Chemotherapy and other treatments that take down cancer cells can also destroy patients’ immune cells. Every year, that leads tens of thousands of cancer patients with weakened immune systems to contract infections that can turn deadly if unmanaged.

Doctors must strike a balance between giving enough chemotherapy to eradicate cancer while not giving so much that the patient’s white blood cell count gets dangerously low, a condition known as neutropenia. It can also leave patients socially isolated in between rounds of chemotherapy. Currently, the only way for doctors to monitor their patients’ white blood cells is through blood tests.

Now Leuko is developing an at-home white blood cell monitor to give doctors a more complete view of their patients’ health remotely. Rather than drawing blood, the device uses light to look through the skin at the top of the fingernail, and artificial intelligence to analyze and detect when white blood cells reach dangerously low levels.