Initial and Interim Laboratory and Other Tests


This chapter discusses the laboratory tests and other monitoring that should be performed for HIV-infected individuals. This involves testing for staging HIV infection, screening for comorbidities, establishing baselines before treatment with antiretroviral (ARV) medications, and monitoring responses to ARV therapy (ART).

Note that documentation of HIV infection by laboratory testing is essential for each patient, and it should be included in the patient's chart.

O: Objective

Laboratory Evaluations for HIV-Infected Patients

Table 1. HIV Confirmation, Staging and ART Monitoring
TestRationaleResultFrequency and Comments
HIV Antibody
  • Confirm diagnosis, if not documented previously
  • At entry to care
CD4 Count
  • For HIV staging and prognosis
  • Helps guide urgency of ART initiation
  • Indicates risk of opportunistic illnesses and guides initiation of prophylaxis against opportunistic infections
  • Used to monitor immune reconstitution during ART
  • Reported in cells/µL
  • Perform at baseline (twice).
  • Repeat every 3-6 months for stable patients on or off ART; may repeat every 6-12 months if stable and suppressed viral load.
  • Repeat if results are inconsistent with the clinical picture or with previous trends.
  • See chapter CD4 and Viral Load Monitoring.
CD4 Percentage
  • Used in addition to the absolute CD4 count for monitoring trends; may be discrepant with absolute CD4
  • Pneumocystis pneumonia prophylaxis is indicated for CD4 percentage <14% regardless of absolute count
CD4 Count (cells/µL)Expected CD4 Percentage
  • Usually obtained with absolute CD4 count.
Quantitative Plasma HIV RNA (HIV Viral Load)
  • Estimates level of HIV replication
  • Used to monitor effect of ART
  • May be used to identify acute HIV infection; has high sensitivity in setting of acute infection, when antibody may be negative
  • Reported in copies/mL
  • In untreated patients, detectable (with rare exceptions) and measured to the upper limit of detection (usually >500,000 copies/mL)
  • For patients taking ART, ideally suppressed to undetectable levels (usually <40 or <75 copies/mL)
  • Perform at baseline (twice).
  • For patients on new or modified ART regimen: perform 2-8 weeks after initiation or change in ART, then every 4-8 weeks until viral load is suppressed.
  • For patients on stable ART: perform every 3-4 months (if stable and viral load suppressed >2-3 years, consider every 6 months).
  • For patients not taking ART: perform every 3-6 months; more frequently if CD4 count is low.

Factors that may temporarily increase viral load:

  • Immunizations
  • Active infections
Table 2. Predicting Safety and Efficacy of ARVs
TestRationaleResultFrequency and Comments
Drug Resistance Testing (Genotype, Phenotype)
  • To assess whether the patient's HIV virus is likely to be resistant to specific ARV medications
  • Genotype: detects specific mutations to ARV medications
  • Phenotype: measures HIV viral replication in the presence of ARVs
  • Genotype is recommended for all ARV-naive patients. For greatest accuracy, should be done as early as possible in the course of HIV infection.
  • Acute or primary infection: recommended (genotype).
  • Chronic infection and treatment naive: recommended before initiation of ART. (genotype). If resistance test was performed at entry, consider repeat testing.
  • Pregnancy: recommended before initiation of ART (repeat if done earlier) or for patients with detectable HIV RNA while taking ART.
  • Virologic failure: recommended.
  • Obtain genotype for integrase mutations if integrase inhibitor resistance is a concern.

(See chapter Resistance Testing for more information.)

Coreceptor Tropism Test
  • Determine coreceptor tropism
  • If CXCR4-tropic (or dual/mixed tropic) virus is detected, CCR5 antagonist is not likely to be effective and should not be used
  • Test before making decision to treat with CCR5 antagonist, or if virologic failure occurs while on a CCR5 antagonist (phenotypic assay preferred).
  • For standard assay, HIV RNA must be >1,000 copies/mL (a proviral DNA test is available for samples with HIV RNA below limits of detection; has not been clinically validated).
  • Establish risk of hypersensitivity reaction to abacavir
  • If positive, high risk of abacavir hypersensitivity reaction; abacavir should not be used
  • Test before starting treatment with abacavir.
Table 3. Baseline and Subsequent Hematologic, Renal, Hepatic, and Metabolic Screening
TestRationaleResultFrequency and Comments
Complete Blood Count (CBC) with Differential and Platelets
  • Detects anemia, thrombocytopenia, leukopenia
  • Normal
  • Perform at baseline.
  • Repeat every 3-6 months.
  • Abnormal
  • Requires follow-up evaluation as indicated; may influence choice of ARVs.
  • Repeat more frequently if the patient's results are abnormal or if the patient is taking bone marrow suppressive drugs (including zidovudine).

Chemistry Profile

Electrolytes, Creatinine, eGFR (Estimated Glomerular Filtration Rate), Blood Urea Nitrogen

Liver Transaminases, Bilirubin (Total and Direct)

  • Detects electrolyte abnormalities, kidney disease, liver disease
  • Normal/abnormal
  • Perform at baseline; before starting ART.
  • Repeat 2-8 weeks after starting or modifying ART, then every 3-6 months if stable.
  • May influence ARV selection.
  • May be useful in monitoring drug toxicities.
  • Abnormalities should prompt evaluation of cause.
Urinalysis with Urine Protein and Creatinine
  • Used to screen for kidney disease
  • Normal/abnormal
  • Screen at baseline and before initiation or change of ART regimen.
  • Repeat every 12 months.
  • Repeat every 6 months for patients on tenofovir, more frequently if indicated.
  • Abnormalities should prompt evaluation of cause.

See chapter Renal Disease.

Lipid Profile (Total Cholesterol, LDL, HDL, Triglycerides); fasting
  • Detects dyslipidemia, identifies risk factors for cardiovascular disease
  • Normal/abnormal
  • Baseline; before starting ART.
  • Consider repeating 4-8 weeks months after starting or changing ART.
  • Repeat annually if normal (on or off ART), or more frequently (e.g., every 6 months) if abnormal or risk of cardiovascular disease.
  • May influence ARV selection.
  • May be useful in monitoring drug toxicities.

See chapter Dyslipidemia.

Glucose (preferably fasting) or hemoglobin A1C
  • Detects diabetes and hyperglycemia
  • Normal/abnormal
  • Baseline; before starting ART.
  • Repeat every 3-6 months if abnormal, every 6 months if normal on ART; every 12 months if normal and not on ART.
  • May influence ARV selection.
  • May be useful in monitoring drug toxicities.

See chapter Insulin Resistance, Hyperglycemia, and Diabetes on Antiretroviral Therapy.

Table 4. Hepatitis A, B, and C Screening
TestRationaleResultFrequency and Comments
Hepatitis A Serology
Hepatitis A Antibody (HAV IgG)
  • Screen for immunity to hepatitis A; vaccinate those not immune
  • Negative
  • Positive
  • Immune; no vaccine necessary.
Hepatitis B Serology (See chapter Hepatitis B Infection.)
Hepatitis B Surface Antigen (HBsAg)
  • Indicates active hepatitis B
  • sAg negative
  • Most likely, no chronic infection (may be falsely negative).
  • Vaccinate if HBsAb negative (not immune).
  • sAg positive
  • Indicates chronic or acute hepatitis B infection; requires further evaluation (check HBV DNA). (See chapter Hepatitis B Infection.)
Hepatitis B Core Antibody (Anti-HBc, IgG)
  • Indicates past infection or ongoing infection
  • Anti-HBc negative
  • The patient most likely has not been infected with hepatitis B; consider vaccination if HBsAb negative and HBsAg negative.
  • Anti-HBc positive
  • The patient most likely has been infected with hepatitis B; this test alone does not distinguish past exposure and active infection.
  • In rare cases, may be falsely negative in some patients with chronic infection.
  • If sAb negative and sAg negative, check HBV DNA to rule out active infection; vaccinate if HBV DNA is not detected.
  • If sAb is positive, patient is immune.
Hepatitis B Surface Antibody (Anti-HBs)
  • Indicates immunity status
  • Anti-HBs negative
  • The patient is not immune to hepatitis B; consider vaccination, unless patient has active hepatitis (sAg positive or HBV DNA positive).
  • Anti-HBs positive
  • The patient is immune to hepatitis B either by previous infection or by immunization; may be negative in acute hepatitis B infection.
Hepatitis C Serology (See chapter Hepatitis C Infection.)
Hepatitis C Antibody (HCV IgG)
  • Hepatitis C status
  • HCV negative
  • Patient is not infected with hepatitis C.
  • Screen at baseline; consider annual screening for high-risk patients, and if clinically indicated.
  • HCV positive
  • Patient has chronic hepatitis C infection or past infection with spontaneous clearance (no protective immunity); confirm positive results with HCV RNA.
Table 5. Other Opportunistic Infection Screening Tests
TestRationaleResultFrequency and Comments
Toxoplasma gondii IgG
  • Detects past exposure; if positive, patient has increased risk of developing CNS toxoplasmosis if CD4 count <100 cells/µL
  • Negative
  • Repeat if patient becomes symptomatic or when CD4 count drops to ≤100 cells/µL.
  • Positive
  • Note as baseline information.
  • Start toxoplasmosis prophylaxis if CD4 count drops to ≤100 cells/µ.

Tuberculosis (TB) Screening

TST (Tuberculin Skin Test) or IGRA (Interferon-Gamma Release Assay) (if no history of TB or positive TB screening test in the past)

  • Detects latent TB infection (LTBI)
  • Normal
  • Repeat every 12 months if high risk of repeated or ongoing exposure.
  • Repeat if CD4 count was <200 cells/µL on initial test but increases to >200 cells/µL on ART.
  • Abnormal (TST induration ≥mm or positive IGRA)
Chest X-Ray (if pulmonary symptoms are present or positive LTBI test)
  • Detects latent or active diseases
  • Normal
  • Repeat as indicated for pulmonary symptoms or positive LTBI test.
  • Abnormal
  • Evaluate for TB, PCP, or other pathology.
Papanicolaou Test (cervical for women; consider anal for women and men)
  • Detects abnormal cell changes, dysplasia
  • Normal
  • Cervical: Repeat in 6 months, then annually if negative on two tests and no ongoing risk factors.
  • Anal: No national guidelines; consider screen at baseline. Follow-up interval has not been determined; consider same as in cervical Pap screening.
  • Abnormal
Table 6. Pregnancy Screening
TestRationaleResultFrequency and Comments
Pregnancy Test
  • Indicates pregnancy status
  • Positive/negative
Table 7. Sexually Transmitted Disease Testing
TestRationaleResultFrequency and Comments

Serum VDRL (Venereal Disease Research Laboratory) or RPR (Rapid Plasma Reagin)

(some centers screen using a treponemal test)

  • Screen for syphilis at least annually in sexually active persons who are at risk; for men who have sex with men (MSM) with multiple partners: every 3-6 months
  • Negative/nonreactive
  • Counsel about safer sex and avoiding STDs.
  • Repeat every 3-12 months, depending on risk factors.
  • Positive/reactive: confirm with treponemal test
  • Treat patient; refer partner(s) for evaluation and treatment; counsel about safer sex. (See chapter Syphilis.)
  • Perform serial testing if monitoring active disease. (See chapter Syphilis.)
Gonorrhea (GC) and Chlamydia (CT) TestingScreen for STDs in sexually active women at risk according to CDC and USPSTF guidelines; screen all ≤25 years of age at baseline and at least annually; more frequently if risk factors

Screen all sites of possible exposures:

  • Pharynx (recommended for GC screening)
  • Cervix/vagina
  • Rectum
  • Negative
  • Counsel about safer sex and avoiding STDs.
  • Repeat every 6-12 months; more frequently if at high risk (e.g., adolescents).
  • Positive
  • Treat patient; refer partner(s) of previous 60 days for evaluation and treatment; counsel about safer sex.
  • Retest at 3 months.
Trichomoniasis Testing
  • Wet mount (insensitive), culture or nucleic acid amplification test (NAAT) of vaginal secretions
  • Screen HIV-infected women annually
  • Negative
  • Counsel about safer sex and avoiding STDs.
  • Repeat every 12 months.
  • Positive
  • Treat patient; refer partner(s) for evaluation and treatment; counsel about safer sex.
  • Retest at 3 months.
Gonorrhea (GC) and Chlamydia (CT) Testing
  • Screen for STDs in sexually active men who are at risk according to CDC guidelines, especially MSM
  • Screen all MSM at baseline and at least annually; frequency of subsequent testing depends on risk factors
  • Screen sites of possible exposures:
  • Pharynx, if receptive oral sex (recommended for GC screening)
  • Rectum, if receptive anal sex
  • Urethra for MSM, if insertive oral or anal sex
  • Negative
  • Counsel about safer sex and avoiding STDs.
  • Retest every 3-12 months, depending on risk factors.
  • Positive
  • Treat; refer partner(s) of previous 60 days for evaluation and treatment; counsel about safer sex.
  • Retest at 3 months.
Table 8. Consider/Optional
TestRationaleResultFrequency and Comments
G6PD Level
  • Prevent hemolytic reactions to certain medications by screening higher-risk patients (African, Mediterranean, Asian, Sephardic Jewish descent); some would recommend screening all patients
  • Normal range
  • No intervention is necessary beyond documentation.
  • Abnormal range
  • Avoid oxidant drugs such as dapsone, primaquine, and sulfonamides, if possible.
Cytomegalovirus (CMV) Antibody (anti-CMV IgG) (for those at low risk of CMV, especially those who are not MSM or injection drug users)
  • Detects exposure; may reveal future disease risk
  • Negative
  • Avoid exposure by practicing safer sex.
  • If blood transfusion is required, use CMV-negative or leukocyte-reduced blood.
  • Positive
  • Be aware of disease risk in advanced HIV infection, when CD4 count is <50 cells/µL.
Varicella zoster (Varicella IgG) (for those without history of chickenpox or shingles)
  • Detects exposure
  • Negative
  • Consider vaccination, if CD4 count is >200 cells/µL.
  • Positive
  • No intervention is necessary.
Dilated Retinal Examination
  • Detects CMV, ophthalmic toxoplasmosis, or HIV retinopathy
  • Normal
  • If CD4 count is >100 cells/µL, repeat annually.
  • If CD4 count is <50 cells/µL or symptoms of retinal changes are present, repeat every 6 months.
  • Abnormal
  • Follow up immediately with ophthalmologist.

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