Since there is no blood in the fluid, you can clearly see that the needle tip is not in the blood vessel.
the test is performed at each injection of the needle;
fixation of a hand with a syringe;
reverse movement of the piston, while the evaluation of the sample is carried out within 10 seconds;
in the absence of a positive test result, we perform zone corrections.

Why 10 seconds? Two main criteria are still important here - the diameter of the needle and the rheology of the filler. When working with dense HA preparations and a wide needle lumen - 25-27 G, the sample is evaluated within 3 to 8 seconds. When working with soft preparations and a needle diameter of 28, 30 G, the time interval should be 10 seconds.!!! Mismatch between needle size and filler density can lead to false negative results.
Unfortunately, many doctors and cosmetologists follow this opinion. And ..... complications.
Let's see why?