False positive 51Cr release tests during post-transplant immunological monitoring due to recipient serum radioactive contamination.

The occurrence of false positive 51Cr release test results in post-transplant immunological monitoring of human kidney graft recipients due to 131I carryover from renograms is described. False positivity was detected in 7 instances in 4 recipients, and suspected in 12 instances in 7 recipients, in a series of 46 consecutive transplant recipients. Technical methods and controls to detect and prevent such false positivity are described.