chains. Fluorography of electrofocusing-separated radioactive γ globin chains synthesized by thalassemic reticulocytes indicates that the relative $\text{G}{}_{\mathrm{\gamma }}\text{A}{}_{\mathrm{\gamma }}$ synthetic ratios are similar to the relative amounts of G_γ and A_γ chains accumulated in the erythrocytes, suggesting that the activities for the G_γ and A_γ mRNAs decay at roughly similar rates.     

Physical and immunochemical properties of low-buoyant-density proteoglycans from avian cartilage

A proteoglycan link fraction (A₁D₅) from avian xyphoid cartilage contains one link protein and low-buoyant-density proteoglycans. An antiserum made against this fraction (anti-A₁D₅ serum) specifically binds [³⁵S]sulfate-labeled proteoglycans from aggregate (A₁), monomer (A₁D₁), and link (A₁D₅) fractions synthesized by 14-day embryonic chick sterna. When [³⁵S]sulfate-labeled proteoglycans from either monomer (A₁D₁) or link (A₁D₅) fractions are used as the antigen, anti-A₁D₅ serum binds as well as an antiserum against a purified monomer preparation (anti-A₁D₁1400 Vo serum). However, reduction and alkylation of the proteoglycans from the monomer fraction does reveal differences in the binding of the two antisera. Whereas reduction and alkylation of the antigen (³⁵S-A₁D₁) inhibit binding by both antisera, binding of the anti-A₁D₅ serum is more affected by antigen alteration. Differences in the two antisera can also be detected in assays using labeled aggregate as antigen. Anti-A₁D₅ serum cannot maintain the same levels of antigen binding as the anti-A₁D₁-1400 Vo serum when compared in an antibody dilution curve. In addition, anti-A₁D₁-1400 Vo serum can stabilize aggregate during sedimentation in a sucrose density gradient containing 4 m guanidine hydrochloride whereas anti-A₁D₅ serum cannot. These results suggest that the low-buoyant-density proteoglycans found in the link (A₁D₅) fraction from avian cartilage contain some of the antigenic determinants found on the proteoglycan monomer. However, there is at least one monomer determinant which is not present in the A₁D₅ fraction.     

Analysis of the electron paramagnetic resonance spectrum of the cobalamin intermediate in ribonucleotide reduction

EPR absorption-derivative lineshapes have been computed and least-squares fitted to the spectrum of the intermediate derived from 5'-deoxy-5'-adenosyl-cobalamin in the ribonucleotide reductase reaction. A Gausian-type intrinsic lineshape was assumed and the effects of inhomogenous broadening, rotation of coordinate axes of the A-tensor relative to the g-tensor, angular dependence of transition probability and ligand hyperfine splitting have also been investigated.When the overall spectrum was computed as the sum of the linshapes corresponding to two distinct Co(II) species, A and B, each having rhombic asymmetry, the least squares procedure converged to a much better fit than with a single species, and matched almost all of the features of the experimental spectrum.The magnetic properties of A and B were compared with those of a series of other Co(II) complexes by a plot of g_|?g₆ versus ∥A₆∥?∥A_|∥. The results eliminate cobalt with 5-coordination to nitrogen for A and B, suggest low-spin cobalt complexes having strongly distorted 6-fold coordination. The possibility that the sixth, symmetry-decreasing ligand is the oxygen molecule is excluded by the chemistry of the system and by the EPR properties of previously reported cob(II)alamins. It is suggested that the sixth ligand is carbonyl, amide or sulfhydryl group of an enzyme sidechain which is inserted off-axis into the coordination position so as to exert the observed symmetry-lowering effect.     

Ethnic disparity in hemoglobin A1c levels among normoglycemic offspring of parents with type 2 diabetes mellitus

ObjectiveTo investigate the racial/ethnic disparities in hemoglobin A_1c levels among nondiabetic persons with similar parental history of type 2 diabetes mellitus.MethodsWe studied a community-based sample of adult offspring of parents with type 2 diabetes mellitus. Measurements included anthropometry, hematology assessments, serial fasting plasma glucose, oral glucose tolerance testing, plasma insulin, hemoglobin A_1c, insulin sensitivity, and b-cell function, using a homeostasis model assessment.ResultsThe study included 302 participants (135 white, 167 black). Compared with white participants, black participants had lower fasting plasma glucose levels (91.9 ± 0.51 mg/dL vs 93.6 ± 0.50 mg/dL, P = .015), lower area under the curve of plasma glucose during oral glucose tolerance testing (P = <.001), higher body mass index (31.1 ± 0.61 kg/m² vs 28.5 ± 0.57 kg/m², P = <.001), and similar insulin sensitivity and b-cell function. Hemoglobin A_1c was higher in black participants than in white participants (5.68 ± 0.033% vs 5.45 ± 0.028%, P <.001). The absolute black-white difference in hemoglobin A_1c level of approximately 0.22% persisted after adjusting for age, hemoglobin, hematocrit, body mass index, waist circumference, fasting plasma glucose, glucose area under the curve, and other covariates.ConclusionsAmong healthy offspring of parents with type 2 diabetes mellitus in this study, African American participants had higher hemoglobin A_1c levels than white participants after adjusting for age, adiposity, blood glucose, and known variables. Thus, plasma glucose level is more valid than hemoglobin A_1c for diagnosing prediabetes or diabetes in black persons. (Endocr Pract. 2012; 18:356-362)