Investigations
1st investigations to order
fourth-generation antigen/antibody enzyme-linked immunosorbent assay (ELISA)
Test
A fourth-generation combined antigen/antibody immunoassay that detects HIV-1 and HIV-2 antibodies and the HIV-1 p24 antigen is the recommended initial test for people with potential HIV exposure or acquisition, and is recommended at entry into care.[78][93] No further testing is required for specimens that are negative (non-reactive) on the initial immunoassay. If the specimen is positive (reactive), an HIV-1/HIV-2 antibody differentiation test (multispot) is recommeded.[93]
Obtaining a diagnosis of HIV during the window period is more likely with the combined antigen/antibody test as it detects both HIV antibodies and the p24 antigen. This reduces the window period to an average of 10 days.[87]
Rapid tests may be used for initial testing in some clinical settings. Several rapid tests are available. Most of the tests detect HIV antibodies in blood (fingerstick) with high sensitivity and specificity when combined with confirmatory testing. False-negatives may occur during the window period immediately after infection before antibodies to HIV have occurred. A positive result should be confirmed with a second rapid test. The Determine® HIV-1/HIV-2 antigen/antibody combination test is the first rapid point-of-care fourth-generation test that provides testing from fingerstick, venipuncture, or plasma samples with results within 20 minutes.[105]
Result
positive
HIV-1/HIV-2 antibody differentiation immunoassay
Test
An HIV-1/HIV-2 antibody differentiation immunoassay (multispot) is recommended if the initial antigen/antibody immunoassay is positive (reactive). Reactive results on the initial antigen/antibody immunoassay and the HIV-1/HIV-2 antibody differentiation immunoassay should be interpreted as positive for HIV-1 antibodies, HIV-2 antibodies, or HIV antibodies (undifferentiated). If the result is non-reactive or indeterminate, an HIV nucleic acid test is recommended.[93]
Result
positive for HIV-1 antibodies; positive for HIV-2 antibodies; positive for HIV antibodies (undifferentiated)
HIV nucleic acid test
Test
An HIV nucleic acid test is recommended if there is a possibility of very early infection (e.g., when recent HIV exposure is suspected or reported), or if the HIV-1/HIV-2 antibody differentiation immunoassay is non-reactive, indeterminate, or discordant.[93]
Result
positive for HIV RNA
CD4 count
Test
Recommended at entry into care and prior to initiation of antiretroviral therapy (ART).[78] If ART is delayed, testing is recommended every 3 to 6 months. Monitored during treatment. Indicates immune status and assists in the staging process.
Result
CD4 count of >500 cells/microlitre: patients are usually asymptomatic; CD4 count of <350 cells/microlitre: implies substantial immune suppression; CD4 count <200 cells/microlitre: defines AIDS and places the patient at high risk of most opportunistic infections
serum viral load (HIV RNA)
Test
Recommended at entry into care and prior to initiation of antiretroviral therapy (ART). If ART is delayed, repeat viral load testing before initiation. Repeat testing is optional in patients not initiating treatment. Monitored during treatment.[78]
An important test for establishing a baseline viral load before therapy and monitoring response to ART. A baseline viral load followed by measurements at regular intervals is recommended, depending on the patient's response to therapy.[78]
HIV RNA levels in acute infection are generally very high (e.g., >100,000 copies/mL). However, levels may be <200 copies/mL in the earliest weeks following infection as viral load rises. In rare cases, levels <200 copies/mL in the setting of a negative or indeterminate antibody test result may represent a false-positive result. When a low positive quantitative HIV RNA test result is present at this level, the HIV RNA test should be repeated on a new blood specimen to confirm the diagnosis. Repeated false-positive test results are unlikely.[78]
Point of care viral load tests have been found to have high sensitivity and specificity for the diagnosis of high viral loads (≥1000 copies/mL) in people with HIV who attend healthcare facilities compared to central laboratory-based assays.[106]
Result
people with HIV who are recently infected may attain levels in the millions of copies/mL; viral loads increase again into millions at end stages of infection
drug resistance testing
Test
Recommended at entry into care and prior to initiation of antiretroviral therapy (ART) to help guide selection of initial regimen. If ART is deferred, repeat testing is optional and may be considered at the time of initiation.[78]
Testing is also recommended to assist the selection of ART when changing regimens in treatment-experienced patients with virological failure and HIV RNA levels >200 copies/mL (drug resistance testing may be unsuccessful in patients with HIV RNA levels between 200 and 500 copies/mL, but it should still be considered), or with suboptimal viral load reduction.[78]
Treatment should not be delayed while awaiting results, as the regimen can be modified once results are received.[78]
Standard genotype testing involves testing for mutations in the integrase, reverse transcriptase and protease genes. Testing is recommended while the patient is still taking the regimen, or within 4 weeks after discontinuing the regimen, for non-long-acting agents. For patients taking long-acting injectable drugs, testing is recommended regardless of the time since discontinuation.[78]
Genotypic testing is preferred over phenotypic testing to guide treatment in treatment-naive patients, or guide treatment in people with a suboptimal virological response or virological failure while on first- and second-line regimens. However, combined genotypic and phenotypic resistance testing is recommended for people with known or suspected complex drug-resistance mutation patterns.[78]
Tropism testing is recommended if considering a CCR5 antagonist.[78]
One Cochrane review found that drug resistance testing (genotypic or phenotypic) is likely to have little or no impact on mortality, progression to AIDS, or CD4 count. However, it may reduce the risk of virological failure and viral load in patients who are experiencing treatment failure. It is unclear whether the benefits of resistance testing may be greater for treatment-naive patients.[103]
Dried blood spot specimens may be used for drug resistance testing in some locations (e.g., low- and middle-income countries, rural or remote areas), as they don’t require special laboratory processing.[107]
Result
variable
pregnancy test
Test
Recommended at entry into care, prior to initiation of antiretroviral therapy (ART), or if clinically indicated.[78] Some drugs are not recommended in pregnancy. Urine beta human chorionic gonadotrophin (beta-hCG) is sufficient.
Result
positive in pregnant women
serum hepatitis B serology
Test
Recommended at entry into care and prior to initiation of antiretroviral therapy (ART) if switching to a regimen that does not contain tenofovir. Monitored during treatment if clinically indicated. Also recommended before starting direct-acting antiviral therapy for hepatitis C infection due to risk of hepatitis B reactivation.[78] If the result is negative, the patient should be vaccinated against hepatitis B.[91]
Result
surface antigen, antibody to hepatitis B surface antigen, and antibody to hepatitis B core antigen positive in patients with hepatitis B
serum hepatitis C serology
Test
Recommended at entry into care. Monitored during treatment in at-risk patients or if clinically indicated.[78]
Result
antibody positive in patients with hepatitis C
hepatitis A serology (IgG)
Test
Should be performed in all patients. If the result is negative, the patient should be vaccinated against hepatitis A.[91]
Result
may be negative or positive
toxoplasma serology (IgG)
Test
Should be performed at baseline in all individuals with HIV, particularly those with a CD4 count of <200 cells/microlitre.
If the result is positive and the CD4 count is <50 cells/microlitre, prophylactic therapy should be started.
Result
may be negative or positive
FBC with differential
Test
Order at entry into care and prior to initiation/modification of antiretroviral therapy (ART). Monitored during treatment.[78]
The overall prevalence of anaemia across studies was 7.2% to 84%, and the overall prevalence of thrombocytopenia was 4.5% to 26.2%. There is an increased risk in patients with CD4 count <200 cells/microlitre, increased viral load, and coinfections or opportunistic infections.[108]
Result
may be normal or show anaemia or thrombocytopenia
basic metabolic panel
Test
Order at entry into care and prior to initiation/modification of antiretroviral therapy (ART). Monitored during treatment.[78]
Result
electrolytes may be normal or deranged; creatinine may be normal or elevated in coexisting renal disease
urinalysis
Test
Order at entry into care. Monitored during treatment if clinically indicated.[78]
Result
may be normal or show proteinuria in renal disease or positive for leukocytes and nitrites in urinary tract infections
liver function tests (LFTs)
Test
Order at entry into care and prior to initiation/modification of antiretroviral therapy (ART). Monitored during treatment.[78]
Result
may be normal; baseline abnormal LFTs may reflect chronic hepatitis B, chronic hepatitis C, or alcoholism
random or fasting plasma glucose
Test
Order at entry into care and prior to initiation/modification of antiretroviral therapy (ART). Monitored during treatment if clinically indicated or treatment failure.[78]
Result
may be elevated in patients on ART
lipid profile
Test
Order at entry into care. Monitored during treatment.[78]
Result
cholesterol levels may be low at diagnosis; antiretroviral therapy (ART) may be associated with rising levels
human leukocyte antigen-B*5701 testing
]
testing for sexually transmitted infections (STIs) including mpox
Test
Order tests for STIs including gonorrhoea, chlamydia, syphilis, and mpox according to local protocols, regardless of reported risk. Guideline-directed treatment may be required.
Result
may be negative or positive
Investigations to consider
chest x-ray
Test
Order if there are symptoms or signs of tuberculosis (TB), P jirovecii pneumonia, or other pulmonary illness.[4][91]
Result
Pneumocystis jirovecii pneumonia: interstitial to extensive alveolar shadowing; TB: many abnormalities possible including apical fibrosis/scarring, pleural effusion, hilar adenopathy, miliary pattern, lobar or patchy opacification; bacterial pneumonia: lobar or patchy opacification
testing for tuberculosis
Test
Indicated to establish evidence of exposure to and infection with tuberculosis. Tuberculin skin test or an interferon-gamma release assay (IGRA) is recommended. Those with a positive test should be treated for latent tuberculosis after active tuberculosis has been ruled out.[91]
Result
may be negative or positive
testing for cryptococcosis
Test
Consider ordering serum cryptococcal antigen in patients with CD4 counts <100 cells/microlitre or symptomatic patients.[91] Serum serum cryptococcal polysaccharide antigen (CrAg) can be detected using rapid antigen tests.
Result
may be negative or positive
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