Review Question - QID 110021

A 45-year-old African-American man presents to his primary care physician with a chief concern of constant fatigue. He states that it started a few days ago and has been steadily worsening. The patient has a past medical history of constipation and depression and is currently taking TMP-SMX for a urinary tract infection. He went to the emergency department for an episode of severe and diffuse pain 2 months ago. The patient is a vegan and lives with his wife. His temperature is 98.3°F (36.8°C), blood pressure is 129/68 mmHg, pulse is 100/min, respirations are 15/min, and oxygen saturation is 98% on room air. Laboratory values are obtained and shown below.

Hemoglobin: 9 g/dL
Hematocrit: 30%
Leukocyte count: 6,500/mm^3 with normal differential
Platelet count: 197,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 5.3 mEq/L
HCO3-: 25 mEq/L
BUN: 27 mg/dL
LDH: 544 U/L
Coombs test: Positive
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 9.9 mg/dL
AST: 12 U/L
ALT: 10 U/L

A peripheral smear is ordered as seen in Figure A. Which of the following is the most likely diagnosis?