What HbA1c, fasting glucose, OGTT, CGM, kidney and eye tests measure in diabetes, WHO diagnostic thresholds and how often to repeat each test.
Diabetes care runs on numbers — but only if you know what each test measures and when to repeat it. This guide explains the common diabetes tests, the WHO thresholds used for diagnosis, and the regular checks that protect your kidneys, eyes, heart and feet.
| 📌 Key Takeaways | • Diagnosis uses fasting glucose, a 2-hour OGTT, HbA1c or a random glucose with symptoms. | • WHO: fasting ≥126 mg/dL, 2-hour ≥200 mg/dL or HbA1c ≥6.5% is in the diabetes range. | • HbA1c reflects average sugar over about 3 months. | • Kidney (urine albumin, eGFR), eye and foot checks are needed at least yearly. | • Home glucometers guide day-to-day care but are not used for diagnosis. |
WHO thresholds used to diagnose diabetes
| Test | Normal | Intermediate hyperglycaemia | Diabetes | Fasting plasma glucose | Below 110 mg/dL | 110–125 mg/dL (impaired fasting glucose, ICD-11 5A40.0) | 126 mg/dL or above | 2-hour glucose, 75 g OGTT | Below 140 mg/dL | 140–199 mg/dL (impaired glucose tolerance, ICD-11 5A40.1) | 200 mg/dL or above | HbA1c | — | No WHO range (ADA uses 5.7–6.4%) | 6.5% (48 mmol/mol) or above | Random glucose | — | — | 200 mg/dL or above with classic symptoms |
Without symptoms, a single result in the diabetes range is usually confirmed with a repeat test on another day. In pregnancy, different (lower) thresholds apply. You can compare your own results with the free WHO sugar & HbA1c checker.
What your HbA1c means in everyday glucose
HbA1c reflects your average glucose over roughly the past three months. A widely used formula from the ADAG study converts it into an estimated average glucose (eAG): eAG (mg/dL) = 28.7 × HbA1c − 46.7. So an HbA1c of 7% corresponds to an average of about 154 mg/dL, and 8% to about 183 mg/dL. Many adults with diabetes aim for an HbA1c below 7%, but your doctor may set a different personal target.
How often to repeat diabetes tests
• HbA1c: about every 3 months until at target or after a treatment change; about every 6 months when stable.
• Kidney checks (urine albumin-to-creatinine ratio and eGFR): at least once a year.
• Lipid profile: at diagnosis and then as advised, usually yearly.
• Dilated eye examination: yearly, or as your eye specialist advises.
• Foot examination: at least yearly by a clinician, and daily self-checks at home.
• Blood pressure: at every visit.
Every diabetes lab & instrument · what they measure, what they cost, what we use.
Modern diabetes evaluation isn't just an HbA1c — it's a targeted battery of labs and validated psychosocial instruments that triangulate metabolic control, complications risk, self-management ability, and psychological distress.
| Instrument / Test | Measures | Frequency | Format | Evidence base | We use it | HbA1c(Glycated Hemoglobin) | Average glucose over 8-12 weeks · gold standard for diabetes diagnosis (≥6.5%) and monitoring · target <7% most adults | Every 3 months | NABL blood test | Core | FBS / PPBS(Fasting & Post-Prandial Blood Sugar) | Fasting glucose (≥126 = diabetes) · 2-hr post-meal glucose (≥200 = diabetes) · daily monitoring foundation | Weekly-monthly SMBG | Home glucometer or lab | Core | OGTT(Oral Glucose Tolerance Test - 75g) | Diagnostic gold standard for prediabetes and GDM · fasting + 1-hr + 2-hr glucose after 75g glucose load | Screening only | NABL 2-hr sitting test | Prediabetes & GDM diagnosis | Fasting Insulin + C-peptide(with HOMA-IR calculation) | Insulin resistance quantification (HOMA-IR) · C-peptide preserved in T2DM, low in T1DM · MODY/LADA differentiation | At diagnosis, then rarely | NABL blood test | Diagnostic clarity | Urine ACR(Albumin-Creatinine Ratio) | Early diabetic kidney disease · normal <30, microalbuminuria 30-300, macroalbuminuria >300 mg/g | Annual (T2DM from diagnosis · T1DM from 5 yr) | Spot urine | Complications screen | eGFR + Creatinine(estimated Glomerular Filtration Rate) | Kidney function · staged CKD 1-5 · guides medication choice (metformin, SGLT2i, GLP-1RA dosing) | Annual, more if CKD | NABL blood test | Core | Lipid Panel(Total, LDL, HDL, TG, non-HDL) | Cardiovascular risk stratification · LDL targets: <100 general, <70 diabetes+CVD, <55 established ASCVD | Annual (fasting) | NABL blood test | Core | CGM / AGP Report(Continuous Glucose Monitoring / Ambulatory Glucose Profile) | Real-time glucose every 1-5 min · TIR/TBR/TAR metrics · pattern identification · 14-day AGP standard report | 10-14 day sensor cycles | Wearable sensor (arm) | T1DM & complex T2DM | PAID-5 / PAID-20(Problem Areas In Diabetes) | Diabetes-specific emotional distress · cutoff ≥8 (PAID-5) indicates clinically significant distress | At baseline + annually | Self-report | Welch et al. 1997 · widely validated | Distress screen | DDS-17(Diabetes Distress Scale) | Four domains: emotional burden, physician-related, regimen-related, interpersonal · guides support type | Every 6-12 months | Self-report | Polonsky et al. 2005 Diabetes Care | Care experience | SDSCA(Summary of Diabetes Self-Care Activities) | Self-care behaviours across 7 days: diet, activity, glucose monitoring, foot care, medication, smoking | Baseline + intervention studies | Self-report | Toobert, Hampson & Glasgow 2000 | Reversal programme tracking | Clarke Hypoglycemia Awareness(Impaired Awareness of Hypoglycemia) | Detects reduced hypoglycemia awareness · critical for insulin/sulfonylurea users · guides CGM prescription | Annual if on insulin/sulfonylurea | Self-report | Clarke et al. 1995 Diabetes Care | Insulin users | ADA Risk Test(Diabetes Risk Assessment · 7 items) | T2DM risk score based on age, family history, BMI, activity, gestational history, BP · triage screener | Once (self-screen) | Self-report | ADA public health screening tool | Screening | DES-SF(Diabetes Empowerment Scale - Short Form) | Self-efficacy for diabetes self-management · 8 items · predicts adherence and outcomes | Baseline + intervention | Self-report | Anderson et al. 2003 | Reversal / education programmes | PHQ-9 + GAD-7(Depression & Anxiety) | Depression + anxiety comorbidity (~30% depression, ~40% anxiety/distress in diabetes) | Annual · at diagnosis | Self-report | Kroenke 2001 · Spitzer 2006 | Comorbidity | STOP-BANG(OSA Screening) | Obstructive sleep apnea screening (highly prevalent in T2DM: ~50%) | Baseline · at diagnosis | Self-report | Chung et al. 2008 | Comorbid OSA screen |
Complications screens add annual retinography, foot exam, dilated eye exam. Distress screens (PAID-5, DDS-17) added because ~40% of diabetes patients have clinically significant distress. CGM is core for T1DM and complex T2DM.
Need any of these instruments?
HbA1c + FBS + PPBS + lipid + kidney + urine ACR + LFT + TSH + vitamin D — collected at home, reported in 24 hours, reviewed with a diabetologist.
