Final answer:
The determination of whether a substance is blood is best made by means of a preliminary color test such as the Kastle-Meyer color test, which uses the reduction method to detect the presence of blood.
Step-by-step explanation:
The determination of whether a substance is blood is best made by means of a preliminary color test such as the Kastle-Meyer color test, which uses the chemical reduction method to detect the presence of blood. The reduction method involves the reaction of blood with a color indicator, where the intensity of the color developed is directly proportional to the amount of reducing substances present in the blood, such as glucose. This method is relatively economical and widely used in diagnostic laboratories for blood glucose estimation.