The pathology systems use a library of normal values of test parameters to trigger flags on results that are out of range. These are the same reference ranges that are listed in the pathology handbook for Biochemistry, Immunology and Haematology tests; they are becoming increasingly sophisticated as they can be linked to specific sex- or age- weighted ranges.
The same approach is difficult to adopt for microbiology reports, because much of the information contained in them is textual and interpretive rather than numeric. In many cases the clinical context of a result can determine whether a particular result is significant or not: the same organism which can be commensal in one setting may be a significant pathogen in others. Similarly the finding "_______ antibody detected" can be normal or abnormal depending on the circumstances. For these reasons it is not possible in microbiology reports to pre-define specific values which can be used to define 'abnormal'. The medical microbiologists review reports which may require interpretation and will add relevant comments when necessary, but it would not be safe to assume that no comment = not significant.