What is the appropriate workup and management for an adult patient with a history of diabetes presenting with hyperglycemia (elevated blood sugar)?

Workup for Blood Sugar of 300 mg/dL

For a blood sugar of 300 mg/dL, immediately assess whether the patient is critically ill or non-critically ill, check for symptoms of diabetic ketoacidosis (DKA), and initiate insulin therapy while investigating the underlying cause of hyperglycemia. 1

Immediate Assessment

Determine clinical status:

• Critically ill patients (ICU, sepsis, post-operative, hemodynamically unstable) require continuous IV insulin infusion starting when blood glucose exceeds 180 mg/dL, targeting 140-180 mg/dL 1
• Non-critically ill patients should receive subcutaneous basal-bolus insulin regimen targeting pre-meal glucose <140 mg/dL and random glucose <180 mg/dL 1

Screen for DKA immediately if the patient has type 1 diabetes or is insulin-dependent, looking for drowsiness, flushed face, thirst, fruity breath odor, nausea, vomiting, or abdominal pain 2

• Check blood glucose, serum ketones (or urine ketones), and venous blood gas if DKA is suspected 1
• DKA requires continuous IV insulin infusion and aggressive fluid resuscitation 1

Diagnostic Workup

Identify the cause of hyperglycemia:

• New-onset diabetes: Check HbA1c to distinguish acute hyperglycemia from chronic uncontrolled diabetes 1
• Known diabetes with poor control: Review medication adherence, recent illness, infections (especially urinary tract, respiratory, skin), or new medications (particularly corticosteroids) 2
• Stress hyperglycemia: Consider acute myocardial infarction, stroke, sepsis, or surgical stress in patients without prior diabetes diagnosis 1

Laboratory evaluation:

• HbA1c to assess chronic glycemic control 1
• Basic metabolic panel to check for renal function and electrolyte abnormalities 3
• Urinalysis to detect glucosuria (occurs when blood glucose exceeds renal threshold ~180 mg/dL) and rule out urinary tract infection 1
• If infection suspected: complete blood count, blood cultures, chest X-ray, or other site-specific cultures 1

Insulin Therapy Initiation

For critically ill patients:

• Start continuous IV insulin infusion when blood glucose >180 mg/dL 1, 4
• Target blood glucose 140-180 mg/dL using a validated protocol with adjustments every 30 minutes to 2 hours 1, 4
• Monitor blood glucose every 1-2 hours during IV insulin infusion 4

For non-critically ill patients with known diabetes:

• Calculate total daily insulin dose: 0.3-0.5 units/kg/day for patients with severe hyperglycemia (blood glucose ≥300 mg/dL) 5, 6
• Divide as 50% basal insulin (given once daily as glargine or detemir) and 50% prandial insulin (divided before meals as rapid-acting analog) 1, 5
• Example: For a 70 kg patient: 0.4 units/kg/day = 28 units total daily dose → 14 units basal insulin once daily + 4-5 units rapid-acting insulin before each meal 5

For insulin-naive patients with new diabetes:

• Start with 10 units of basal insulin once daily OR 0.1-0.2 units/kg/day 5
• For severe hyperglycemia (≥300 mg/dL), consider starting at 0.3-0.4 units/kg/day 5
• Continue metformin unless contraindicated 5

Critical Pitfalls to Avoid

Never use sliding scale insulin as monotherapy – this approach is explicitly condemned by all major guidelines and results in reactive treatment rather than prevention of hyperglycemia 1, 6, 7, 8

Do not delay insulin therapy in patients with blood glucose ≥300 mg/dL, as this prolongs hyperglycemia exposure and increases complication risk 5

Avoid aggressive targets (<110 mg/dL) as these significantly increase hypoglycemia risk without mortality benefit 1

Do not attribute hyperglycemia solely to diabetes without investigating precipitating factors like infection, myocardial infarction, or medication changes 1, 2

Monitoring Requirements

• Check blood glucose every 4-6 hours initially for subcutaneous insulin regimens 6
• Adjust insulin doses daily based on glucose patterns 1
• Monitor for hypoglycemia symptoms (sweating, tremor, confusion, palpitations) and treat immediately with 15 grams of fast-acting carbohydrate if blood glucose <70 mg/dL 2
• Reassess clinical status daily and transition from IV to subcutaneous insulin when clinically stable, giving subcutaneous insulin 1-2 hours before discontinuing IV insulin 4