The patient whose blood smear is shown in the photograph was a 32-year-old female from Virginia who came to the high country of Colorado to ski.

The day after arrival, she experienced shortness of breath, fatigue, and upper abdominal pain. She was seen in a medical center in the mountains where a working diagnosis of altitude sickness was made.

• A CBC revealed RBCs 5.1 x 10¹²/L, hemoglobin 12.8g/dL, MCV 60fL, hematocrit 40.9%, and normal total WBC, differential, and platelet count. The RDW was normal.
• Further questioning revealed a previous diagnosis of heterozygous beta-chain thalassemia. No other abnormal hemoglobins were found on hemoglobin electrophoresis, but HbA-2 was elevated to 5%, supporting the diagnosis of beta thalassemia.
• The patient's poikylocytosis and anisocytosis may be a clue to an underlying erythrocyte abnormality.
• Persons with iron deficiency anemia may experience various degrees of hypoxia upon arriving at high altitudes. Those with sickle cell disease and thalassemia minor (as in this case) may experience bone pain or other symptoms of "crisis" and/or alteration in the appearance of their erythrocytes upon sudden high altitude exposure.
• The classic teaching is that in differentiating iron deficiency anemia from thalassemia, increased RDW would favor iron deficiency; normal RDW favors thalassemia.