Final answer:
The fourth step in the blood treatment and return process is returning the cleaned blood to the patient after it has been filtered during hemodialysis.
Step-by-step explanation:
The step 4 in the treatment termination/returning blood process after hemodialysis is returning the blood sample to the patient. This critical step involves the reinfusion of the patient's treated blood back into their bloodstream. During hemodialysis, blood is filtered to remove waste products and excess fluid from the body. Once this filtration is complete, it is vital to safely return the filtered blood to maintain the patient's circulatory volume and to ensure that they receive the full benefit of the dialysis treatment.