What laboratory finding is most likely to be increased in a patient with diabetic ketoacidosis (DKA) and severe hyperglycemia?

Serum Osmolality is Most Likely Increased in Diabetic Ketoacidosis with Severe Hyperglycemia

In a 10-year-old girl with type 1 diabetes presenting with DKA (blood glucose 710 mg/dL, bicarbonate 6 mEq/L, ketone odor), serum osmolality is the laboratory finding most likely to be increased.

Clinical Presentation Analysis

This patient presents with classic signs of diabetic ketoacidosis (DKA):

• Diffuse abdominal pain, nausea, and vomiting
• Lethargy
• Ketone breath odor
• Deep respirations (Kussmaul breathing)
• Severe hyperglycemia (710 mg/dL)
• Severe metabolic acidosis (bicarbonate 6 mEq/L)

Laboratory Findings in DKA

Let's analyze each option systematically:

A) Arterial pH

• In DKA, arterial pH is decreased, not increased
• The patient's bicarbonate of 6 mEq/L indicates severe metabolic acidosis
• According to diagnostic criteria, DKA is associated with arterial pH <7.30 1

B) Serum C-peptide level

• C-peptide is produced in equimolar amounts with endogenous insulin
• In type 1 diabetes, especially during DKA, insulin and C-peptide levels are decreased due to beta-cell destruction
• C-peptide would be low, not elevated, in this scenario 1

C) Serum magnesium level

• Magnesium levels may be normal or decreased in DKA due to urinary losses
• Total body magnesium deficits in DKA range from 3-5 mmol/kg 1
• Magnesium is not typically elevated in DKA

D) Serum osmolality

• Serum osmolality is markedly increased in DKA due to severe hyperglycemia
• Calculated effective serum osmolality = 2[measured Na (mEq/L)] + glucose (mg/dL)/18 1
• With glucose of 710 mg/dL, osmolality would be significantly elevated
• Diagnostic criteria for HHS include effective serum osmolality >320 mOsm/kg H₂O, and DKA with severe hyperglycemia approaches this level 1

E) Serum phosphorus level

• While total body phosphorus is depleted in DKA, serum phosphorus may be normal or even elevated initially
• During treatment, phosphorus levels typically fall as phosphate reenters cells
• Initial elevation is not consistent or reliable 1

Pathophysiology of Increased Osmolality in DKA

The marked hyperglycemia (710 mg/dL) directly contributes to hyperosmolality:

• Each 100 mg/dL increase in glucose adds approximately 5.6 mOsm/kg to serum osmolality
• The patient's glucose of 710 mg/dL would contribute approximately 39.4 mOsm/kg to serum osmolality
• This hyperglycemia-induced hyperosmolality is a hallmark of DKA 1

Common Pitfalls in Laboratory Interpretation

1. Misinterpreting initial electrolyte values: While total body stores of potassium, phosphorus, and magnesium are depleted in DKA, serum levels may initially appear normal or even elevated due to extracellular shifts caused by acidosis and insulin deficiency.

2. Overlooking corrected sodium: Sodium concentration should be corrected for hyperglycemia (add 1.6 mEq/L to measured sodium for each 100 mg/dL of glucose above normal) 1.

3. Focusing only on glucose: While hyperglycemia is prominent, the metabolic derangements of DKA include multiple electrolyte abnormalities that require monitoring and correction.

Treatment Implications

Understanding the increased osmolality is critical for proper fluid management:

• Initial fluid therapy should be isotonic saline (0.9% NaCl) at 10-20 mL/kg/hour for the first hour 1
• Fluid replacement should correct estimated deficits within 24 hours
• The change in serum osmolality should not exceed 3 mOsm/kg/hour to avoid cerebral edema, particularly important in pediatric patients 1

In conclusion, of the laboratory parameters listed, serum osmolality is the only one that would be increased in this patient with DKA and severe hyperglycemia.