New Portable Device Counts Leukocytes Through the Skin

A novel way to count white blood cells without a blood test, simply by applying a small device on the fingertip, is being developed.

The technology, which combines an optical sensor with algorithms, has already three prototypes on the go and is specially designed to be used on chemotherapy patients, who could know their immune system levels in real time.

A collaboration between scientific centers and hospitals in the region of Madrid with the Massachusetts Institute of Technology (MIT; Cambridge, MA, USA) and other centers in the Boston area (MA, USA), observed that immunosuppression (low white blood cell counts) is the main side effect for chemotherapy patients, which leads to possible infections, hospitalizations, treatment delays and shorter life expectancy.

The team is developing a portable device capable of counting white blood cells in real time, without requiring a blood test. The system includes an innovative optics sensor through the skin that can observe white cells as they flow past a miniature lens. This new device, potentially on the market in 2019, could be applied to improve the treatment of patients who are left immunosuppressed after chemotherapy treatments and to prevent sepsis.

The device is placed on the patient's fingertip, in a similar way to how pulse oximeters are used in hospitals to measure blood oxygen levels. With a small lens, the system captures images of capillaries very close to the surface in the nailbed. When illuminating at certain frequencies, light is absorbed by the hemoglobin in the red cells, an effect that does not happen with the white cells. This means that the leukocytes appear as small transparent particles moving inside the capillary.

There are currently three different prototypes. One of them is a portable microscope which is placed manually on the patient's finger to take videos of their microcirculation in very superficial capillaries. This device has already been tested on 31 patients in a Spanish hospital and on six more in Massachusetts General Hospital. A second version of the prototype includes modifications to the microscope to improve the stability and quality of the images. The third one is a small optical piece which can be added to a mobile phone camera to obtain images of the circulation in the capillaries.

Carlos Castro-Gonzalez, PhD, a bioengineer, said, “The new device will allow white blood cells to be measured simply and painlessly. The same way diabetics nowadays have a glucometer to check their glucose levels; patients undergoing chemotherapy will be able to use a 'leukometer' in the future to estimate the state of their immune system. In rural areas where access to health centers is limited, or in developing countries, this becomes a huge advantage. It would also be possible to perform measurements on a continuous basis, opening up treatment options that were previously not possible.” The study was presented at the Annual International Conference of the IEEE Engineering in Medicine and Biology Society held during August 25–29, 2015, in Milan (Italy).

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