12.1 Diabetes Diagnosis and Monitoring
Key Takeaways
- ADA 2026 diabetes: A1c ≥6.5%, FPG ≥126 mg/dL, 2-hour 75-g OGTT ≥200 mg/dL, or random ≥200 mg/dL plus classic symptoms — confirm unless DKA/HHS or unequivocal hyperglycemia.
- Prediabetes is A1c 5.7–6.4%, FPG 100–125 mg/dL, or 2-hour OGTT 140–199 mg/dL; USPSTF screens adults 35–70 with overweight or obesity, then about every 3 years if normal and at least annually if prediabetes.
- Type 1 needs insulin from the start; LADA looks like type 2 then fails orals — check GAD65 in a leaner adult with other autoimmune disease; GDM is first recognized in pregnancy and needs a postpartum OGTT.
- A1c about every 3 months when changing therapy or not at goal, about every 6 months when stable; target near 7% for many nonpregnant adults, looser if frail or hypoglycemia-prone.
- DKA and HHS leave by ambulance. Anyone on insulin or a sulfonylurea needs a written 15-15 hypoglycemia plan and glucagon if level-2 or level-3 risk exists.
The current FNP-BC Test Content Outline lists endocrine among the 13 body systems and endocrine agents among the official drug classes. Domain II Diagnosis asks you to separate type 1, type 2, latent autoimmune diabetes of adults (LADA), and gestational diabetes and to apply ADA Standards of Care 2026 thresholds — not a remembered 2018 shortcut. Domain IV Implementation and Domain V Evaluation ask whether you order the right surveillance labs, recognize DKA or HHS before the patient walks out, and write a hypoglycemia plan that a household contact can actually follow.
ADA 2026 diagnostic criteria
Diabetes is present when any one of these laboratory criteria is met:
| Test | Diabetes | Prediabetes | Practical note |
|---|---|---|---|
| A1c | ≥6.5% | 5.7–6.4% | Use an NGSP-certified laboratory method. Do not diagnose by A1c in pregnancy, a known hemoglobinopathy, recent transfusion, or marked anemia — use plasma glucose. |
| Fasting plasma glucose (FPG) | ≥126 mg/dL | 100–125 mg/dL (impaired fasting glucose) | Fast at least 8 hours. |
| 2-hour 75-g OGTT | ≥200 mg/dL | 140–199 mg/dL (impaired glucose tolerance) | Timed laboratory draw after a 75-g load. |
| Random plasma glucose | ≥200 mg/dL plus classic symptoms | — | Polyuria, polydipsia, and unexplained weight loss. |
Confirm unless crisis. In the absence of unequivocal hyperglycemia or a hyperglycemic crisis (DKA or HHS), diagnosis requires a second confirmatory test — the same test on a different day, or a different diagnostic test. If A1c is 6.7% and FPG is 118 mg/dL, you have one diagnostic result and one prediabetes result: repeat the test that was diagnostic. Do not average discordant tests into a maybe. Two different tests that are both diagnostic on the same day can establish the diagnosis. A hallway glucometer value is not a diagnostic plasma glucose unless you also have laboratory confirmation or the patient is in crisis.
Exam trap. A random glucose of 208 mg/dL in an asymptomatic adult is not diabetes until you confirm with A1c, FPG, or OGTT. A random 208 mg/dL plus two weeks of polyuria, polydipsia, and an 8-lb weight loss is diagnostic and does not need a polite delay.
Who to screen and how often
USPSTF recommends screening adults aged 35–70 years who have overweight or obesity (Grade B). Screen earlier when additional risk is high: a first-degree relative with diabetes, prior gestational diabetes, PCOS, hypertension, dyslipidemia, high-risk race or ethnicity, or acanthosis nigricans. ADA also supports screening all adults beginning at age 35 and screening youth who have overweight plus a risk factor. If the result is normal, repeat about every 3 years. If the result is prediabetes, repeat at least annually and start intensive lifestyle change (about 7% weight loss and 150 minutes of activity per week). Metformin for prevention is reasonable in selected high-risk adults (history of GDM, BMI ≥35, younger than 60) — that is prevention of type 2, not a diagnosis of type 2.
Anyone with a history of GDM needs lifelong screening at least every 3 years, starting with a postpartum 4–12 week OGTT. Do not close the obstetric chart and forget the pancreas. Children and adolescents with overweight plus a risk factor (family history, maternal diabetes or GDM, signs of insulin resistance) get screened. Type 2 is no longer an adult-only disease. Type 1 can appear at any age; do not refuse insulin because the birthday is 41.
Type 1 versus type 2 versus LADA versus gestational
| Feature | Type 1 | Type 2 | LADA | Gestational |
|---|---|---|---|---|
| Onset | Often abrupt; any age, classically youth | Gradual; usually adult | Adult; looks like type 2 at first | First recognized in pregnancy |
| Habitus | Often lean; any BMI possible | Often overweight or obesity | Often leaner than typical type 2 | Any; risk rises with BMI |
| Ketosis | Common; insulin required from the start | Uncommon except ketosis-prone type 2 or SGLT2-related | Delayed; insulin eventually | Unusual — hospitalize if present |
| Autoantibodies | GAD65, IA-2, ZnT8, IAA often positive | Usually negative | GAD65 often positive | Negative (if positive, think preexisting type 1) |
| C-peptide | Low or undetectable | Present | Declines over months to years | Present |
| Immediate insulin | Yes | Not always | Not always on day 1 | If diet fails; some obstetric plans use metformin |
Type 1 is autoimmune beta-cell destruction. Do not withhold insulin because the patient is 42 or the BMI is 29. Type 2 is insulin resistance plus a relative insulin secretory defect. Family history, central obesity, and a gradual course support type 2; none of those findings rules out LADA. LADA presents like type 2, often in a leaner adult with other autoimmune disease, then progresses to insulin dependence. If oral agents fail quickly in a thin 38-year-old, order GAD65 rather than stacking a fourth noninsulin drug. Gestational diabetes is glucose intolerance first recognized in pregnancy. Screen at 24–28 weeks with the one-step 75-g or two-step 50-g then 100-g protocol your obstetric partners use. Screen early in pregnancy if risk is high; an early diagnostic result may be preexisting type 2, not GDM. After delivery, GDM is not cured forever.
Vignette. A 41-year-old with BMI 24, Hashimoto thyroiditis, and an A1c of 7.4% is not automatically type 2. Check antibodies. Do not promise that metformin alone will last a decade.
A1c targets and the monitoring clock
Individualize the target. For many nonpregnant adults, an A1c around 7% is the default. Tighter (near 6.5%) is reasonable if it can be reached without hypoglycemia in a motivated adult with long life expectancy. Looser (under 8%, or even higher) is correct in frailty, limited life expectancy, hypoglycemia unawareness, advanced vascular disease, or when the regimen includes insulin or a sulfonylurea and a low glucose means a fall or an arrhythmia. Do not chase 6.5% in an 86-year-old on glyburide.
When to draw A1c. When you are changing therapy or the patient is not at goal, about every 3 months. When the regimen and the A1c are stable at goal, about every 6 months. A1c reflects roughly 2–3 months of glycemia; repeating it in 2 weeks to see if the new metformin worked is not Evaluation — it is impatience.
CGM, conceptually. Continuous glucose monitoring is standard in type 1 and is increasingly used in type 2 treated with insulin. Time-in-range (commonly 70–180 mg/dL) and time-below-range complement A1c. You do not need a device brand on the exam. You do need to know that a good A1c can hide dangerous lows, and that CGM is how you see them.
Home capillary glucose. Anyone on insulin or a sulfonylurea needs a home-glucose plan and a written hypoglycemia plan. People on metformin, an SGLT2 inhibitor, or a GLP-1 receptor agonist alone, without a secretagogue, have a low hypoglycemia risk and do not need four-times-daily fingersticks for safety — they still need a sick-day plan and a way to check if they become ill.
Complication screening you actually order
At diagnosis of type 2 (and after about 5 years of type 1, then ongoing):
| Screen | Interval | Why it changes the plan |
|---|---|---|
| Urine albumin–creatinine ratio (UACR) | At diagnosis and at least annually | Stages CKD; ACE/ARB and SGLT2 decisions |
| eGFR | At diagnosis and at least annually | Metformin eligibility, dosing, CKD stage |
| Dilated retinal exam | Type 2 at diagnosis; type 1 after ~5 years; at least annually (can extend if repeatedly normal) | Treatable retinopathy before vision is gone |
| Comprehensive foot exam | At least annually; every visit if neuropathy, deformity, or prior ulcer | Ulcer and amputation |
| Lipids | At diagnosis and periodically | Most adults 40–75 with diabetes meet a statin indication |
| Blood pressure | Every visit | ACE/ARB if albuminuria; usual hypertension targets |
Also address dental health, depression and diabetes distress, indicated vaccines, and tobacco. A monofilament exam is not optional decoration. Document pulses, skin, deformity, and sensation. Refer ulcers the same week, not after the next A1c.
DKA and HHS leave by ambulance
DKA is anion-gap metabolic acidosis plus ketones, usually with hyperglycemia. Nausea, vomiting, abdominal pain, Kussmaul respirations, fruity breath, and volume depletion are the office clues. DKA can be euglycemic on an SGLT2 inhibitor — do not wait for a glucose of 400. HHS is extreme hyperglycemia (often >600 mg/dL), profound dehydration, effective hyperosmolarity, little or no ketoacidosis, and altered mentation, typically in an older adult with type 2 who could not keep water down. Both are emergency-department diseases. Do not give a hallway correction of subcutaneous insulin and send the patient home. Do not wait for tomorrow's A1c. Call EMS. Send the medication list, especially SGLT2 inhibitors and insulin.
Write the hypoglycemia plan
Level 1: glucose <70 mg/dL. Treat with 15 g of fast carbohydrate, recheck in 15 minutes, repeat if still low, then a snack if the next meal is not imminent (the 15-15 rule). Level 2: <54 mg/dL — serious; review the regimen the same week. Level 3: severe — the person needs help from someone else. Prescribe glucagon (intranasal or autoinjector) for anyone at risk of level 2 or 3 and teach a household contact. Counsel driving, occupational safety, and hypoglycemia unawareness (no adrenergic warning; often needs a temporarily higher glucose target). Recurring lows on a sulfonylurea or insulin are an Implementation miss if you only say eat more and do not reduce the dose.
Sick-day rules. Continue basal insulin in type 1 — never stop it. Check glucose more often. Check ketones if the patient has type 1 or takes an SGLT2 inhibitor and is unwell. Hold SGLT2 inhibitors when oral intake is poor or before major surgery (euglycemic DKA). Hold metformin during dehydrating illness or around iodinated contrast when eGFR is reduced. Send to the ED for persistent vomiting, ketones, or glucose that will not come down.
An asymptomatic 48-year-old with BMI 31 has an A1c of 6.7% and a fasting plasma glucose of 118 mg/dL drawn the same morning. Using ADA 2026 criteria, what is the correct next diagnostic step?
A lean 39-year-old with Hashimoto thyroiditis was labeled type 2 diabetes 18 months ago. Metformin then a DPP-4 inhibitor failed, and the A1c is now 8.9% with no weight gain. Which test best distinguishes LADA from ordinary type 2 diabetes?
An 78-year-old with type 2 diabetes is brought in by family for two days of poor intake, confusion, and dry mucous membranes. Fingerstick glucose is 640 mg/dL. There is no Kussmaul breathing. Which FNP action is correct?
A 62-year-old with type 2 diabetes just started basal insulin. A1c last week was 9.1%. Which monitoring plan matches usual primary-care practice?