Serologic and intradermal tests for parasitic infections.
For years, the diagnosis of most parasitic diseases has depended upon the direct demonstration of the parasite or its cysts, eggs, or larvae in specimens. In some infections, direct demonstration of the causative agent or its stages is almost impossible. In such cases, indirect techniques, such as serologic methods, have been found to be more practical and sensitive than are direct methods. Most serologic methods have been devised to detect antibodies. Tests for the detection of antigen are just beginning to be utilized; however, the practicality and under what situations antigen detection tests can be used await further testing. The majority of the serum antibody tests employ a heterogeneous mixture of antigens. Antigens derived from whole adult or larval stages usually result in tests with poor specificity and/or sensitivity. The necessity for better purified and standardized antigens cannot be over emphasized. Although there have been many major advances in the serodiagnosis of parasitic infections, a major drawback to routine use of parasitic serologies is the lack of commercially available reliable test kits. For the diagnosis of most parasitic diseases, one must rely upon specialty laboratories or public health laboratories. Before any laboratory begins to offer parasitic test serologies, they should contact their local or state public health laboratory or the Parasitic Serologic Section of the Centers for Disease Control to determine the pros and cons of these tests. Information of this type should be used to inform the physician of the limitations of the test in the differential diagnosis.