Diagnosis of Diabetes and Prediabetes
Normal, prediabetes and diabetes on the ADA, WHO and Indian criteria, and why a value at target is not a normal value · v1.1- Say first whether the person already has diabetes, because the same number is read against a diagnostic threshold in one case and against a treatment target in the other.
- Enter whichever results exist: fasting, 2-hour, random, HbA1c. One is enough to start; two are needed to confirm.
- Tick anything that makes the HbA1c unreliable. The tool then reads the glucose values alone and says so.
- The tool gives back one verdict, normal, prediabetes or diabetes, with the criteria that produced it, and a band graphic for each test showing where the value sits and where the treatment target would sit.
- Read the graphic as the point of the tool: the blue target bracket reaches into the amber and red bands, which is why a result at target is not a normal result.
- The type of diabetes. This tool decides whether diabetes is present. Type 1, type 2, LADA, monogenic and pancreatic diabetes are separated by the Diabetes Classification pathway.
- Children under 18, in whom the same thresholds apply but the screening rules and the differential do not.
- Treatment: the choice of drug, the individualised HbA1c target with its rationale, and insulin dosing. Those belong to the outpatient management, inpatient insulin and ketoacidosis modules linked from the result.
- A diagnosis from a capillary glucometer reading or from continuous glucose monitoring. Every threshold here is a venous plasma value from a laboratory, and the ADA states that CGM has insufficient evidence for diagnosis.
- The two-step 50 g and 100 g pregnancy test. It is printed in the Criteria tab for reference and is not used in India.
1. The Question Being Asked
2. The Results enter whichever exist; venous plasma, laboratory measured
1. Diagnostic Thresholds, Non-Pregnant Adults
| Test | Normal | Intermediate | Diabetes | Source |
|---|---|---|---|---|
| Fasting plasma glucose | <100 mg/dL (5.6 mmol/L) on the ADA range; <110 mg/dL (6.1) on the WHO and RSSDI range | Impaired fasting glucose: 100 to 125 mg/dL (ADA); 110 to 125 mg/dL (WHO 1999 and 2006, RSSDI 2022). ICMR 2018 prints both and adjudicates neither | ≥126 mg/dL (7.0 mmol/L) | ADA 2026, WHO 2006, ICMR 2018, RSSDI 2022 |
| 2-hour plasma glucose, 75 g OGTT | <140 mg/dL (7.8 mmol/L) | Impaired glucose tolerance: 140 to 199 mg/dL (7.8 to 11.0 mmol/L) | ≥200 mg/dL (11.1 mmol/L) | All four agree |
| HbA1c | <5.7 per cent (39 mmol/mol) on the ADA range. WHO defines no intermediate range | 5.7 to 6.4 per cent (39 to 47 mmol/mol), ADA and RSSDI | ≥6.5 per cent (48 mmol/mol), NGSP-certified assay | International Expert Committee 2009, ADA 2010 onward, WHO 2011, ICMR 2018, RSSDI 2022 |
| Random plasma glucose | Not a screening threshold | Not defined. A value of 140 to 199 mg/dL calls for a fasting test or an HbA1c | ≥200 mg/dL (11.1 mmol/L) with classic symptoms or a hyperglycaemic crisis | ADA 2026, ICMR 2018 |
| 1-hour plasma glucose, 75 g OGTT | <155 mg/dL (8.6 mmol/L) | ≥155 mg/dL: intermediate hyperglycaemia | ≥209 mg/dL (11.6 mmol/L), to be confirmed by repeat | IDF position statement 2024 only. Not adopted by ADA 2026, WHO, ICMR or RSSDI |
2. Thresholds in Pregnancy
| Test | Gestational diabetes | Notes | Source |
|---|---|---|---|
| DIPSI: 75 g glucose, irrespective of the last meal, 2-hour plasma glucose | ≥140 mg/dL (7.8 mmol/L) | 120 to 139 mg/dL is gestational glucose intolerance and is followed up. The national test at the first contact and at 24 to 28 weeks. Against IADPSG its sensitivity was 22.6 per cent in 1,031 women | MoHFW 2018, DIPSI |
| IADPSG one-step: fasting 75 g OGTT | Fasting ≥92 mg/dL (5.1), 1-hour ≥180 (10.0), 2-hour ≥153 (8.5). One value diagnoses | Derived from HAPO at 1.75 times the odds of an adverse outcome. Raises the diagnosed prevalence roughly one- to threefold | IADPSG 2010, WHO 2013, ADA 2026 |
| Two-step: 50 g screen then 100 g OGTT | Screen positive at 130, 135 or 140 mg/dL at 1 hour; then two of fasting 95, 1-hour 180, 2-hour 155, 3-hour 140 (Carpenter-Coustan) | The United States alternative. Not used in India; printed for reference only | ADA 2026 Table 2.8 |
| Overt diabetes in pregnancy | The non-pregnant criteria: fasting ≥126, 2-hour ≥200, random ≥200 with symptoms, and HbA1c ≥6.5 per cent before 15 weeks (ADA 2.31a). From 15 weeks the HbA1c is set aside and plasma glucose decides (ADA 2.4) | Classified as diabetes complicating pregnancy, not GDM, whenever it is found. Reclassify every GDM at 4 to 12 weeks post partum (ADA), 6 weeks under the national programme, using the non-pregnant criteria | ADA 2026, MoHFW 2018 |
3. Treatment Targets, Which Are Not Normal Values
| Population | HbA1c | Fasting or pre-meal | After meals | Source |
|---|---|---|---|---|
| Many non-pregnant adults with diabetes | <7.0 per cent (53 mmol/mol); <6.5 may be appropriate where it can be reached without hypoglycaemia | 80 to 130 mg/dL (4.4 to 7.2 mmol/L) | <180 mg/dL (10.0 mmol/L) at the peak, 1 to 2 hours after the start of the meal | ADA 2026, section 6 |
| Continuous glucose monitoring | Time in range 70 to 180 mg/dL above 70 per cent; below 70 mg/dL under 4 per cent; below 54 under 1 per cent | A time in range of 70 per cent corresponds to an HbA1c near 7 per cent | ADA 2026, section 6 | |
| ICMR 2018 | Ideal <7 per cent; satisfactory 7 to under 8 | Ideal 80 to 110 mg/dL; satisfactory 111 to 125 | 2-hour ideal 120 to 140 mg/dL; satisfactory 141 to 180 | ICMR 2018, section 4.1 |
| RSSDI 2022 | <7.0 per cent | 160 mg/dL, as long as hypoglycaemia is avoided | RSSDI 2022 | |
| Older adult, generally healthy | <7.0 to 7.5 per cent | 80 to 130 mg/dL | Bedtime 80 to 180 mg/dL | ADA 2026, section 13 |
| Older adult, complex or intermediate health | <8.0 per cent (64 mmol/mol) | 90 to 150 mg/dL | Bedtime 100 to 180 mg/dL | ADA 2026, section 13 |
| Older adult, very complex or poor health | Do not rely on HbA1c; avoid hypoglycaemia and symptomatic hyperglycaemia | 100 to 180 mg/dL | Bedtime 110 to 200 mg/dL | ADA 2026, section 13 |
| Pregnancy, any diabetes | <6 per cent (42 mmol/mol) if achievable without hypoglycaemia; relaxed to <7 if necessary | <95 mg/dL (5.3 mmol/L) | 1-hour <140 mg/dL or 2-hour <120 mg/dL | ADA 2026, section 15 |
4. When the HbA1c Cannot Be Used
| Condition | Direction of error | What to do |
|---|---|---|
| Iron deficiency anaemia, B12 or folate deficiency | Reduced red cell turnover: HbA1c reads falsely high | Diagnose on plasma glucose. In India the NFHS-5 anaemia prevalence of 57 per cent among women makes this the commonest reason |
| Haemolysis, blood loss, transfusion, erythropoietin, pregnancy from 15 weeks | Increased turnover or dilution: HbA1c reads falsely low | Diagnose on plasma glucose. Before 15 weeks the ADA applies the standard criteria, HbA1c included; from 15 weeks use the pregnancy thresholds |
| Haemoglobin variant or trait: HbS, HbC, HbE, HbD, thalassaemia | Assay dependent, either direction | Use an assay without interference for that variant (ngsp.org/interf.asp), or diagnose on glucose. RSSDI: fructosamine as a surrogate |
| Chronic kidney disease stage 4 or 5, dialysis | Falsely low, from shortened red cell survival and erythropoietin | Diagnose on glucose |
| HIV on antiretroviral treatment; G6PD deficiency | Falsely low | Diagnose on glucose (ADA 2026 recommendation 2.4) |
| Point-of-care device | Imprecision | Acceptable for diagnosis only when the device is certified for diagnosis and run in a certified laboratory |
5. How the Thresholds Came to Sit Where They Do
| Year | Document | What moved |
|---|---|---|
| 1979 | National Diabetes Data Group | Fasting 140 mg/dL, 2-hour 200 mg/dL, impaired glucose tolerance defined |
| 1980 and 1985 | WHO Expert Committee and Study Group | Adopted the same frame internationally |
| 1997 | ADA Expert Committee | Fasting lowered to 126 mg/dL, chosen because that is where the prevalence of retinopathy rises and where it matches the 2-hour 200; impaired fasting glucose introduced at 110 to 125 |
| 1999 | WHO | Adopted 126 and 110 to 125; a single value never diagnoses an asymptomatic person |
| 2003 | ADA follow-up report | Impaired fasting glucose lowered to 100. WHO did not follow, in 2006 or since |
| 2009 and 2010 | International Expert Committee; ADA | HbA1c 6.5 per cent for diagnosis; the ADA added 5.7 to 6.4 |
| 2011 | WHO; DETECT-2 | WHO accepted 6.5 with stringent quality assurance and no intermediate range. DETECT-2 pooled 44,623 people and found the retinopathy threshold at a fasting glucose of 6.5 mmol/L and an HbA1c of 6.5 per cent |
| 2024 | International Diabetes Federation | Proposed the 1-hour value, 155 and 209 mg/dL. Not adopted by ADA 2026 or by any Indian document |
1. The Difference Between a Normal Value and a Target
A diagnostic threshold is set where the risk of retinopathy begins to rise in a population without diabetes. A treatment target is set where the risk of hypoglycaemia and treatment burden begins to outweigh the benefit of lower glucose in a person who already has the disease. They answer different questions and were never intended to coincide.
- An HbA1c of 6.2 per cent is prediabetes-range in a person without diabetes and at target in a person with it.
- A fasting glucose of 120 mg/dL is impaired fasting glucose and is also inside the 80 to 130 target.
- A fasting glucose of 93 mg/dL in pregnancy is gestational diabetes on IADPSG and is inside the treatment target of below 95.
- A person with diabetes whose values fall into the non-diabetic range on treatment has reached target. The diagnosis stands, and remission is a separate, defined state.
2. The Two Definitions of Impaired Fasting Glucose
The ADA lowered the floor from 110 to 100 mg/dL in 2003 to make the fasting category as sensitive as impaired glucose tolerance. WHO kept 110 in 2006 because the lower floor more than doubles the number of people labelled, without evidence that the added group benefits from intervention. RSSDI 2022 follows WHO; ICMR 2018 prints both.
3. What the Indian Prevalence Figures Mean at the Bedside
- ICMR-INDIAB 2023, 113,043 adults across every state: diabetes 11.4 per cent, prediabetes 15.3 per cent, both by WHO criteria. In many states with a lower human development index there is more prediabetes than diabetes.
- CURES 10-year follow-up, Chennai: 58.9 per cent of people with prediabetes converted to diabetes, and 19.4 per cent of those with normal glucose tolerance converted directly to diabetes within a decade. Among the highest conversion rates recorded anywhere.
- IDPP-1, 531 Indian adults with impaired glucose tolerance: 55 per cent of the control group had diabetes within 3 years. Lifestyle advice reduced that by 28.5 per cent and metformin by 26.4 per cent; combining them added nothing. Number needed to treat 6.4.
- The ADA screens from age 35, or at a body mass index of 23 with a risk factor in people of Asian ancestry. ICMR 2018 screens everyone above 30.
4. The Three Tests Do Not Find the Same People
In the CURES cohort, the prevalence of diabetes in 2,188 adults was 6.1 per cent by fasting glucose, 10.1 per cent by the 2-hour value and 12.8 per cent by HbA1c. Only 121 of the 281 diagnosed met all three criteria. The ADA records that the 2-hour value diagnoses more people than either of the others, and that the trials preventing progression were done in people with impaired glucose tolerance, not in isolated impaired fasting glucose or HbA1c-defined prediabetes.
- The same Chennai laboratory found HbA1c cut points of 6.1 per cent against the 2-hour criterion and 6.4 against the fasting one, and 5.6 for the intermediate group at under 70 per cent accuracy. These are printed as context. The tool applies the international 6.5 and 5.7, as ICMR and RSSDI do.
- A fasting glucose alone misses roughly a third of Indian diabetes. Where the fasting value is in the impaired range, the 2-hour test is the one that changes management.
5. Why HbA1c Fails More Often in India
HbA1c is a weighted average over the life of the red cell, so anything that shortens or lengthens that life moves the number without any change in glucose.
- Iron deficiency raises it. NFHS-5 found anaemia in 57 per cent of women aged 15 to 49.
- Haemoglobin variants are carried by 3 to 4 per cent of the population, more in the north-east for HbE and in the tribal belts for HbS, and interfere in an assay-dependent direction.
- Pregnancy from the second trimester, transfusion, haemolysis, dialysis, erythropoietin and HIV treatment lower it. Before 15 weeks the ADA still applies the standard criteria, and an HbA1c of 5.9 to 6.4 per cent there marks early abnormal glucose metabolism (ADA 2.31b), a risk category rather than a diagnosis.
- The ADA recommendation is plasma glucose in all of these. A haemoglobin variant is often first suspected from an HbA1c that does not fit the glucose, which is why the ADA asks for evaluation whenever the two disagree consistently.
6. The Confirmation Rule in Practice
Two abnormal results from different tests on the same sample also confirm. A fasting glucose of 140 and an HbA1c of 6.8 per cent from one venepuncture is a diagnosis, and the patient does not need to return fasting.
7. Diagnosis in Pregnancy and the National Test
- DIPSI is the national test because it needs no fasting and one visit. Its threshold of 140 mg/dL was retained by the 2018 national guideline, with 120 to 139 followed up as gestational glucose intolerance.
- Against IADPSG it is insensitive: 22.6 per cent in 1,031 women in one Chennai series. A negative DIPSI in a woman with risk factors does not settle the question, and a fasting 75 g test with IADPSG thresholds is the better test where it is feasible.
- Every woman with gestational diabetes is reclassified after delivery with the non-pregnant criteria. The programme says 6 weeks; the ADA says 4 to 12 weeks, then every 1 to 3 years for life. The Pregnancy Timeline carries the schedule.
8. What Follows a New Diagnosis
The diagnosis is the beginning of a workup, not the end of one. The tool links to each step on the branch where it is wanted:
- Which type: the Diabetes Classification pathway, particularly for a lean adult, a young adult, or anyone presenting with ketosis.
- Complications present at diagnosis: albuminuria with the UACR calculator, kidney function with Renal Staging, the fundus, and the feet.
- Cardiovascular risk with the CVD Risk Master and the lipid pattern with the Atherogenic Profiler; fatty liver with FIB-4 and Elastography.
- The individualised target from the HbA1c Target tool, and treatment in the Outpatient Diabetes Management pathway; insulin on the ward from Inpatient Insulin.
Abbreviations
ACOG (American College of Obstetricians and Gynecologists) · ADA (American Diabetes Association) · B12 (Vitamin B12) · BMI (Body Mass Index) · CGM (Continuous Glucose Monitoring) · CURES (Chennai Urban Rural Epidemiology Study) · CVD (Cardiovascular Disease) · DCCT (Diabetes Control and Complications Trial) · DIPSI (Diabetes in Pregnancy Study Group India) · DKA (Diabetic Ketoacidosis) · FIB-4 (Fibrosis-4 Index) · G6PD (Glucose-6-Phosphate Dehydrogenase) · GDM (Gestational Diabetes Mellitus) · HAPO (Hyperglycemia and Adverse Pregnancy Outcome Study) · HbA1c (Glycated Haemoglobin) · HbC (Haemoglobin C) · HbD (Haemoglobin D) · HbE (Haemoglobin E) · HbS (Haemoglobin S) · HHS (Hyperglycaemic Hyperosmolar State) · HIV (Human Immunodeficiency Virus) · IADPSG (International Association of Diabetes and Pregnancy Study Groups) · ICMR (Indian Council of Medical Research) · ICMR-INDIAB (Indian Council of Medical Research India Diabetes Study) · IDF (International Diabetes Federation) · IDPP (Indian Diabetes Prevention Programme) · IFCC (International Federation of Clinical Chemistry and Laboratory Medicine) · IFG (Impaired Fasting Glucose) · IGT (Impaired Glucose Tolerance) · LADA (Latent Autoimmune Diabetes in Adults) · MoHFW (Ministry of Health and Family Welfare) · NDDG (National Diabetes Data Group) · NFHS (National Family Health Survey) · NGSP (National Glycohemoglobin Standardization Program) · OGTT (Oral Glucose Tolerance Test) · RSSDI (Research Society for the Study of Diabetes in India) · UACR (Urine Albumin to Creatinine Ratio) · WHO (World Health Organization)References
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- American Diabetes Association Professional Practice Committee. 13. Older adults: Standards of Care in Diabetes-2026. Diabetes Care 2026;49(Suppl 1):S277-S296.
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How to Cite This Tool
AMA Style:Umakanth S. Diagnosis of Diabetes and Prediabetes. Version 1.1. MEDiscuss Clinical Decision Support System. Published 2026. Accessed . https://mediscuss.org/cdss/diabetes-diagnosis
Vancouver Style:Umakanth S. Diagnosis of Diabetes and Prediabetes [Internet]. Version 1.1. MEDiscuss.org; 2026 [cited ]. Available from: https://mediscuss.org/cdss/diabetes-diagnosis
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