A 55-year-old man comes to the hospital due to progressive fatigue and weakness. Medical history includes type 2 diabetes mellitus and obesity. Laboratory results are as follows: Which of the following is the most likely diagnosis?

Question

A 55-year-old man comes to the hospital due to progressive fatigue and weakness.  Medical history includes type 2 diabetes mellitus and obesity.  Laboratory results are as follows:  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec160b_3cfb_8318_9249_4785ac4bca64_MD0001_00 This patient has low serum bicarbonate (HCO₃⁻) (<24 mEq/L), consistent with metabolic acidosis. The anion gap is normal at 10 mEq/L; therefore, the most likely diagnosis is renal tubular acidosis, a common cause of nonanion gap metabolic acidosis (NAGMA). NAGMA results from loss of HCO₃⁻ (usually from the kidneys or gastrointestinal tract), leading to a relative increase in H⁺. In renal tubular acidosis, there is either impaired proximal tubular HCO₃⁻ reabsorption (type 2) or impaired distal tubular H⁺ secretion (types 1 and 4) leading to net HCO₃⁻ loss. Severe diarrhea, involving loss of HCO₃⁻ in the stool, is another common cause of NAGMA. NAGMA is also referred to as hyperchloremic acidosis because the decrease in serum HCO₃⁻ is compensated for by an increase in serum Cl⁻ to maintain electronegative balance. (Choices A and B) Anion gap metabolic acidosis results from the addition of unmeasured acidic compounds to the blood. The compounds donate H⁺ to bind up serum HCO₃⁻, reducing buffering capacity and causing metabolic acidosis. The remaining anionic component increases the anion gap. Common etiologies of anion gap metabolic acidosis include increased production of ketones (eg, acetoacetate, beta-hydroxybutyrate), which occurs with diabetic ketoacidosis, and increased production of lactic acid, which occurs with reduced organ and tissue perfusion (eg, sepsis). (Choice C) Hypoventilation causes retention of CO₂ and respiratory acidosis. A compensatory metabolic alkalosis with increased serum HCO₃⁻ (>24 mEq/L) is expected. (Choice D) Primary hyperaldosteronism causes excessive loss of H⁺ from the renal tubular collecting duct, leading to metabolic alkalosis with increased serum HCO₃⁻. Educational objective: Nonanion gap metabolic acidosis (NAGMA) results from the loss of bicarbonate (HCO₃⁻) (usually from the kidneys or gastrointestinal tract), leading to a relative increase in H⁺. Common causes include renal tubular acidosis and severe diarrhea. NAGMA is also referred to as hyperchloremic acidosis because the decrease in serum HCO₃⁻ is compensated for by an increase in serum chloride to maintain electronegative balance. __________ References: Hyperchloremic acidosis. (http://www.ncbi.nlm.nih.gov/pubmed/29493965)

A 55-Year-Old Man Comes to the Hospital Due to Progressive