Abstract: Several tests are described for verifying the integrity of the extracorporeal circuit of a medical instrument, such as a dialysis machine. One test verifies the condition of the blood tubing set. Another test verifies that the clamps in the arterial and venous lines adequately occlude the arterial and venous lines. Another test confirms that the arterial and venous lines are properly installed on their respective ports for receiving the lines after the treatment session has ended. In this last test, a fluid such as heated water is then introduced into one of the arterial or venous lines and sent out of the line through its respective port, where it is detected with suitable fluid detection equipment such as a thermistor. The heated fluid and thermistor verify that the arterial line is connected to its arterial port and the venous line is connected to its venous port and that there is an unobstructed fluid path in the blood tubing set.