The principle of total bilirubin meter is direct photometry. It tests the color of blood plasma, and gets the concentration of total bilirubin by compare the color to calibrator.
The collected blood divide to 2 parts after centrifuge, the bottom part is blood cell, the up part is plasma. The measuring light is shine at 37mm from bottom, so the level of blood cell must be less than 37 mm from bottom. If it is higher than this level, all the result will be wrong.
The capillary has only about 4 mm out of the measuring holder when it is inserted into measuring well through. If capillary is inserted improperly, the result will be wrong.