Spuriously High Prevalence of Prediabetes Diagnosed by HbA1c in Young Indians Partly Explained by Hematological Factors and Iron Deficiency Anemia

PALLAVI S. HARDIKAR BMTECH SUYOG M. JOSHI MSC DATTATRAY S. BHAT MSC DEEPA A. RAUT BMTECH PRACHI A. KATRE MSC HIMANGI G. LUBREE MSC ABHAY JERE PHD ANAND N. PANDIT CAROLINE H.D. FALL MB CHB DM FRCPH CHITTARANJAN S. YAJNIK E p i d e m i o l o g y / H e a l t h OBJECTIVEdTo examine the influence of glycemic and nonglycemic parameters on HbA1c concentrations in young adults, the majority of whom had normal glucose tolerance. RESEARCH DESIGN AND METHODSdWe compared the diagnosis of normal glucose tolerance, prediabetes, and diabetes between a standard oral glucose tolerance test (OGTT; World Health Organization 2006 criteria) and HbA1c concentrations (American Diabetes Association [ADA] 2009 criteria) in 116 young adults (average age 21.6 years) from the Pune Children's Study. We also studied the contribution of glycemic and nonglycemic determinants to HbA1c concentrations. RESULTSdThe OGTT showed that 7.8% of participants were prediabetic and 2.6% were diabetic. By ADA HbA1c criteria, 23.3% were prediabetic and 2.6% were diabetic. The negative predictive value of HbA1c was 93% and the positive predictive value was 20% (only 20% had prediabetes or diabetes according to the OGTT; this figure was 7% in anemic participants). Of participants, 34% were anemic, 37% were iron deficient (ferritin ,15 ng/mL), 40% were vitamin B12 deficient (,150 pmol/L), and 22% were folate deficient (,7 nmol/L). On multiple linear regression analysis, HbA1c was predicted by higher 2-h glucose (R2 = 25.6%) and lower hemoglobin (R2 = 7.7%). When hematological parameters were replaced by ferritin, vitamin B12, and folate, HbA1c was predicted by higher glycemia (R2 = 25.6%) and lower ferritin (R2 = 4.3%). CONCLUSIONSdThe use of HbA1c to diagnose prediabetes and diabetes in iron-deficient populations may lead to a spuriously exaggerated prevalence. Further investigation is required before using HbA1c as a screening tool in nutritionally compromised populations. - T abetes and diabetes is an attractive he use of HbA1c to diagnose predioption in prospective epidemiological studies because it may avoid the need for repeated oral glucose tolerance tests (OGTTs). The American Diabetes Association (ADA) and World Health Organization (WHO) have recently approved the use of HbA1c for screening and diagnosis of diabetes (13). Both organizations have suggested that concentrations $6.5% be considered diabetes, and the ADA has c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c suggested 5.76.4% as diagnostic of prediabetes (3). The concentration of HbA1c depends on not only prevailing glycemia but also the life span of erythrocytes. Nutritional deficiencies are a major factor affecting erythrocyte survival. Among these, iron deficiency is the most common and affects .50% of the worlds population (4). Previous studies show that iron deficiency increases erythrocyte survival and therefore disproportionately elevates HbA1c concentrations at a given glycemic level (5,6). These were small studies in nondiabetic subjects. There is one similar report in type 1 diabetic patients (7). WHO and ADA have acknowledged this limitation of using HbA1c in the diagnosis of prediabetes and diabetes in nutritionally compromised populations, but not the magnitude of the effect. In the current study, we aimed to investigate the diagnostic performance of HbA1c against a standard OGTT in young adults in a prospective birth cohort (Pune Childrens Study [PCS]) and study the influence of hematological, nutritional, and other factors on HbA1c concentrations. RESEARCH DESIGN AND METHODSdThe study participants were from the PCS (8), which follows children born between 1987 and 1989 in the King Edward Memorial Hospital (KEMH). The study has investigated their growth, glucose tolerance, and cardiovascular risk factors since 1991. In the present round, started in January 2009, we studied these children as 21-year-old young adults. KEMH Research Centres ethics committee approved the study, and all participants gave informed consent. The participants reported to the KEMH Diabetes Unit the evening before the study. Height and weight were measured according to a standard protocol. The next morning, a 75-g OGTT (9) was performed. Blood samples were drawn for the measurement of fasting, 30-min, and 2-h plasma glucose. The fasting sample was also used for the measurement of hematological, biochemical, and nutritional parameters. We started measuring HbA1c concentrations from February 2010, after the ADA recommendations were published (1). In 116 participants, the measurements were performed on the same day as the OGTT; in 127 participants who had already attended the study, a blood sample for only HbA1c was collected at a subsequent home visit. Laboratory analysis Hemoglobin and hematological parameters were measured on a Beckman Coulter analyzer (AcT Diff, Miami, FL). HbA1c was measured using high-performance liquid chromatography (Bio-Rad D-10; Bio-Rad Laboratories, Hercules, CA) calibrated against the National Glycosylated Standardization Program. Coefficients of variations (CVs) were 1.3% at an HbA1c concentration of 5.8% and 1.2% at a concentration of 10.0%. Bio-Rad External Quality Assurances Services results were within 60.1% of the group mean. Blood samples were centrifuged (48C, 2,500g 3 15 min) within 1 h of collection, and plasma was stored at 2808C. Plasma ferritin concentrations were measured using an ELISA (Novatec Immundiagnostica GmbH, Dietzenbach, Germany) on the Victor-2 system (PerkinElmer, Turku, Finland) with a CV of 2%. Plasma glucose was measured by glucose oxidase peroxidase, and creatinine and alanine aminotransferase (ALT) concentrations were measured using standard kits on an analyzer (Hitachi 902, Tokyo, Japan) with a CV ,5% for both. Estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease formula (10). Plasma cobalamin (vitamin B12) and folate were measured by microbiological assay using a colistin sulfate resistant strain of Lactobacillus leichmannii (11,12) and a chloramphenicol-resistant strain of Lactobacillus casei (13,14), respectively. CVs for vitamin B12 and folate measurement were ,8%. Definitions For the OGTT, glycemic status was classified according to WHO criteria (9). The classification of glycemia by HbA1c was performed according to ADA criteria (prediabetes: 5.76.4%; diabetes: $6.5%) (3). Anemia was defined as a hemoglobin concentration ,12 g/dL in females and ,13 g/dL in males (15). Iron, vitamin B12, and folate deficiencies were defined as plasma ferritin, cobalamin, and folate concentrations ,15 ng/mL (15), ,150 pmol/L (16), and ,7 nmol/L, respectively (17). Microcytosis refers to a mean corpuscular volume (MCV) ,80 fL and macrocytosis as MCV .100 fL. Statistical methods Data are presented as mean 6 SD for normally distributed variables and as 50th (25th75th) centiles for skewed variables. Ske (...truncated)