Laboratory Tests for Diagnosis
AIDS, acquired immunodeficiency syndrome; CSF, cerebrospinal fluid; ELISA, enzyme-linked immunosorbent assay; HBV, hepatitis B virus; HIV, human immunodeficiency virus; HSV, herpes simplex virus; mRNA, messenger RNA; RT, reverse transcriptase; PCR, polymerase chain reaction.
5-1 Polymerase chain reaction (PCR). After heating and melting a DNA sample, specific DNA primer sequences find, bind, and define the sample to be amplified. After cooling, a heat-stable DNA polymerase amplifies the DNA. The cycle is repeated 20 to 30 times, amplifying the sequence 220-30 times. (Modified from Blair GE, Blair Zajdel ME: Biochem Educ 20:87-90, 1992. In Murray PR, Rosenthal KS, Pfaller MA: Medical Microbiology, 6th ed. Philadelphia, Mosby, 2009, Fig. 16-4.)
5-2 Ouchterlony test. In this double-immunodiffusion method, antigen and antibody diffuse from wells in a gel and form a precipitin line (Ag-Ab precipitate) within the zone of equivalence. Identity: If two antigens share a common epitope specific for the antibody, a single continuous V-shaped precipitin line forms. In this example, both antigens contain epitope 1. Nonidentity: If two antigens have no common epitope, two distinct precipitin lines that cross are produced. In this example, one antigen contains epitope 1, and the other contains epitope 2. Partial identity: If two antigens share one epitope but not another, a continuous line with a spur forms. In this example, the right antigen contains epitopes 1 and 2, whereas the left antigen contains only one of these epitopes.