Tests
1st tests to order
HIV antigen/antibody blood test (blood ELISA or EIA)
Test
Fourth-generation antigen/antibody tests are recommended.
Antibody testing alone is an alternative if antigen/antibody test unavailable.
All patients starting post-exposure prophylaxis (PEP) should have a baseline HIV enzyme-linked immunosorbent assay (ELISA) or enzyme immunoassay (EIA) test, but the 45-day window period (false-negative) should be considered.
A positive result should be confirmed with a second HIV ELISA, EIA, or a Western blot test and a referral made to the local HIV clinic. If the patient has already started PEP before the HIV diagnosis, PEP should be continued until review by an HIV specialist. A negative result should be followed up by repeating the HIV test after completion of PEP. The recommended schedule for follow-up testing differs between guidelines.[3][4]
If a patient tests positive at any time, they should be referred to a specialist HIV center.
Result
may be negative or positive
rapid HIV point of care test (POCT)
Test
Antigen/antibody (Ag/Ab) testing (or antibody testing if Ag/Ab test unavailable).
A baseline rapid POCT HIV test should be offered to all patients receiving post-exposure prophylaxis (PEP). Negative result may occur if the patient is within the window period. There is a possibility of false-positive result in low-prevalence populations.[56] A serum HIV test should be sent at the same time.
A positive test should be confirmed with a serum HIV test, and PEP should not be started in these cases.
Result
may be negative or positive
renal function tests
Test
Renal function should be performed at baseline and as part of post-exposure prophylaxis monitoring at 2 and 4 weeks.
Serum creatinine plus urinalysis or urine protein:creatinine ratio: if significant renal dysfunction or significant proteinuria present, avoid tenofovir disoproxil fumarate. Other antiretroviral medications may need dose adjustment.
Result
baseline assessment, may be normal or deranged
liver function tests (LFTs)
Test
Liver enzymes should be measured at baseline and as part of post-exposure prophylaxis (PEP) monitoring at 2 and 4 weeks. If abnormal at baseline or follow-up tests, consider testing for chronic viral hepatitis or syphilis and consider frequent monitoring once PEP initiated.
Result
may be normal; baseline abnormal LFTs may reflect chronic hepatitis B, chronic hepatitis C, or alcoholism
hepatitis B serology
Test
Hepatitis B surface antigen and core antibody should be done to determine chronic infection, and hepatitis B surface antibody to determine immunity from prior vaccination. May be negative, but can also show immunity or current infection. If negative or no history of vaccination, hepatitis B vaccination should be considered with the possible addition of hepatitis B immune globulin (HBIG) if the source is known to have hepatitis B or is high risk for hepatitis B. If acute or chronic infection, will need further follow-up and referral to a hepatologist. If chronically infected with hepatitis B, this would impact choice of antiretrovirals as many medications active against hepatitis B are also active against HIV and must be carefully chosen with the assistance of an infectious disease specialist.
Result
positive in hepatitis B-infected patients
hepatitis C antibody
Test
Where the index case is at high risk for hepatitis C infection (e.g., a person who injects drugs), a hepatitis C polymerase chain reaction or core antigen should be performed. If positive, refer for specialist hepatitis management.
Result
antibody positive in hepatitis C-infected patients
syphilis serology
Test
If positive, detailed history including previous syphilis tests, diagnoses, or treatment in conjunction with serology may help identify whether it is early or late syphilis and guide management. Patients with positive serology may require referral to specialist services for treatment.
All patients on post-exposure prophylaxis need repeat syphilis rapid plasma reagin or Venereal Disease Research Laboratory testing at 1 and 3 months.
Result
positive in patients with syphilis infection
pregnancy test
Test
Whether or not exposure was unprotected receptive vaginal intercourse, pregnancy test should be done in women considering post-exposure prophylaxis, and repeated as appropriate.
Result
may be negative or positive
screening for other STIs
Test
Chlamydia and gonorrhea screening should be offered if there were other sexual exposures prior to the current episode. However, the window period for these tests should be considered, and repeat screening should be offered 4 weeks after sexual exposure. If positive, refer patient for treatment.[49]
Result
may be negative or positive
Tests to consider
HIV viral load if symptoms of HIV seroconversion
Test
Mononucleosis-like or flu-like illness with fever, sore throat, rash, diarrhea, or other symptoms may occur with acute HIV infection (consistent with primary HIV infection). This may occur up to 12 weeks after exposure. Under this circumstance, HIV antibody testing may be negative but an elevated viral load or 4th-generation HIV-antigen/antibody test will confirm the diagnosis. Viral load testing is not routinely done unless acute HIV infection is suspected.[54][55]
Result
elevated in primary HIV infection
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