You can do it without blood: we found a new way to collect tests
Tissue fluid can be used for many medical tests. The advantage of such tests is that they are painless: they use patches with microneedles.
What is tissue fluid 
Tissue fluid surrounds the cells of the body, it comes out of small blood vessels. This fluid is needed to transfer nutrients to the tissues and remove metabolic products from them. From the intercellular space, the fluid enters the lymphatic capillaries and returns to the blood, writes Science Translational Medicine.
Diagnostics using tissue fluid
The authors of the new study indicate that tissue fluid contains biomarkers that can be used in diagnostics. However, it is not used for this purpose, since there are no available methods for collecting it.
American scientists have developed a patch with microneedles that makes small holes in the skin and can collect tissue fluid for analysis. Previously, such attempts were unsuccessful, because the liquid got an admixture of blood. The authors of the new study were able to cope with this problem.
Tissue fluid instead of blood
In the study, researchers collected tissue fluid from a 
person. They compared the results of her tests with the results of blood tests. The samples had similar levels of many clinically important substances, including glucose, caffeine, and vitamin D.
Microneedles are much smaller than regular needles, they leave very small holes in the skin that can be tightened during the day.
Why is this important
Scientists emphasize that tissue fluid, unlike blood, does not form blood clots, so such a patch would be convenient to use for long-term monitoring of the level of certain biomarkers in the body. Currently, there is a method for long-term monitoring of blood glucose levels, but it requires the introduction of a subcutaneous sensor.
