Which battery of tests is most useful in evaluating an anion gap of 22 mEq/L?

• A. Calcium, Magnesium, Phosphate, and pH
• B. BUN, Creatinine, Salicylate, and Methanol
• C. AST, ALT, LD, and Amylase
• D. Glucose, CK, Myoglobin, and Cryoglobulin

Answer: (B)

An elevated anion gap points to the presence of unmeasured anions in the blood, often from toxins or renal failure. To evaluate a gap of 22 mEq/L, you want tests that can reveal common contributors such as toxin ingestion or impaired renal excretion. Checking salicylate and methanol levels directly targets two classic toxin-related causes of high anion gaps. Adding BUN and creatinine assesses renal function and potential uremic acidosis, another common source of unmeasured acidic components. Together, this battery directly addresses the main culprits behind an increased anion gap.

The other panels don’t specifically probe these etiologies. Calcium, magnesium, phosphate, and pH do not identify the cause of the gap, and while pH is part of acid-base status, it doesn’t reveal the source. Liver enzymes and amylase focus on hepatic or pancreatic issues rather than the unmeasured anions driving the gap. The glucose, CK, myoglobin, and cryoglobulin panel likewise targets muscle or protein-related problems, not the metabolic acids that create a high anion gap.