MIT researchers have developed a way to measure white blood cell levels by imaging the cells as they flow through capillaries at the base of the fingernail; the white blood cells are marked by crosses. (Credit: MIT/The Leuko Project)

One of the major side effects of chemotherapy is a sharp drop in white blood cells, which leaves patients vulnerable to dangerous infections. Researchers have now developed a portable device that could be used to monitor patients' white blood cell levels at home, without taking blood samples.

Such a device could prevent thousands of infections every year among chemotherapy patients, the researchers say. Their 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 the researchers used to tackle this problem consists of a wide-field microscope that emits blue light, which penetrates about 50-150 µm below the skin and is reflected back to a video camera. The researchers decided to image the skin 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.

The research team has applied for patents on the technology and has launched a company called Leuko, which is working on commercializing the technology.