A New High Affinity Hemoglobin Variant: Hb San Francisco-KP (HBB: c.104T>C).

The evaluation of erythrocytosis can fail to detect hemoglobin (Hb) variants if a thorough and systemic investigation is not undertaken. Here we report the identification of a novel high-oxygen affinity Hb that was previously misclassified as polycythemia vera (PV). Given that treatment recommendations can vary significantly based on the etiology of erythrocytosis, familiarity with reference laboratories and their methodologies is of crucial importance to conducting a precise consultation, as in the case of our Hb variant, named Hb San Francisco-KP [β34(B16)Val→Ala, HBB: c.104T>C] for the city and medical center where it was discovered. The Mayo Clinic's (Rochester, MN, USA) Erythrocytosis Evaluation (REVE) panel was instrumental in establishing a final diagnosis. Of note, the patient's clinical response to phlebotomy distinguishes this subtype from many of the other high affinity Hbs where the erythrocytosis is primarily compensatory and not in need of venesection.