Nontreponemal tests for syphilis

A nontreponemal test (NTT) is a blood test for diagnosis of infection with syphilis. Nontreponemal tests are an indirect method in that they detect biomarkers that are released during cellular damage that occurs from the syphilis spirochete. In contrast, treponemal tests look for antibodies that are a direct result of the infection thus, anti-treponeme IgG, IgM and to a lesser degree IgA. Nontreponemal tests are screening tests, very rapid and relatively simple, but need to be confirmed by treponemal tests.^[1] Centers for Disease Control and Prevention (CDC)-approved standard tests include the VDRL test (a slide test), the rapid plasma reagin (RPR) test (a card test), the unheated serum reagin (USR) test, and the toluidine red unheated serum test (TRUST).^[2] These have mostly replaced the first nontreponemal test, the Wassermann test.

Syphilitic infection leads to the production of nonspecific antibodies that react to cardiolipin. This reaction is the foundation of “nontreponemal” assays such as the VDRL (Venereal Disease Research Laboratory) test and Rapid Plasma Reagin (RPR) test. Both these test are flocculation type tests that use an antigen-antibody interaction. The complexes remain suspended in solution and therefore visible due to the lipid based antigens.^[3][4]

All nontreponemal tests measure immunoglobulins G (IgG) and M (IgM) anti-lipid antibodies formed by the host in response both to lipoidal material released from damaged host cells early in infection and to lipid from the cell surfaces of the treponeme itself.

These nontreponemal tests are widely used for qualitative syphilis screening. However, their usefulness is limited by decreased sensitivity in early primary syphilis and during late syphilis, when a large number of untreated patients will be negative by these methods.

非トレポネーマ検査では、多くの理由で偽陽性反応が起こる可能性があり、最も一般的なのはウイルス性および細菌性の他の感染症です。さらに、フック効果（プロゾーン効果とも呼ばれる）により患者の抗体価が非常に高い場合、これらの検査では偽陰性を示す可能性があります。偽陽性の問題があるため、梅毒トレポネーマ抗体に特異的な2回目のトレポネーマ検査で確認することが推奨されます。^{[ 5 ] [ 6 ]}

これらの検査は比較的簡単に実施および解釈でき、迅速な結果の返却が可能で、非常に安価です。ただし、検査を実施および解釈するには、いくつかの検査機器（特にVDRL）と訓練を受けた人員が必要です。^{[ 2 ]}