About five years ago, I decided to test that assumption. I ran an experiment to see if blood tests from the knee area were as accurate as those taken from the finger. My experiment consisted of 40 blood sugar tests, done in triplicate. The area just above the knee is an accurate, painless site for blood sugar testing. There are some problems with knee testing.
Women seem to have more trouble than men getting an accurate sample.
Skinny persons such as I am can get a fold of skin to squeeze it to milk a drop of blood to the surface easier than can persons whose skin is more tightly filled. Some meters do not allow the tester to invert the meter over the puncture site and touch the reaction pad to the drop of blood. As an inconvenience, there is sometimes the tendency for a bit of blood to ooze, after the test, and this may stain the knee of your trousers. Blood sampling from above the knee can provide an accurate and painless alternative to finger-stick blood glucose monitoring.