Surgical blood test. Image 1 of 2. Surgeon's hand holding a microcuvette containing a drop of blood. This will be inserted into a blood testing machine that will test for blood levels of haemoglobin, an essential blood chemical that transports oxygen around the body. The levels of haemoglobin must be monitored during surgery to prevent excessive loss due to bleeding. The microcuvette is brought into contact with the blood sample, and the required amount of blood is absorbed into the microcuvette by capillary action. This equipment is part of the HemoCue photometer range of testing equipment. For an image of the result of the test, see M550/689.