Review Question - QID 213453

A 55-year-old man presents to his primary care physician for a general checkup. The patient has a past medical history of diabetes, hypertension, and atrial fibrillation and is currently taking warfarin, insulin, lisinopril, and metoprolol. The patient’s brother recently died from a heart attack and he has switched to an all vegetarian diet in order to improve his health. His temperature is 98.6°F (37.0°C), blood pressure is 135/88 mmHg, pulse is 90/min, respirations are 17/min, and oxygen saturation is 98% on room air. The patient’s physical exam is unremarkable. His laboratory values are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 7,550/mm^3 with normal differential
Platelet count: 197,000/mm^3
INR: 1.0

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL

Which of the following is the best explanation for this patient’s laboratory values?