What are the causes of consistently elevated blood sugar levels in a type 1 diabetic?

Causes of Consistently Elevated Blood Sugar in Type 1 Diabetes

The most common cause of persistent hyperglycemia in type 1 diabetes is insufficient insulin dosing—either inadequate total daily dose, improper basal-to-bolus ratio, or complete discontinuation of insulin therapy. 1, 2

Primary Insulin-Related Causes

Insufficient Insulin Provision

• Inadequate total daily insulin dose is the fundamental cause, as type 1 diabetes is characterized by absent or near-absent β-cell function requiring complete external insulin replacement 1
• Discontinuation or omission of insulin is the most common preventable cause of hyperglycemia and can rapidly progress to diabetic ketoacidosis (DKA), a life-threatening emergency 3, 2
• Inappropriate basal-bolus balance contributes to persistent hyperglycemia when the typical 50:50 split between basal and prandial insulin is not maintained 1, 4

Insulin Delivery Problems

• Injection site issues including lipodystrophy can delay insulin absorption and cause erratic glucose control 2
• Intramuscular rather than subcutaneous injection results in faster, more extensive absorption that doesn't provide sustained coverage 2
• Pump malfunction or disconnection in patients using continuous subcutaneous insulin infusion can rapidly lead to hyperglycemia and ketoacidosis within 12 hours 1

Medication and Dosing Errors

Carbohydrate-Insulin Mismatch

• Failure to match prandial insulin to carbohydrate intake is a critical error, as total carbohydrate content determines premeal insulin dosage and postprandial glucose response 1
• Fixed insulin regimens without dose adjustment for varying carbohydrate intake lead to consistent postprandial hyperglycemia 1
• Patients who adjust premeal insulin based on carbohydrate changes achieve A1C levels 1.0% lower than those who don't 1

Inadequate Insulin Intensification

• Failure to increase insulin during periods of increased need such as puberty, pregnancy, or medical illness results in persistent hyperglycemia 1
• Typical insulin requirements range from 0.4 to 1.0 units/kg/day, with higher amounts required during these physiologic stress periods 1

Physiologic and Pathophysiologic Factors

Stress and Illness

• Medical illness increases insulin requirements due to stress hyperglycemia and counterregulatory hormone release 1
• Infection or other acute stress can rapidly convert modest hyperglycemia to severe hyperglycemia or DKA 1

Metabolic Decompensation

• Systematic metabolic disturbances including hypertriglyceridemia occur when insulin provision is insufficient, further worsening hyperglycemia 1
• Tissue catabolism from insulin deficiency contributes to ongoing glucose production 1

Gastroparesis

• Delayed gastric emptying in diabetic patients can cause unpredictable glucose patterns, though acute hyperglycemia itself directly impairs gastric motility, creating a vicious cycle 3

Behavioral and Educational Factors

Knowledge Deficits

• Lack of education on insulin adjustment for premeal glucose levels and anticipated physical activity leads to persistent hyperglycemia 1
• Inadequate carbohydrate counting skills prevent appropriate prandial insulin dosing 1

Non-Adherence

• Intentional insulin omission occurs in some patients, particularly adolescents and young adults
• Missed injections in multiple daily injection regimens create gaps in insulin coverage

Critical Pitfalls to Avoid

Never assume hyperglycemia alone rules out hypoglycemia as a contributing factor—patients with recurrent hypoglycemia may overtreat episodes, leading to rebound hyperglycemia and a pattern of glucose variability 4

Never attribute all hyperglycemia to dietary indiscretion—this overlooks the fundamental issue of inadequate insulin dosing that must be addressed first 1

Never delay insulin dose adjustment waiting for "perfect" adherence—insufficient insulin provision causes not only hyperglycemia but also metabolic disturbances and tissue catabolism that worsen outcomes 1

Diagnostic Approach

When evaluating persistent hyperglycemia, systematically assess:

• Total daily insulin dose relative to body weight (should be 0.4-1.0 units/kg/day, higher during puberty/pregnancy/illness) 1
• Basal-bolus distribution (typically 50:50 split) 1
• Injection technique and site rotation to identify lipodystrophy or improper administration 2
• Carbohydrate intake patterns and whether prandial insulin is appropriately matched 1
• Presence of intercurrent illness requiring insulin dose escalation 1
• Blood or urine ketones to rule out impending DKA, which requires immediate hospitalization 3

The FDA label for insulin detemir explicitly warns that "inadequate dosing or discontinuation of treatment may lead to hyperglycemia and, in patients with type 1 diabetes, diabetic ketoacidosis" 2, emphasizing that insufficient insulin is the primary modifiable cause requiring immediate attention.