Phenolphthalein is one of the most commonly used chemicals in the field and laboratory to indicate the presence of blood. Our pre-packaged kit contains all the reagents to conduct a presumptive blood test. This simple 4 step test is easy to use and is housed in a small plastic cup. An immediate pink color on the end of the swab indicates a presumptive positive for blood. 60 tests per kit. 2 year shelf life. 60 tests per kit. 2 year shelf life.