Medical Challenge Question 12 Hematology

A 24 year old Caucasian woman comes to the clinic with a complaint of worsening fatigue and dyspnea, which is most noticeable with exercise for the last 2 months. She otherwise feels well. She notes no gastrointestinal symptoms, fever, chills, diarrhea, or weight loss, but she believes that her urine sometimes appears darker than usual. She eats a balanced diet, has menstruation normal duration and flow, and she is physically active as a long distance marathon runner. Her medical and family histories are unremarkable; her only medication is ibuprofen as needed for mild aches and pains.

On exam, her temperature is 37.2°C , blood pressure is 104/56 mm Hg, pulse rate is 62 beats per minute, and respiration rate is 14 breaths per minute. She has no muscle tenderness or weakness and her physical examination is normal. A stool sample is guaiac negative.

Labs:

Haptoglobin Undetectable
Hematocrit 26%
Leukocyte count 5600/µL
Mean corpuscular volume 76 fL
Platelet count 410,000/µL
Reticulocyte count 1.4% of erythrocytes
Creatine kinase 149 U/L
Ferritin 5 ng/mL
Lactate dehydrogenase 1373 U/L
Urinalysis is positive for 4+ blood; 0-1 leukocytes/hpf, and 0 erythrocytes/hpf

Peripheral blood smear shows hypochromic microcytic erythrocytes without schistocytes or spherocytes.

Which of the following is the most likely cause of this patient's anemia?

A. Exercise-induced hematuria

B. Exercise-induced hemolysis

C. Inflammatory myopathy

D. Rhabdomyolysis

E. Inflammatory anemia

Reference:

Dang CV. Runner's anemia. JAMA. 2001 Aug 8;286(6):714-6. PMID: 11495622