Thanks Walter for sharing such an interesting case. PCH is definitely something I would investigate in this case, although the hemolysis at 4C is rather atypical in a case of a positive LD test. I would also check for drug induced hemolysis ( An eluate would be informative in this case). I couldn't understand why your NaCl tube test at 4C gave lysis as well... (this reminded me of a time when one of my coworkers were getting such weird reactions ....turns out she somehow was using DI water instead of blood bank saline!