Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1427 page)

   Direct diagnostic value in scarlet fever, erysipelas, and streptococcal pharyngitis and tonsillitis. Indirect diagnostic value in RF, GN, detection of subclinical streptococcal infection, and differential diagnosis of joint pains of RF and RA.

   Interpretation

   Increased in pyoderma, postimpetigo nephritis caused by GAS, RF, and pharyngitis.

   Limitations

   When evaluating patients with acute RF, the American Heart Association recommends the ASO titer rather than ADB. Even though the ADB is more sensitive than ASO, its results are too variable. It also should be noted that, although ASO is the recommended test, when ASO and ADB are done together, the combination is better than either ASO or ADB alone.

   With the ASO test, false-positive results are observed with increased levels of serum beta lipoproteins produced in liver disease and contamination of serum with
Bacillus cereus
or
Pseudomonas
species. In addition, these titers are not formed as a result of streptococcal pyoderma. Technically, false-positive results occur due to the oxidation of reagents.

   A single ASO analysis may not be meaningful due to the variability of ASO values within the normal population. Both clinical and laboratory findings should be considered in reaching a diagnosis.

   Streptococcal infections already treated with antibiotics may not produce increased results.

SYPHILIS SEROLOGY TESTS

   Definition

   Syphilis is an STD caused by the bacterium
Treponema pallidum
. Symptoms of infection are often subtle and easily confused with other STDs such as genital herpes infection. Syphilis is passed from person to person through direct contact with infectious exudates from obvious or concealed, moist, early lesions of skin and mucous membranes of infected people during sexual contacts. Exposure almost always occurs during oral, anal, or vaginal intercourse. A pregnant woman with the disease can pass it to her newborn child.

   The diagnosis of syphilis is most commonly made by serologic testing and is typically performed in two settings: screening of patients at increased risk and evaluation of patients with suspected disease.

   There are two types of serologic tests for syphilis: nontreponemal tests such as the rapid plasma reagin (RPR) test and Venereal Disease Research Laboratory (VDRL) test, and specific treponemal tests such as the
Treponema pallidum
particle agglutination assay (TP-PA), fluorescent treponemal antibody absorption (FTA-ABS) test, and the microhemagglutination test for antibodies to
Treponema pallidum
(MHA-TP).