Is a fasting plasma glucose level of hyperglycemia indicative of diabetes mellitus?

Diagnosing Diabetes with a Fasting Blood Sugar of 250 mg/dL

Yes, a fasting plasma glucose level of 250 mg/dL definitively diagnoses diabetes mellitus, as it significantly exceeds the diagnostic threshold of 126 mg/dL. 1

Diagnostic Criteria for Diabetes

According to the American Diabetes Association guidelines, diabetes can be diagnosed using any of the following criteria:

1. Fasting plasma glucose (FPG) ≥126 mg/dL (7.0 mmol/L)

   • Fasting is defined as no caloric intake for at least 8 hours
   • A value of 250 mg/dL is well above this threshold

2. 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test

3. A1C ≥6.5% (48 mmol/mol)

4. Random plasma glucose ≥200 mg/dL (11.1 mmol/L) with symptoms of hyperglycemia 1

Clinical Significance of a 250 mg/dL Fasting Glucose

A fasting glucose of 250 mg/dL falls into the category of "severe hyperglycemia" as defined by the American Academy of Pediatrics 1. This level of hyperglycemia:

• Is nearly twice the diagnostic threshold for diabetes (126 mg/dL)
• Indicates significant impairment in glucose metabolism
• Requires prompt medical attention and treatment
• Places the patient at immediate risk for symptoms of hyperglycemia (polyuria, polydipsia, weight loss)

Confirmation Requirements

While a single fasting glucose of 250 mg/dL strongly indicates diabetes, standard practice requires confirmation:

• In the absence of unequivocal hyperglycemia with classic symptoms, diagnosis requires two abnormal test results from the same sample or in two separate test samples 1
• However, with a value as high as 250 mg/dL, especially if symptoms are present, immediate treatment may be warranted while awaiting confirmation

Pathophysiology Behind Elevated Fasting Glucose

A fasting glucose of 250 mg/dL typically reflects:

• In type 2 diabetes: A combination of insulin resistance and impaired insulin secretion
• In type 1 diabetes: Significant insulin deficiency due to autoimmune destruction of beta cells
• In both cases: Excessive hepatic glucose production during fasting periods 2

Clinical Approach

When encountering a patient with a fasting glucose of 250 mg/dL:

1. Assess for symptoms of hyperglycemia (polyuria, polydipsia, unexplained weight loss)
2. Evaluate for complications that may require urgent treatment:
   • Check for signs of diabetic ketoacidosis (DKA) in suspected type 1 diabetes
   • Assess for hyperosmolar hyperglycemic state, especially in elderly patients 3
3. Obtain additional laboratory tests:
   • HbA1c to assess chronic glycemic control
   • Basic metabolic panel to evaluate electrolytes and kidney function
   • Urinalysis to check for ketones and glucose

Common Pitfalls to Avoid

1. Delaying diagnosis or treatment when fasting glucose is significantly elevated

   • A value of 250 mg/dL requires prompt attention, not just watchful waiting

2. Failing to consider type 1 diabetes in adults

   • While type 2 diabetes is more common, autoimmune diabetes can occur at any age

3. Not checking for acute complications in patients with severe hyperglycemia

   • Patients with values >250 mg/dL may be at risk for acute metabolic decompensation

4. Ignoring factors that might affect glucose readings

   • Certain medications, acute illness, or stress can temporarily elevate glucose levels

In conclusion, a fasting plasma glucose of 250 mg/dL is diagnostic of diabetes mellitus, exceeding the established threshold by a substantial margin. This finding warrants immediate clinical attention, appropriate follow-up testing, and prompt initiation of treatment to prevent complications associated with persistent hyperglycemia.