The numbers on the fingertip monitor made no sense. Over a matter of seconds, the pulse oximeter clipped to an adult woman's finger bounced among readings of roughly 40, 50, and more than 100 beats per minute. The woman felt fine, and her heart turned out to be beating normally. The likely cause was a coat of white nail polish.
The case is described in a report published in January 2026 in the journal Cureus by Akhtar Purvez, of Lincoln Memorial University DeBusk College of Osteopathic Medicine in Harrogate, Tennessee. The case report on erratic oximeter pulse readings involves just one patient, but it points to something most people never consider when they slip a pulse oximeter onto a finger: the heart rate on the screen is calculated from light, not read directly from the heart.
