What % of diverticulitis cases would have elevated inflammation markers in a blood test?

Depends: It depends on how much of the colon is involved. If there is an isolated diverticulum that is inflamed, it may not affect serum markers of inflammation. If the whole sigmoid colon is affected it would certainly increase inflammation markers. Not all markers are affected equally. The commonly used markers are Sed rate, C-reactive protein, pro-calcitonin and serum protein electrophoresis.