Key values on the report

How to read it

• Category: The usual bands are <5.7% normal, 5.7-6.4% prediabetes and ≥6.5% diabetes. At 14.1% this is far above the diagnostic threshold.
• What it reflects: HbA1c shows average glycemia over the previous 2-3 months. Harrison's notes that it "reflects average glycemic control over the previous 2-3 months" - Harrison's Principles of Internal Medicine 22E, Monitoring the Level of Glycemic Control. The eAG of about 357 mg/dL fits this.
• Result is likely reliable: The chromatogram has a clean HbA1c peak. There is no variant hemoglobin peak (HbS, C, D or E) and HbF is not raised. Variants and high HbF can distort HbA1c, so this lowers the chance of an artefact. The report doesn't give anemia status. Iron deficiency, hemolysis, recent transfusion, CKD and B12 deficiency can also shift HbA1c, so check CBC and clinical context.
• Cross-check the math: eAG = 28.7 × 14.1 − 46.7 ≈ 358 mg/dL. IFCC = (14.1 − 2.15) × 10.93 ≈ 130.6. Both match the report.

Clinical implications

• Target in older adults: Harrison's says the goal depends on health status. It may be <7.0% with robust cognition and few comorbidities, and looser with impaired cognition or in a care facility - Harrison's, Establishment of Target Level of Glycemic Control. Katzung says "for the elderly, frail patient an HbA1c close to 8% may be appropriate" - Katzung's Basic and Clinical Pharmacology, 16th Ed, Glycemic Targets. Either way, 14.1% is far above any reasonable target.
• Urgent assessment is needed. An HbA1c this high calls for a same-day review for:
  • Symptoms of hyperglycemia: polyuria, polydipsia, weight loss, fatigue, blurred vision.
  • Dehydration, confusion or drowsiness, which may suggest a hyperosmolar hyperglycemic state.
  • Ketones if she is unwell or losing weight, as insulin deficiency is possible.
  • Infection or another precipitant, and medication adherence.
• Treatment: In an older adult with HbA1c well above 10%, clinicians usually start or intensify insulin. They also review current drugs, renal function (eGFR) and hypoglycemia risk before choosing agents. Dose and drug choice need her treating doctor.
• Complication screening: Check kidney function and urine albumin, a dilated eye exam, a foot exam, lipids, blood pressure and cardiovascular risk. Also check for a cognitive or functional decline that could affect self-management.
• Follow-up: Repeat HbA1c in about 3 months after therapy changes. Home glucose monitoring or a CGM helps in the meantime. Lower the glucose steadily, not abruptly, since a rapid fall can worsen retinopathy.

Recent evidence check

Limits

Possible causes

• It has two parts: tissue resistance to insulin, and a relative lack of insulin from the pancreas.
• Katzung describes it as "tissue resistance to the action of insulin combined with a relative deficiency in insulin secretion". Some people have more resistance and some have more beta cell failure - Katzung's Basic and Clinical Pharmacology, 16th Ed, Type 2 Diabetes Mellitus.
• Tietz adds that a relative insulin deficiency occurs early in the disease and an absolute deficiency late in it - Tietz Textbook of Laboratory Medicine, 7th Ed, Pathogenesis of Type 2 Diabetes Mellitus.
• Years of untreated or undertreated diabetes lead to beta cell exhaustion. Prolonged high glucose also suppresses insulin secretion and worsens resistance (glucotoxicity). An HbA1c of 14% can therefore mean "insulin resistance plus a pancreas that can no longer keep up". This is a common reason these patients end up needing insulin.

• Type 1 diabetes or latent autoimmune diabetes of adults (LADA) is less common at 76 but possible. It involves autoimmune beta cell destruction - Henry's Clinical Diagnosis and Management by Laboratory Methods, Classification of Diabetes Mellitus.
• Pancreatic disease, such as chronic pancreatitis or a pancreatectomy, can also cause it.

• Robbins notes that new-onset diabetes in older patients may be the first sign of an occult pancreatic cancer, and that abnormal glucose tolerance is present in up to half of pancreatic cancer patients up to 2 years before clinical signs - Robbins, Cotran & Kumar Pathologic Basis of Disease, Pathogenesis.
• Schwartz's Principles of Surgery makes the same point: new-onset diabetes can be an early manifestation of pancreatic cancer - Schwartz's Principles of Surgery, 11th Ed, Neoplasms of the Exocrine Pancreas.
• This is most relevant if the diabetes is new, or if she has weight loss, abdominal or back pain, jaundice or poor appetite.

• Missed or stopped medicines, or too low a dose.
• Steroids or other drugs that raise glucose.
• Infection or another acute illness.
• Diet and inactivity.

How doctors tell them apart

• History: Is the diabetes known and for how long? What are her medications? Has she lost weight? Does she have symptoms such as thirst, frequent urination or abdominal pain?
• Fasting or random C-peptide with paired glucose. A low C-peptide means the pancreas is making little insulin. A normal or high one points to insulin resistance.
• Autoantibodies (GAD65, and others): These are checked if type 1 or LADA is suspected.
• Ketones, kidney function, electrolytes and urine tests: These look for complications.
• Pancreatic imaging (ultrasound, CT or MRI): Used if the diabetes is new or she has weight loss or abdominal symptoms.

Practical point

Why C-peptide and not insulin

• It lasts longer in blood than insulin, so the level is steadier.
• It isn't affected by injected insulin, so it still works if she is already on insulin.
• It isn't picked up by most insulin assays.

Test options

Interpreting the result

• Very low or undetectable C-peptide means severe insulin deficiency. This suggests type 1 or late-stage beta cell failure, or pancreatic damage. Henry's lists C-peptide as "very low or undetectable" in type 1 and "detectable" in type 2 - Henry's, Characteristics of Type 1 and Type 2 Diabetes Mellitus.
• Normal or high C-peptide means she is still making insulin. This points to insulin resistance, which is typical type 2 diabetes.
• Intermediate values: The ADA Standards of Care say values of 200-600 pmol/L (0.6-1.8 ng/mL) are usually consistent with type 1 diabetes or MODY, but may be seen in insulin-treated type 2. Check the ADA diagnosis and classification section for the exact cutoffs. Your lab's reference range also matters.

Cautions for her case

• Take the glucose at the same time as the C-peptide. A low C-peptide at a very high glucose means more than a low C-peptide at a normal glucose. Some labs and clinicians repeat the test after glucose is brought under better control. Glucotoxicity can temporarily suppress insulin secretion and make the pancreas look worse than it is.
• Kidney function matters. The kidneys clear C-peptide, so reduced eGFR (common at 76) can raise the level falsely.
• Timing: Avoid doing it during acute illness or ketosis, and check which medicines she is on. Sulfonylureas increase C-peptide.

Other tests to consider

• GAD65 antibodies, with IA-2 and ZnT8 if needed, when type 1 or LADA is possible. Henry's lists these as the main pancreatic autoantibodies - Henry's, Key Points.
• Ketones, kidney function, electrolytes and a CBC.
• Pancreatic imaging (ultrasound, CT or MRI) if the diabetes is new or she has weight loss or abdominal pain. This is because of the link between new-onset diabetes and pancreatic cancer noted earlier.

Practical summary