{ "id": "epmpaav12g", "slug": "viral-load-testing", "title": "Viral load testing", "updated": "2026-10-15", "topic_path": [ { "id": "life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/topics/life" }, { "id": "life.health", "label": "Human health and medicine", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health" }, { "id": "life.health.clinical", "label": "Clinical assessment and procedures", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.clinical" }, { "id": "life.health.clinical.clinical-diagnostics", "label": "Diagnosis and clinical assessment", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.clinical.clinical-diagnostics" }, { "id": "life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics", "label": "Laboratory and in-vitro diagnostics", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics" }, { "id": "life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics.antimicrobial-susceptibility-testing", "label": "Antimicrobial susceptibility testing", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics.antimicrobial-susceptibility-testing" } ], "geo": [ { "id": "geo.nongeo.t1946.life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics", "label": "Non-geographic · 1946 to 2000: Laboratory and in-vitro diagnostics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1946", "label": "Non-geographic · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946" }, { "id": "geo.nongeo.t1946.life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life" }, { "id": "geo.nongeo.t1946.life.health", "label": "Human health and medicine", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health" }, { "id": "geo.nongeo.t1946.life.health.clinical", "label": "Clinical assessment and procedures", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical" }, { "id": "geo.nongeo.t1946.life.health.clinical.clinical-diagnostics", "label": "Diagnosis and clinical assessment", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical.clinical-diagnostics" }, { "id": "geo.nongeo.t1946.life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics", "label": "Laboratory and in-vitro diagnostics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics" } ] } ], "excerpt": "Viral load testing measures the amount of virus in a patient's blood, reported as RNA or DNA copies per milliliter, to track infection and treatment response.", "snippet": "Viral load testing measures the amount of virus in a patient's blood, reported as RNA or DNA copies per milliliter, to track infection and treatment response.", "node": "life.health.clinical.clinical-diagnostics.laboratory-and-in-vitro-diagnostics.antimicrobial-susceptibility-testing", "markdown": "# Viral load testing\n\nViral load testing is a laboratory diagnostic method that measures the quantity of a virus's genetic material in a patient's blood to track infection activity and treatment response. Results are reported as RNA or DNA copies per milliliter or international units per milliliter. It is a nucleic acid amplification test (NAT): the test detects and quantifies viral genomes rather than antibodies or antigens.[1](https://medlineplus.gov/lab-tests/hiv-viral-load/) Quantitative NAT grew from a research tool to a clinically routine test in the mid-1990s and is now central to managing HIV, hepatitis C, and cytomegalovirus infections, where treatment decisions are written directly in viral load thresholds.[2](https://clsjournal.ascls.org/content/ascls/18/4/263.full.pdf)\n\n| Key fact | Detail |\n|---|---|\n| What is measured | Viral RNA or DNA in plasma or serum, reported as copies/mL or IU/mL, or as \\( \\log_{10} \\) values[3](https://www.ncbi.nlm.nih.gov/books/NBK558500/) |\n| Core technologies | Target amplification (RT-PCR, NASBA, TMA) and signal amplification (bDNA)[2](https://clsjournal.ascls.org/content/ascls/18/4/263.full.pdf) |\n| HIV-1 assay limits | FDA-approved real-time PCR assays quantify 20 to 10,000,000 copies/mL[3](https://www.ncbi.nlm.nih.gov/books/NBK558500/) |\n| HIV suppression | Confirmed HIV RNA below the assay limit, generally <20 copies/mL; failure defined as inability to reach or hold <200 copies/mL[4](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-arv/plasma-hiv-1-rna-cd4-monitoring) |\n| WHO failure threshold | Persistent viral load >1000 copies/mL after at least 6 months of ART[5](http://files.icap.columbia.edu/files/uploads/VL-SOP__Revised_July_2016.pdf) |\n| HCV test of cure | Assays detecting down to 1000 IU/mL suffice for cure assessment[6](https://iris.who.int/server/api/core/bitstreams/f5baa329-69a6-4142-945f-9d7ba27fbc40/content) |\n| Sample rule | EDTA plasma, never heparin tubes, which inhibit PCR[5](http://files.icap.columbia.edu/files/uploads/VL-SOP__Revised_July_2016.pdf) |\n\n## How it works\n\nAll viral load assays extract or access viral nucleic acid from a measured plasma volume and generate a measurable signal proportional to the amount of virus. Two amplification principles are used. Target amplification copies the viral genome enzymatically: reverse-transcription PCR (RT-PCR) converts RNA to DNA and amplifies it in thermal cycles; [nucleic acid sequence-based amplification](https://www.edgepedia.org/nucleic-acid-sequence-based-amplification) (NASBA) is an isothermal reaction (40 to 41 °C) using AMV reverse transcriptase, [T7 RNA polymerase](https://www.edgepedia.org/t7-rna-polymerase), and RNase H; transcription-mediated amplification (TMA) is a related isothermal RNA-amplification chemistry.[2](https://clsjournal.ascls.org/content/ascls/18/4/263.full.pdf) [Signal amplification](https://www.edgepedia.org/signal-amplification), used in branched DNA (bDNA) assays, captures viral particles with probes and attaches alkaline phosphatase-labeled oligonucleotides to branched structures detected by chemiluminescence; no enzymatic copying of the target occurs, so the signal is directly proportional to viral load and the measurement is less affected by the sample matrix.[7](https://doi.org/10.1097/00002030-199311002-00004)\n\nIn real-time PCR, quantification comes from the cycle threshold (Ct), the cycle at which fluorescence crosses a threshold. For the COBAS AmpliPrep/COBAS TaqMan HCV test, a 10-fold increase in titer corresponds to a 3.3-cycle decrease in Ct.[8](https://www.accessdata.fda.gov/cdrh_docs/pdf6/P060030c.pdf) Results are calibrated against standards and reported in copies/mL or IU/mL. International units come from WHO International Standards: the HCV test is standardized against the First WHO International Standard for HCV RNA (NIBSC 96/790),[8](https://www.accessdata.fda.gov/cdrh_docs/pdf6/P060030c.pdf) and the Abbott RealTime HIV-1 assay uses the WHO 1st International Standard for HIV-1 RNA (97/656), with a conversion of 1 IU = 0.58 copies.[9](https://www.molecular.abbott/content/dam/add/molecular/products/pdf-/realtime-hiv-1-package-insert.pdf) For cytomegalovirus, no overall copies-to-IU conversion exists; any conversion is restricted to an individual assay calibrated to the WHO standard (NIBSC 09/162).[10](https://www.sciencedirect.com/science/article/pii/S1045105616300070) Because results span orders of magnitude, clinicians express changes in \\( \\log_{10} \\) units: a 1-log change is a 10-fold change.[5](http://files.icap.columbia.edu/files/uploads/VL-SOP__Revised_July_2016.pdf)\n\n## How it is done\n\nThe pre-analytical phase determines result quality. Blood is collected in EDTA tubes; heparin tubes must not be used because heparin inhibits PCR.[5](http://files.icap.columbia.edu/files/uploads/VL-SOP__Revised_July_2016.pdf) Plasma is separated by centrifugation within 24 hours of collection and stored cold, at 2 to 8 °C for up to 6 days or frozen for longer periods.[11](https://www.publichealthontario.ca/en/laboratory-services/test-information-index/hiv-viral-load)\n\nAnalytically, an automated platform extracts nucleic acid, amplifies the target, and detects products with sequence-specific probes. The cobas HIV-1 assay amplifies the gag gene and LTR region and quantifies HIV-1 RNA from the ratio of target-probe to internal armored-RNA-standard fluorescence, over a range of 20 to 10,000,000 copies/mL.[12](https://www.mayocliniclabs.com/test-catalog/overview/113581) An internal control in each reaction monitors extraction and inhibition.[13](https://www.molecular.abbott/content/dam/add/molecular/products/infectious-disease/realtime-hcv-viral-load/realtime-hcv-package-insert.pdf) Turnaround is typically days: Public Health Ontario reports up to 6 business days for HIV-1 viral load.[11](https://www.publichealthontario.ca/en/laboratory-services/test-information-index/hiv-viral-load)\n\nInterpretation uses log changes and repeat testing. The minimal statistically significant change in HIV viral load is threefold (\\( 0.5 \\log_{10} \\) copies/mL) by NIH guidance.[4](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-arv/plasma-hiv-1-rna-cd4-monitoring) Monitoring schedules for HIV are viral load measured at ART initiation, within 4 to 8 weeks, every 4 to 8 weeks until suppression, then every 3 to 4 months, extendable to 6 months after a year of suppression.[4](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-arv/plasma-hiv-1-rna-cd4-monitoring)\n\n## Origin\n\nQuantitative plasma HIV-1 RNA measurement was reported in 1993 by more than one group. Direct, quantitative detection of HIV-1 RNA in plasma can be performed with a branched DNA signal amplification assay.[7](https://doi.org/10.1097/00002030-199311002-00004) The same year, van Gemen and colleagues reported qualitative and quantitative detection of HIV-1 RNA by nucleic acid sequence-based amplification in AIDS.[14](https://doi.org/10.1097/00002030-199311002-00020) In 1996, Kern and colleagues published an enhanced-sensitivity bDNA assay for HIV-1 RNA quantification in the Journal of Clinical Microbiology,[15](https://doi.org/10.1128/jcm.34.12.3196-3202.1996) and Mellors and colleagues showed in [Science](https://www.edgepedia.org/science-journal) that the quantity of virus in plasma predicted prognosis in HIV-1 infection, establishing viral load as a prognostic marker.[16](https://doi.org/10.1126/science.272.5265.1167) The first bDNA test measured down to 10,000 copies/mL; current assays detect as few as 20 copies/mL.[17](https://www.aidsinfonet.org/fact_sheets/view/125)\n\n## Variants\n\nHIV-1: FDA-approved quantitative assays include real-time PCR platforms with lower limits of quantification of 20 to 40 copies/mL and upper limits of 10,000,000 copies/mL, as well as the TMA-based Aptima HIV-1 Quant Dx assay, which reports a lower limit of quantification of 30 copies/mL and can detect HIV-1 RNA as low as 12 copies/mL in plasma.[3](https://www.ncbi.nlm.nih.gov/books/NBK558500/) Named platforms include Abbott RealTime HIV-1 on the m2000 system,[9](https://www.molecular.abbott/content/dam/add/molecular/products/pdf-/realtime-hiv-1-package-insert.pdf) Roche cobas HIV-1 on cobas 5800/6800/8800,[18](https://elabdoc-prod.roche.com/eLD/api/downloads/bc02acf5-7b3c-ee11-1f91-005056a772fd?countryIsoCode=XG) the Cepheid Xpert HIV-1 viral load plasma assay, and the Versant bDNA assay.[19](https://www.nature.com/articles/s41598-025-92709-y) The NucliSens EasyQ (bioMérieux, NASBA-based) is the only assay reporting results in IU/mL.[20](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0085869)\n\nHCV: the COBAS AmpliPrep/COBAS TaqMan test quantifies genotypes 1 to 6 in plasma or serum,[8](https://www.accessdata.fda.gov/cdrh_docs/pdf6/P060030c.pdf) Abbott RealTime HCV targets the conserved 5′UTR,[13](https://www.molecular.abbott/content/dam/add/molecular/products/infectious-disease/realtime-hcv-viral-load/realtime-hcv-package-insert.pdf) and cobas HCV uses two non-overlapping probes with staggered primers to tolerate sequence heterogeneity.[21](https://diagnostics.roche.com/content/dam/diagnostics/Blueprint/en/pdf/rmd/RMD_cobas-HCV-for-cobas-68008800.pdf) WHO has prequalified the Xpert HCV Viral Load (Cepheid) as a point-of-care HCV RNA assay.[6](https://iris.who.int/server/api/core/bitstreams/f5baa329-69a6-4142-945f-9d7ba27fbc40/content)\n\nCMV: FDA-cleared platforms include Cobas AmpliPrep/Cobas TaqMan CMV (Roche), Artus CMV RGQ MDx (Qiagen), and Abbott RealTime CMV.[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC9235525/) The Aptima CMV Quant assay (Hologic), a real-time TMA assay on the Panther system targeting the UL56 gene, received FDA approval in 2022 with a 95% limit of detection of 32 IU/mL.[23](https://pmc.ncbi.nlm.nih.gov/articles/PMC9945493/)\n\n## Applications\n\nHIV: optimal suppression is a confirmed HIV RNA below the assay's lower limit of detection, generally <20 copies/mL.[4](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-arv/plasma-hiv-1-rna-cd4-monitoring) NIH guidelines define virologic failure as inability to achieve or maintain HIV RNA <200 copies/mL, a threshold chosen to exclude most blips and assay variability.[4](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-arv/plasma-hiv-1-rna-cd4-monitoring) WHO defines virologic treatment failure as a persistent viral load exceeding 1000 copies/mL after at least 6 months of ART, with persistence meaning two consecutive measurements 3 to 6 months apart and adherence support between them.[5](http://files.icap.columbia.edu/files/uploads/VL-SOP__Revised_July_2016.pdf) Patients with viral load <200 copies/mL are considered virally suppressed and unlikely to transmit HIV (the U=U position).[11](https://www.publichealthontario.ca/en/laboratory-services/test-information-index/hiv-viral-load)\n\nHCV: WHO recommends reflex HCV RNA testing on every positive antibody test using the same specimen.[6](https://iris.who.int/server/api/core/bitstreams/f5baa329-69a6-4142-945f-9d7ba27fbc40/content) For test of cure, technologies detecting down to 1000 IU/mL are sufficient because most treatment failures have viremia above that level.[6](https://iris.who.int/server/api/core/bitstreams/f5baa329-69a6-4142-945f-9d7ba27fbc40/content) WHO's 2022 conditional recommendation allows point-of-care HCV RNA NAT assays to replace laboratory-based assays to diagnose viremic infection.[6](https://iris.who.int/server/api/core/bitstreams/f5baa329-69a6-4142-945f-9d7ba27fbc40/content)\n\nCMV in transplant recipients: quantitative NAT is the preferred assay for diagnosing infection, guiding preemptive treatment, and monitoring therapy response. Refractory infection is defined as CMV viremia that either increases (a \\( >1 \\log_{10} \\) increase in CMV DNA from the peak viral load) or persists (\\( \\leq 1 \\log_{10} \\) increase or decrease) after at least 2 weeks of appropriate antiviral therapy.[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC9235525/)\n\n## Limitations and alternatives\n\nSpurious results and blips: isolated blips of 50 to 500 copies/mL after suppression reflect random biologic or statistical variation or laboratory-processing artifacts, are not associated with resistance or failure, and are distinguished from sustained viremia by retesting within 4 weeks; consecutive blips, unlike isolated ones, have been associated with elevated risk of treatment failure.[3](https://www.ncbi.nlm.nih.gov/books/NBK558500/) • [24](https://www.hivguidelines.org/wp-content/uploads/2025/10/NYSDOH-AI-Virologic-and-Immunologic-Monitoring_3-31-2026_HG.pdf) Improper processing can inflate results: the cobas assay can amplify proviral DNA from white cells in the buffy coat if specimens are not properly centrifuged.[11](https://www.publichealthontario.ca/en/laboratory-services/test-information-index/hiv-viral-load) Concurrent infection or recent immunization can also elevate results.[17](https://www.aidsinfonet.org/fact_sheets/view/125)\n\nPrimer and probe mismatch: the Roche TaqMan v1 HIV-1 assay's primers failed to amplify efficiently in about 2.4% of samples, causing systematic underestimation by up to \\( 2.5 \\log_{10} \\) copies/mL.[25](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0043882) Commercial HIV-1 RNA assays do not detect HIV-2 viral load,[4](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-arv/plasma-hiv-1-rna-cd4-monitoring) and the cobas HIV-1 assay is unreliable for group N and may give discordant group O results.[12](https://www.mayocliniclabs.com/test-catalog/overview/113581)\n\nInter-assay variability: a systematic review of 37 studies found all available HIV assays reliably detect 1000 copies/mL, the WHO failure threshold, but bias between assays was substantial.[20](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0085869) Even with WHO-standard calibration, CMV assays show clinically relevant variability from platform, gene target, and amplicon differences, so serial monitoring should use the same platform and sample type.[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC9235525/) Results from different laboratories and test types can be difficult to compare.[1](https://medlineplus.gov/lab-tests/hiv-viral-load/)\n\nAlternatives: serologic and antigen tests establish that infection exists; viral load tests detect infection sooner than antibody tests but cost more, so they serve for diagnosis mainly when risk is very high.[1](https://medlineplus.gov/lab-tests/hiv-viral-load/) [Digital PCR](https://www.edgepedia.org/digital-pcr) matched expected copy numbers more closely than qPCR on titrated standards and had smaller inter-run coefficients of variation at low copy numbers, but produced more false-positive reactions on negative controls.[26](https://www.nature.com/articles/s41598-022-07196-2)\n\n## References\n\n1. [HIV Viral Load: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/hiv-viral-load/)\n2. [Molecular-based Laboratory Testing and Monitoring for Human Immunodeficiency Virus Infections (Clinical Laboratory Science, 2005)](https://clsjournal.ascls.org/content/ascls/18/4/263.full.pdf)\n3. [Virologic and Immunologic Monitoring in HIV Care - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK558500/)\n4. [Laboratory Testing: Plasma HIV-1 RNA (Viral Load) and CD4 Count Monitoring | NIH](https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-arv/plasma-hiv-1-rna-cd4-monitoring)\n5. [Viral Load Monitoring SOP (ICAP Columbia)](http://files.icap.columbia.edu/files/uploads/VL-SOP__Revised_July_2016.pdf)\n6. [Simplified service delivery and diagnostics for hepatitis C infection (WHO policy brief)](https://iris.who.int/server/api/core/bitstreams/f5baa329-69a6-4142-945f-9d7ba27fbc40/content)\n7. [Mickey S. Urdea and colleagues (1993). Direct and quantitative detection of HIV-1 RNA in human plasma with a branched DNA signal amplification assay. AIDS.](https://doi.org/10.1097/00002030-199311002-00004)\n8. [COBAS AmpliPrep/COBAS TaqMan HCV Test Package Insert (FDA)](https://www.accessdata.fda.gov/cdrh_docs/pdf6/P060030c.pdf)\n9. [Abbott RealTime HIV-1 Assay Package Insert](https://www.molecular.abbott/content/dam/add/molecular/products/pdf-/realtime-hiv-1-package-insert.pdf)\n10. [A collaborative study to establish the 1st WHO International Standard for human cytomegalovirus for NAT](https://www.sciencedirect.com/science/article/pii/S1045105616300070)\n11. [HIV-1 RNA Viral Load | Public Health Ontario](https://www.publichealthontario.ca/en/laboratory-services/test-information-index/hiv-viral-load)\n12. [HIVQN - Overview: HIV-1 RNA Detection and Quantification, Plasma (Mayo Clinic Laboratories)](https://www.mayocliniclabs.com/test-catalog/overview/113581)\n13. [Abbott RealTime HCV Assay Package Insert](https://www.molecular.abbott/content/dam/add/molecular/products/infectious-disease/realtime-hcv-viral-load/realtime-hcv-package-insert.pdf)\n14. [Bob van Gemen and colleagues (1993). Qualitative and quantitative detection of HIV-1 RNA by nucleic acid sequence-based amplification. AIDS.](https://doi.org/10.1097/00002030-199311002-00020)\n15. [D Kern and colleagues (1996). An enhanced-sensitivity branched-DNA assay for quantification of human immunodeficiency virus type 1 RNA in plasma. Journal of Clinical Microbiology.](https://doi.org/10.1128/jcm.34.12.3196-3202.1996)\n16. [John W. Mellors and colleagues (1996). Prognosis in HIV-1 Infection Predicted by the Quantity of Virus in Plasma. Science.](https://doi.org/10.1126/science.272.5265.1167)\n17. [Viral Load Tests, The AIDS InfoNet](https://www.aidsinfonet.org/fact_sheets/view/125)\n18. [cobas HIV-1 Quantitative nucleic acid test for use on the cobas 5800/6800/8800 Systems](https://elabdoc-prod.roche.com/eLD/api/downloads/bc02acf5-7b3c-ee11-1f91-005056a772fd?countryIsoCode=XG)\n19. [Implementation of pooled testing to increase access to routine viral load monitoring for people living with HIV on antiretroviral therapy (Scientific Reports, 2025)](https://www.nature.com/articles/s41598-025-92709-y)\n20. [Systematic Review of the Performance of HIV Viral Load Technologies on Plasma Samples](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0085869)\n21. [cobas HCV for cobas 6800/8800 Systems performance summary](https://diagnostics.roche.com/content/dam/diagnostics/Blueprint/en/pdf/rmd/RMD_cobas-HCV-for-cobas-68008800.pdf)\n22. [Laboratory diagnostic testing for cytomegalovirus infection in solid organ transplant patients](https://pmc.ncbi.nlm.nih.gov/articles/PMC9235525/)\n23. [Evaluation of Performance Characteristics of the Aptima CMV Quant Assay](https://pmc.ncbi.nlm.nih.gov/articles/PMC9945493/)\n24. [NYSDOH AI Virologic and Immunologic Monitoring in HIV Care (2025/2026 update)](https://www.hivguidelines.org/wp-content/uploads/2025/10/NYSDOH-AI-Virologic-and-Immunologic-Monitoring_3-31-2026_HG.pdf)\n25. [Technical and Regulatory Shortcomings of the TaqMan Version 1 HIV Viral Load Assay](https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0043882)\n26. [External quality assessment of HIV-1 DNA quantification assays used in the clinical setting in Italy](https://www.nature.com/articles/s41598-022-07196-2)\n\n---\n*Topic: Encyclopedia › Life and health › Human health and medicine › Clinical assessment and procedures › Diagnosis and clinical assessment › Laboratory and in-vitro diagnostics › Antimicrobial susceptibility testing*\n\n*Initially written Sep 29, 2026 · Reviewed: Sep 30, 2026 · Edited: Oct 15, 2026 · Last review: Sep 30, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/viral-load-testing", "markdown_url": "https://www.edgepedia.org/viral-load-testing.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Viral load testing\", Edgepedia (EdgeChat), https://www.edgepedia.org/viral-load-testing. Edgepedia Community License 1.0.", "credit_md": "\"[Viral load testing](https://www.edgepedia.org/viral-load-testing)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/viral-load-testing](https://www.edgepedia.org/viral-load-testing). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Viral load testing\", Edgepedia (EdgeChat), https://www.edgepedia.org/viral-load-testing. Edgepedia Community License 1.0.", "speakable": "Viral load testing measures the amount of virus in a patient's blood, reported as RNA or DNA copies per milliliter, to track infection and treatment response." }