HIV Testing (4th Generation Algorithm)
Narrower "window period" (~14 days) by detecting p24 Antigen in addition to antibodies.
Step 1: HIV-1/2 Ag/Ab Combo Screen
(-) Non-reactive: Negative
(+) Reactive: Reflex to Step 2
Step 2: HIV-1/2 Antibody Differentiation
HIV-1 (+): HIV-1 Infection
HIV-2 (+): HIV-2 Infection
(-/Indeterminate): Reflex to Step 3 (NAT)
Hepatitis B Virus (HBV) Serology
| Status | HBsAg | HBsAb | HBcAb | IgM HBc |
|---|---|---|---|---|
| Acute Infection | + | - | + | + |
| Chronic Infection | + | - | + | - |
| Immune (Vaccine) | - | + | - | - |
| Immune (Natural) | - | + | + | - |
Hepatitis C Virus (HCV)
1. HCV Ab Screen
(+) Reactive: Reflex to HCV RNA
2. HCV RNA (PCR)
(+) Reactive: Active Infection (Treat)
(-) Non-reactive: Resolved or False Positive
Syphilis Testing Algorithms
Traditional
RPR Screen → Treponemal Confirm
Reverse
Treponemal Screen → RPR Reflex
Lyme Disease
Two-tiered testing is crucial to avoid false positives.
Screen: Lyme Ab (IgG/IgM) EIA
(+) Reactive: Reflex to Western Blot
CDC Criteria
IgM: 2 of 3 bands (valid symptomatic <30 days)
IgG: 5 of 10 bands