Extracorporeal blood treatment and system having reversible blood pumps

An extracorporeal blood treatment system comprising:

• a blood circuit comprising a first blood passage coupled to a blood filter and a second blood passage coupled to the blood filter, wherein said first and second blood passages each are adapted to be coupled to a vascular system of a human patient;
• at least one blood pump connectable to the first blood passage, wherein said pump is adapted to move blood through the first and second blood passages and the filter,
• a filtrate collection container configured to receive filtrate withdrawn from the filter,
• a single air-in-blood detector configured to simultaneously monitor both the first and second blood passages,
• a pump controller operatively connected to the blood pump to control a rate of blood withdrawal into the blood circuit wherein the single air-in-blood detector comprises a housing including a slot configured to receive two or more passages configured as flow passages for extracorporeal blood;
• a transmitter of wave energy in the housing and oriented to direct wave energy across the slot and through the two or more passages, and
• a receiver of wave energy in the housing and oriented to receive wave energy transmitted by the transmitter, and the receiver configured to generate a signal indicative of the received wave energy passing through the two or more passages.