Last Modified: 2:06pm 08/04/2021

Classification and Diagnosis of Hyperglycaemia

History is extremely important to determine whether a patient has new-onset hyperglycaemia as opposed to untreated or poorly controlled pre-existing diabetes mellitus. Distinguishing between type 1 diabetes mellitus and type 2 diabetes mellitus, along with new-onset hyperglycaemia, can help establish a clear plan for glycaemic control during hospital admission. For example, a higher vigilance for diabetic ketoacidosis is important in patients with type 1 diabetes

Transient hyperglycaemia

Development of hyperglycaemia is related to the onset of stress (e.g., infection or myocardial infarction), drugs such as corticosteroids, or enteral and parenteral nutrition, with resolution when the inciting factor is removed.

Tests:

  • HbA1c is normal if the period of stress or exposure is short (reflecting normal blood glucose before the illness).

Type 1 diabetes mellitus

May have a genetic predisposition and usually presents at a young age (5-15 years old). May have history of polyuria, polydipsia, and unintentional weight loss.

Tests:

Two out of the following tests, or the same test performed twice if the patient does not have unequivocal symptoms of hyperglycaemia:

  • Fasting plasma glucose: ≥7 mmol/L (≥126 mg/dL)
  • Oral glucose tolerance test: 2-hour plasma glucose ≥11.1 mmol/L (≥200 mg/dL). This test is generally not necessary
  • HbA1c ≥48 mmol/mol (≥6.5%).

In a patient with unequivocal symptoms of hyperglycaemia:

  • Random plasma glucose ≥11.1 mmol/L (≥200 mg/dL).

Supporting evidence for type 1 diabetes:

  • Plasma and urine ketones: elevated in ketoacidosis
  • Fasting C-peptide: usually low but may be in the normal range
  • Anti-glutamic acid decarboxylase (GAD) antibodies, islet cell antibodies (ICA), insulinoma-associated protein-2 (IA-2) antibodies: positive.

Type 2 diabetes mellitus

Usually older age. May have family history. Higher risk in black, Latino, and American Indian people.

May have features of metabolic syndrome (hypertension, obesity, and hyperlipidaemia).

Polyuria, polydipsia, and unintentional weight loss may occur.

May have indication of associated insulin resistance: for example, acanthosis nigricans or polycystic ovary syndrome (PCOS).

Tests:

Two out of the following tests, or the same test performed twice if the patient does not have unequivocal symptoms of hyperglycaemia:

  • Fasting plasma glucose: ≥7 mmol/L (≥126 mg/dL)
  • Oral glucose tolerance test: 2-hour plasma glucose ≥11.1 mmol/L (≥200 mg/dL). This test is generally not necessary
  • HbA1c ≥48 mmol/mol (≥6.5%).

In a patient with unequivocal symptoms of hyperglycaemia:

  • A random plasma glucose ≥11.1 mmol/L (≥200 mg/dL).

Pre-diabetes

Risk factors and history similar to those of type 2 diabetes.

Tests:

  • Impaired fasting glucose: fasting plasma glucose 5.55 mmol/L to 6.9 mmol/L (100-125 mg/dL)
  • Impaired glucose tolerance: oral glucose tolerance test 2-hour plasma glucose 7.8 mmol/L to 11 mmol/L (140-199 mg/dL)
  • HbA1c: 38 mmol/mol to 47 mmol/mol (5.7-6.4%).

Diabetes presenting during pregnancy

  • Overt diabetes – this is diagnosed at the initial antenatal visit when any one of the following has been satisfied:
    • Fasting plasma glucose ≥7 mmol/L (≥126 mg/dL)
    • HbA1c ≥48 mmol/mol (≥6.5%)
    • Random plasma glucose ≥11.1 mmol/L (≥200 mg/dL) that is confirmed by either the fasting plasma glucose or the HbA1c criterion above.
  • Gestational diabetes – this is diagnosed in two ways: a one-step or two-step method.One-step method
    • 75-g oral glucose tolerance test during 24-28 weeks of gestation.The diagnosis of gestational diabetes is met when any of the following values are met:
      • Fasting plasma glucose >5.1 mmol/L (>92 mg/dL)
      • 1 hour >10.0 mmol/L (>180 mg/dL)
      • 2 hour >8.5 mmol/L (>153 mg/dL).

    Two-step method

    • 1 hour 50-g screen, followed by a 3-hour 100-g oral glucose tolerance test for those with a 50-g screen 1 hour postprandial glucose >7.8 mmol/L (>140 mg/dL).The diagnosis of gestational diabetes is met when at least two of the following are met or exceeded:

      Carpenter/Coustan criteria (National Diabetes Data Group criteria)

      • Fasting: 5.3 mmol/L (95 mg/dL) (5.8 mmol/L [105 mg/dL])
      • 1 hour: 10.0 mmol/L (180 mg/dL) (10.5 mmol/L [190 mg/dL])
      • 2 hour: 8.6 mmol/L (155 mg/dL) (9.2 mmol/L [165 mg/dL])
      • 3 hour: 7.8 mmol/L (140 mg/dL) (8.1 mmol/L [145 mg/dL]).

Risk factors for gestational diabetes include elevated BMI, previous baby weighing >4.1 kg (>9 lb), hypertension, PCOS, non-white ancestry, and family history of diabetes.

BMJ Best Practice 2021