High A1c: what the levels mean, causes, how to confirm and what to check next

• age 18+: 4 – 5.6 %

5.7–6.4% indicates prediabetes; 6.5% or higher on two tests suggests diabetes. Even small reductions improve long-term risk.

Full reference table, citations and testing options: Hemoglobin A1c biomarker page.

1. Prediabetes and type 2 diabetes — insulin resistance with excess weight, inactivity, a family history, PCOS, past gestational diabetes; the common cause
2. Type 1 diabetes, latent autoimmune diabetes in adults (LADA) and the rarer forms — monogenic (MODY), pancreatic disease or surgery, hemochromatosis, cystic fibrosis
3. Medications that raise glucose — glucocorticoids, some antipsychotics (olanzapine, clozapine), thiazides, beta-blockers, statins (slightly), niacin, tacrolimus and cyclosporine, HIV protease inhibitors
4. Endocrine conditions — Cushing's syndrome, acromegaly, hyperthyroidism, glucagonoma
5. Falsely high A1c with normal glucose — iron deficiency anemia, vitamin B12 or folate deficiency, asplenia (red cells live longer), chronic kidney disease (carbamylated hemoglobin), alcohol excess, high-dose aspirin, some hemoglobin variants on some assays
6. Late pregnancy is NOT a cause — A1c runs lower in pregnancy; gestational diabetes is diagnosed by glucose tolerance testing

• Often none in the prediabetes range and early type 2 diabetes — the test is how most people find out
• Thirst, frequent urination, blurred vision, fatigue and unexplained weight loss as glucose rises
• Slow-healing sores, recurrent yeast or skin infections, tingling or numbness in the feet
• Nausea, vomiting, abdominal pain and deep rapid breathing with a very high glucose — ketoacidosis, an emergency

• Confirm the diagnosis: a second A1c, or a fasting glucose (126 mg/dL or more) or 2-hour glucose on a tolerance test (200 or more) — two abnormal results are needed unless glucose is unequivocally high with symptoms
• Check the confounders when the A1c does not fit the glucose readings: a CBC with ferritin, B12 and folate; eGFR; and ask the lab about hemoglobin variants — fructosamine or a continuous glucose monitor's glucose management indicator are the alternatives
• A metabolic baseline: lipid panel, creatinine and eGFR, a urine albumin-to-creatinine ratio, liver enzymes and blood pressure — the complications and companions of diabetes are managed from day one
• In a lean adult, a child or anyone with rapid weight loss: GAD and other islet antibodies and a C-peptide to distinguish type 1 and LADA from type 2
• Retest every 3 months while treatment or habits are changing (the test cannot move faster than red cells turn over), every 6 months once stable
• Diabetes is managed with your clinician — the targets (usually below 7%, individualized from 6.5 to 8) and the choice of lifestyle program and medication depend on age, weight, kidney function and cardiovascular risk

Follow-up tests available at TestWell: CBC with Differential Test ($17.99), Lipid Panel ($19.99), Ferritin Test ($21.99), Folate Test (Vitamin B9) ($21.99), C-Peptide Test ($29.99), Colon Cancer Screening Test (FIT) ($59.99).

The American Diabetes Association recommends an A1c at least twice a year when you're meeting goals with stable control, and every 3 months after a therapy change or when you're not at goal. With prediabetes, a yearly A1c is the usual cadence. Because it reflects a ~3-month average, retesting sooner than 8–12 weeks rarely shows a real change.