These are nontreponemal tests that measure IgG and IgM antibodies to lipoidal material released from damaged host cells as well as to lipids and lipoproteins produced by the treponems. Rapid Plasma Reagin Card (RPR) and Venereal Disease Research Laboratory (VDRL) tests are two examples of reagin tests used in the Serology Branch.

The VDRL tests are slide microflocculation tests that use an antigen containing cardiolipin, lecithin and cholesterol. The VDRL antigen forms flocculates when combined with lipoidal antibodies in cerebrospinal fluid from syphilis patients.

RPR Card test is a macroscopic nontreponemal flocculation test that uses a modified VDRL antigen suspension containing choline chloride to eliminate the need to heat inactivate serum, ethylenediaminetetraacetic acid (EDTA) to enhance the stability of the suspension, and finely divided charcoal particles as a visualizing agent. Patient sera and controls are reacted with the RPR antigen on a circle in the test card. If sera contains antilipoidal antibodies, aggregates of antigen-antibody will be seen in the test circle (Figure 1). A nonreactive result will show as a button of non-aggregated carbon particles in the center of the circle (Figure 2).