In an 80‑year‑old man with diabetes mellitus, hypertension, dyslipidemia on lisinopril, thiazide diuretic, and antidiabetic medications presenting with agitation and irritability, whose labs show serum sodium 121 mmol/L, potassium 5.9 mmol/L, calcium 2.8 mmol/L, and albumin 1.8 g/dL, which condition best describes his laboratory findings?

Hyponatremia Best Describes This Patient's Condition

The correct answer is A - Hyponatremia. This 80-year-old patient's agitation and irritability are most directly attributable to his severely low sodium level of 121 mmol/L, which represents moderate-to-severe hyponatremia requiring immediate attention 1, 2.

Clinical Reasoning

Why Hyponatremia is the Primary Diagnosis

• Sodium 121 mmol/L represents moderate hyponatremia (125-129 mEq/L is moderate; <125 mEq/L is severe), and this patient falls just above the severe threshold 2
• Neuropsychiatric symptoms including agitation, irritability, confusion, and altered mental status are classic manifestations of hyponatremia, particularly in elderly patients 2
• The combination of lisinopril (ACE inhibitor) and thiazide diuretic is a well-recognized cause of hyponatremia in elderly diabetic patients 1
• The American Geriatrics Society specifically warns that thiazides can cause severe hyponatremia and recommends close electrolyte monitoring, particularly when combined with ACE inhibitors 1

Why the Other Options Are Less Accurate

Hyperkalemia (Option B):

• While the potassium of 5.9 mEq/L is elevated and clinically significant, hyperkalemia does not typically cause agitation or irritability 3
• Hyperkalemia manifests with cardiac arrhythmias and muscle weakness when severe, not neuropsychiatric symptoms 3
• The hyperkalemia here is likely secondary to the combination of lisinopril and declining renal function from volume depletion caused by the thiazide 4, 3

Hypercalcemia (Option C):

• The calcium level of 2.8 mmol/L (approximately 11.2 mg/dL) appears elevated, but this is misleading given the severely low albumin 1
• Corrected calcium must be calculated when albumin is low (1.8 g/dL is severely low), as total calcium measurements are unreliable in hypoalbuminemia 1
• The corrected calcium is likely normal or only mildly elevated, making this an unlikely primary cause of symptoms

Hypoalbuminemia (Option D):

• While albumin of 1.8 g/dL is severely low, hypoalbuminemia alone does not cause acute agitation or irritability 1
• Hypoalbuminemia is a chronic condition that affects oncotic pressure and fluid distribution but does not produce acute neuropsychiatric symptoms

Mechanism of Thiazide-Induced Hyponatremia

• Thiazide diuretics impair free water excretion and can cause profound hyponatremia, especially in elderly patients 1, 5
• The combination with lisinopril compounds the risk through multiple mechanisms including volume depletion and altered renal sodium handling 4, 1
• Elderly diabetic patients are at particularly high risk for thiazide-induced electrolyte disturbances 1, 5

Immediate Management Priorities

The American Geriatrics Society recommends:

• Discontinue the thiazide diuretic immediately in patients with severe hyponatremia 1
• Monitor electrolytes closely to prevent osmotic demyelination syndrome during correction 1
• Electrolyte monitoring should occur within 1-2 weeks of thiazide initiation, with dose increases, and at least yearly 1

For the hyperkalemia:

• Discontinue or reduce lisinopril immediately when potassium >5.5 mEq/L, particularly with declining renal function 3
• Recheck potassium and creatinine within 24-48 hours after stopping lisinopril 3
• Obtain ECG to assess for hyperkalemia-related cardiac changes 3

Common Pitfall to Avoid

Do not be distracted by multiple abnormal laboratory values. While this patient has several electrolyte derangements, the clinical presentation of agitation and irritability points specifically to hyponatremia as the primary problem. The hyperkalemia, while requiring treatment, does not explain the neuropsychiatric symptoms 3, 2.