INTRODUCTION:Hydroxyurea is an antimetabolite that acts by inhibiting synthesis of DNA. In addition to cancer therapy, it is also used to treat sickle cell anemia. However, daily use of hydroxyurea is not without risk, and one of the lesser-known sideeffects is discoloration of the nails-specifically melanonychia (brown lines) and blue lunula (nailbed crescents). The latter finding is extremely rare; only 2 case reports exist in the literature regarding blue lunula, but neither addresses its effects on oxygen saturation measurements. It is a well-established fact that black, green, and blue nail polish can falsely lower pulse oximetry readings. In our patient, her blue lunula at the base of her fingernails caused a similar artifact. Our case highlights the need for recognition of this rare phenomenon to avoid unnecessary workup of hypoxemia.
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