Soru

A 34-year-old woman with a history of systemic lupus erythematosus and Sjögren syndrome is evaluated in the emergency department for progressive muscle weakness over the past 3 days. She reports difficulty climbing stairs and getting out of chairs. She has not had diarrhea or vomiting. Her blood pressure is 112/76 mm Hg, and her pulse is 88/min. Physical examination shows 3/5 motor strength in the proximal lower extremities. Laboratory results are as follows:

Serum:
Sodium: $138$ mEq/L
Potassium: $2.4$ mEq/L
Chloride: $115$ mEq/L
Bicarbonate: $13$ mEq/L

Arterial blood gas (room air):
pH: $7.27$
pCO2: $28$ mm Hg

Urine:
Sodium: $42$ mEq/L
Potassium: $35$ mEq/L
Chloride: $51$ mEq/L

To help determine the etiology of this patient's acid-base disturbance, the physician evaluates her urinary electrolytes. What is this patient's urine anion gap in mEq/L?