Method for checking the operating configuration of the arterial and venous lines of a blood treatment apparatus, the blood treatment apparatus including a blood treatment unit having a semi permeable membrane delimiting a first chamber through which blood removed from said blood access passes and a second chamber through which dialysis liquid passes, an arterial line connected to an inlet of the first chamber, anda venous line connected to an outlet of the first chamber, said arterial and venous lines being able to be configured according to at least a normal configuration, in which said arterial line carries blood from said upstream position of said blood access, and said venous line carries blood towards said downstream position of said blood access, and to at least a reversed configuration, in which said arterial line carries blood from said downstream position of said blood access, and said venous line carries blood towards said upstream portion of said blood access.
