Endocrine
Type 2 diabetes: diagnosis, first-line therapy and what to screen for
The diagnostic cutoffs, why metformin is still the usual start, when to add an SGLT2 inhibitor or GLP-1 receptor agonist, and the yearly checks.
10 min read·core·
Reviewed by a licensed nurse · 22 October 2026
Diagnostic cutoffs
| Test | Prediabetes | Diabetes |
|---|---|---|
| A1c | 5.7 to 6.4% | 6.5% or higher |
| Fasting glucose | 100 to 125 mg/dL | 126 mg/dL or higher |
| 2-hour OGTT | 140 to 199 mg/dL | 200 mg/dL or higher |
In the absence of unequivocal hyperglycemia, diagnosis normally requires two abnormal results, from the same sample or two separate tests.
Choosing treatment
Lifestyle change is always part of treatment, and metformin remains the usual first pharmacologic choice because it is effective, inexpensive, weight neutral and does not cause hypoglycemia on its own.
The modern twist is that the drug choice is now driven by the patient's comorbidities, not only by the A1c. In a patient with atherosclerotic cardiovascular disease, heart failure or chronic kidney disease, a GLP-1 receptor agonist or an SGLT2 inhibitor with proven benefit is recommended in addition to, or in some cases instead of, metformin.
A way to reason through a drug question
- 01
What does the patient have besides diabetes?
Atherosclerotic cardiovascular disease: GLP-1 receptor agonist or SGLT2 inhibitor with proven cardiovascular benefit. Heart failure: SGLT2 inhibitor. CKD: SGLT2 inhibitor, with a GLP-1 receptor agonist as an option.
- 02
Is there a reason not to use metformin?
eGFR below 30 is a contraindication. Starting at an eGFR of 30 to 45 is not recommended, and the dose is reduced if it falls there on treatment. Hold around iodinated contrast in at-risk patients and in acute illness with dehydration or hypoxia.
- 03
Is weight or hypoglycemia the main concern?
GLP-1 receptor agonists and SGLT2 inhibitors lower weight and rarely cause hypoglycemia alone. Sulfonylureas and insulin carry hypoglycemia risk and weight gain.
- 04
Check the adverse-effect trap
SGLT2 inhibitors: genital mycotic infections, volume depletion, euglycemic ketoacidosis. GLP-1 receptor agonists: nausea, and a contraindication with a personal or family history of medullary thyroid carcinoma or MEN2.
Yearly and routine checks
- ·Dilated retinal examination (at diagnosis for type 2, then at intervals set by findings)
- ·Comprehensive foot examination, including monofilament testing
- ·Urine albumin-to-creatinine ratio and eGFR
- ·Blood pressure at every visit, with lipid management and statin therapy by age and risk
- ·Vaccinations, including influenza, pneumococcal and hepatitis B as indicated
Check yourself
Did it stick?
1. A patient has an A1c of 6.8% on a single test and no symptoms. What is the best next step?
2. A patient with type 2 diabetes and heart failure with reduced ejection fraction needs additional therapy. Which class has proven benefit for both conditions?
3. At which eGFR is metformin contraindicated?
Sources
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Educational content for exam preparation. It is not clinical guidance and does not replace your facility's policies, current professional guidelines or the advice of a qualified clinician.