One of the major side effects of chemotherapy is a sharp drop in white blood cells, which leaves patients vulnerable to dangerous infections. Chemotherapy patients usually receive a dose every 21 days. After each dose, their white blood cell levels fall and then gradually climb again. Doctors usually only test patients’ blood just before a new dose, so they have no way of knowing if white blood cell levels drop to dangerous levels following a treatment.
A new device could be used to monitor patients’ white blood cell levels at home, without taking blood samples. The tabletop prototype records video of blood cells flowing through capillaries just below the surface of the skin at the base of the fingernail. A computer algorithm can analyze the images to determine if white blood cell levels are below the threshold that doctors consider dangerous.
The technology consists of a wide-field microscope that emits blue light, which penetrates about 50 to 150 microns below the skin and is reflected back to a video camera. The skin is imaged at the base of the nail, known as the nailfold, because the capillaries there are located very close to the surface of the skin. These capillaries are so narrow that white blood cells must squeeze through one at a time, making them easier to see.
The technology does not provide a precise count of white blood cells, but reveals whether patients are above or below the threshold considered dangerous — defined as 500 neutrophils (the most common type of white blood cell) per microliter of blood.
An automated prototype was developed to demonstrate the system as a viable home-use device. The imaging must take place in the right spot on the patient’s finger, and the operation of the device must be straightforward. Using this new prototype, the device will be tested with additional cancer patients.
The technology also can be adapted to generate more precise white blood cell counts, which would make it useful for monitoring bone marrow transplant recipients or people with certain infectious diseases. This could also make it possible to determine whether chemotherapy patients can receive their next dose before 21 days have passed.