Clinical Laboratory - Chemical Pathology and Immunology

Diabetes Mellitus

Diabetes mellitus (DM) types 1 and 2 are characterized by hyperglycemia. The two measures are:

• fasting blood glucose of ≥ 126 mg/dL, and
• hemoglobin A1C > 6.5%.

The less commonly performed glucose tolerance test is diagnostic for DM when the 2-hour plasma glucose is ≥ 200 mg/dL.

DM type 1 is characterized by an absolute decrease in plasma insulin. Plasma C-peptide is secreted along with insulin. Persons with DM type 1 usually have insulin antibodies and low C-peptide levels.

For short-term control of DM in monitoring response to insulin injections or to oral agents, the plasma glucose is monitored.

The hemoglobin A1C (glycated hemoglobin) gives a better indication of glucose control over time, since only about 1% of RBCs are replaced each day. Hyperglycemia leads to end-glcosylation of proteins, including hemoglobin.

Diabetes Mellitus Complications

Diabetic Ketoacidosis (DKA) and Nonketotic Hyperosmolar Coma

Diabetic ketoacidosis is a complication of DM type 1, with an absolute decrease in insulin. This means that about 2/3 of body mass (muscle and adipose tissues that require insulin for glucose uptake) begin to metabolize fatty acids, resulting in production of ketoacids and metabolic acidosis with anion gap. The respiratory rate increases to compensate (Kussmaul respirations). Typical laboratory findings with diabetic ketoacidosis:

Electrolytes

• Na 130 mEq/L (normal 136 - 145 mEq/L )
• K 5 mEq/L (normal 3.5 - 5.0 mEq/L )
• Cl 95 mEq/L (normal 95 - 105 mEq/L )
• HCO₃ 8 mEq/L (normal 22 - 28 mmol/L)

Osmolality 320 mOsm/L (normal 275 - 295 mOsmo/L)

Glucose 500 mg/dL (normal 70 - 110 mg/dL fasting)

Urine ketones 4+

Urine glucose 4+

Blood Gas Findings (Metabolic acidosis with respiratory compensation)

• PaO₂ 110 mm Hg (normal 80 - 100 mm Hg )
• PaCO₂ 23 mm Hg (normal 35 - 45 mm Hg )
• HCO₃ 8 mEq/L (normal 21 - 29 mEq/L)
• pH 7.15 (normal 7.35 - 7.45)

---

Nonketotic hyperosmolar coma is a complication of DM type 2, because there is generally enough insulin present to prevent ketoacidosis, but not enough to keep glucose from rising. There is generally some degree of dehydration that exacerbates serum electrolyte and glucose concentrations.

Electrolytes

• Na 150 mEq/L (normal 136 - 145 mEq/L )
• K 5 mEq/L (normal 3.5 - 5.0 mEq/L )
• Cl 115 mEq/L (normal 95 - 105 mEq/L )
• HCO₃ 25 mEq/L (normal 22 - 28 mmol/L)

Osmolality 330 mOsm/L (normal 275 - 295 mOsmo/L)

Glucose 900 mg/dL (normal 70 - 110 mg/dL fasting)

Urine ketones negative to 1+

Urine glucose 4+