Clinical Guide > Testing and Assessment > Laboratory Tests

Initial and Interim Laboratory and Other Tests

January 2011

Chapter Contents


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 a positive HIV serologic test result is essential for each patient, and it should be included in the patient's chart.

O: Objective

Table 1. Laboratory Evaluations for HIV-Infected Patients

TestRationaleResultFrequency and Comments
HIV Staging and ART Monitoring
CD4 Count
  • For HIV staging and prognosis
  • Helps guide initiation of ART
  • 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.
  • 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; must be confirmed by positive result on HIV antibody test (one viral load test is FDA approved for diagnosis of HIV)
  • 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 <50 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
Predicting Safety and Efficacy of ARVs
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 or for patients with detectable HIV RNA while taking ART.
  • Virologic failure: recommended.
  • Consider 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 be avoided
  • Test before making decision to treat with CCR5 antagonist, or if virologic failure occurs while on a CCR5 antagonist.
  • 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.
Baseline and Subsequent Hematologic, Renal, Hepatic, and Metabolic Screening
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.

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 every 3-6 months, and as needed.
  • 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 6 months in patients with HIV-associated nephropathy.
  • Repeat every 12 months (for patients on tenofovir, every 6 months); 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.
  • Repeat ≤3 months after starting or changing ART, annually if normal (on or off ART), or more frequently (every 3-6 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)
  • Detects diabetes and hyperglycemia
  • Normal/abnormal Baseline
Baseline; before starting ART.
  • Repeat every 3 months if abnormal, every 6 months if normal.
  • May influence ARV selection.
  • May be useful in monitoring drug toxicities.
See chapter Insulin Resistance, Hyperglycemia, and Diabetes on Antiretroviral Therapy.
Hepatitis A, B, and C Screening
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.
  • 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
Hepatitis C Antibody (HCV IgG)
  • Hepatitis C status
  • HCV negative
  • Patient is not infected with hepatitis C.
  • Consider annual screening for high-risk patients.
  • HCV positive
  • Patient has chronic hepatitis C infection or past infection with spontaneous clearance (no protective immunity); confirm positive results with HCV RNA.
Other Opportunistic Infection Screening Tests
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 when CD4 count drops to ≤100 cells/µL.
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 6-12 months.
  • Repeat TST if CD4 count was <200 cells/µL on initial TST but increases to >200 cells/µL.
  • Abnormal (TST induration ≥5 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: Follow-up interval has not been determined; consider same as in cervical Pap screening.
  • Abnormal
Pregnancy Screening
Pregnancy Test
  • Indicates pregnancy status
  • Positive/negative
Sexually Transmitted Infection Testing
(identify STIs in any patient at risk)
Serum VDRL (Venereal Disease Research Laboratory) or RPR (Rapid Plasma Reagin)
  • Syphilis screening
  • Negative/nonreactive
  • Repeat every 3-12 months, depending on risk factors.
  • Positive/reactive: confirm with treponemal test
  • Treat patient; refer partner(s) of previous 60 days for evaluation and treatment; counsel about safer sex.
  • Perform serial testing if monitoring active disease. (See chapter Syphilis.)
Gonorrhea (GC) and Chlamydia (CT) Testing Screen for STIs in sexually active women at risk; screen all at baseline; frequency of subsequent testing depends on risk factors Screen all sites of possible exposures:
  • Pharynx (recommended for GC screening)
  • Cervix/vagina
  • Urethra
  • Rectum
  • Negative
  • Counsel about safer sex and avoiding STIs.
  • Repeat every 6-12 months; more frequently if at high risk.
  • Positive
  • Treat patient; refer partner(s) of previous 60 days for evaluation and treatment; counsel about safer sex.
Trichomoniasis Testing
  • Wet mount or culture of vaginal secretions
  • Negative
  • Counsel about safer sex and avoiding STIs.
  • Positive
  • Treat patient; refer partner(s) for evaluation and treatment; counsel about safer sex.
Gonorrhea (GC) and Chlamydia (CT) Testing
  • Screen for STIs in sexually active men who are at risk, especially men who have sex with men (MSM)
  • Screen all at baseline; frequency of subsequent testing depends on risk factors
  • Screen sites of possible exposures:
    • Pharynx (recommended for GC screening)
    • Rectum
    • Urethra (consider for MSM with history of unprotected insertive intercourse in preceding year)
  • Negative
  • Retest every 3-6 months for patients with risk factors.
  • Positive
  • Treat; refer partner(s) of previous 60 days for evaluation and treatment; counsel about safer sex.
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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