Diagnosis: Type 2 Diabetes Mellitus
A random blood sugar (RBS) of 390 mg/dL without diabetic ketoacidosis (DKA) is most consistent with Type 2 diabetes mellitus, which accounts for 90-95% of all diabetes cases. 1
Key Diagnostic Reasoning
Why Type 2 Diabetes is the Primary Diagnosis
Type 2 diabetes is characterized by hyperglycemia with relative (rather than absolute) insulin deficiency and insulin resistance, distinguishing it from Type 1 diabetes which typically presents with absolute insulin deficiency 1
DKA seldom occurs spontaneously in Type 2 diabetes; when present, it usually requires specific precipitating factors such as infection (COVID-19, pneumonia), myocardial infarction, missed insulin doses in insulin-treated patients, illicit drug use (cocaine), or certain medications (glucocorticoids, second-generation antipsychotics, SGLT2 inhibitors) 1
The absence of DKA with significant hyperglycemia (390 mg/dL) strongly favors Type 2 diabetes over Type 1 diabetes, as Type 1 patients typically develop ketoacidosis when insulin deficient 1
Alternative Consideration: Hyperosmolar Hyperglycemic State (HHS)
HHS is more typically associated with Type 2 diabetes and is characterized by severe hyperglycemia, hyperosmolality, and dehydration in the absence of significant ketoacidosis 1
While RBS 390 mg/dL represents significant hyperglycemia, HHS typically presents with even higher glucose levels (often >600 mg/dL) and requires assessment of serum osmolality and mental status changes to confirm 2, 3
Patients can have mixed clinical features of both DKA and HHS, so complete metabolic evaluation is warranted 1
Confirmatory Testing Required
Essential Laboratory Workup
Obtain fasting plasma glucose, HbA1c, complete metabolic panel including serum electrolytes, and venous blood gas to confirm diabetes diagnosis and rule out metabolic acidosis 4
Check serum ketones (preferably β-hydroxybutyrate) and calculate anion gap using [Na⁺] - ([Cl⁻] + [HCO₃⁻]) to definitively exclude DKA 4
Measure serum osmolality to assess for HHS, particularly if the patient shows signs of severe dehydration or altered mental status 4
In younger adults without traditional risk factors for Type 2 diabetes, consider islet autoantibody testing (GAD65 autoantibodies) to exclude Type 1 diabetes 1
Diagnostic Criteria Confirmation
Diabetes is confirmed by any of the following: fasting plasma glucose ≥126 mg/dL, random plasma glucose ≥200 mg/dL with symptoms of hyperglycemia, 2-hour plasma glucose ≥200 mg/dL during oral glucose tolerance test, or HbA1c ≥6.5% 1
DKA is definitively excluded when: venous pH >7.3, serum bicarbonate ≥15 mEq/L, and anion gap ≤12 mEq/L 4
Critical Clinical Pitfalls to Avoid
Do not assume Type 2 diabetes is benign simply because DKA is absent—Type 2 diabetes frequently goes undiagnosed for years, and even undiagnosed patients are at increased risk of developing macrovascular and microvascular complications 1
Never overlook precipitating factors for hyperglycemia such as infection (urinary tract infection, pneumonia), myocardial infarction, or medication use (corticosteroids, atypical antipsychotics) that may require concurrent treatment 1, 5
Do not delay assessment for HHS in elderly patients or those with altered mental status, as HHS carries higher mortality than DKA despite lower incidence 6
Consider ketosis-prone Type 2 diabetes (KPD) in middle-aged, mildly obese, antibody-negative patients who present with significant hyperglycemia, as they can occasionally develop DKA without typical precipitating causes 6