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Laboratory test

Molecular Diagnostics

RT-PCR

RT-PCR is a Molecular Diagnostics laboratory test reference in the LabPedia Medical Laboratory Library. Reverse-transcription PCR converting RNA to cDNA before amplification; required for RNA viruses and gene-expression targets.

Also known asReverse-transcription PCR; RNA PCR (colloquial)

Overview

RT-PCR uses reverse transcriptase to synthesize complementary DNA from RNA, then amplifies the cDNA by PCR (endpoint or real-time).

Clinical Importance

Detect RNA pathogens (e.g., SARS-CoV-2, HCV, influenza)

Amplify RNA transcripts for fusion genes or expression assays

Specimen Requirements

  • Specimen: assay-validated specimen type (blood, swab, tissue, fluid, or other as ordered)
  • Collection: use the manufacturer-/SOP-specified collection device and preservative
  • Handling: avoid contamination with extraneous nucleic acid; change gloves between specimens
  • Transport: follow temperature and time limits for RNA (more labile) vs DNA targets
  • Stability: do not exceed validated storage limits; freeze–thaw cycles may reduce yield

Analytical Method

Extracted RNA is reverse-transcribed to cDNA (one-step or two-step protocols), then amplified. RNA-specific controls and RNase-aware handling are critical because RNA degrades readily.

Instruments Used

Automated analyzers

  • Applied Biosystems / Thermo Fisher real-time PCR systems (e.g., QuantStudio-class)
  • Roche Cobas molecular / LightCycler systems
  • Cepheid GeneXpert cartridge PCR systems
  • BioFire FilmArray syndromic PCR systems
  • Abbott m2000 / Alinity m molecular systems
  • Hologic Panther / Aptima molecular systems
  • Illumina next-generation sequencing platforms
  • Thermo Fisher Ion Torrent sequencing platforms
  • Digital PCR systems (e.g., Bio-Rad QX / QIAGEN QIAcuity-class)
  • Sanger capillary electrophoresis sequencers (Applied Biosystems)

Manual methods

  • Manual nucleic acid extraction, PCR setup, and gel/capillary analysis in selected workflows

Reference Values

Molecular cutoffs, units (IU/mL, copies/mL, Ct), reportable ranges, and variant classifications are assay- and laboratory-specific. Always interpret against the performing laboratory report, manufacturer IFU, and current CLSI / CAP / AMP / ACMG guidance as adopted locally. Limit of detection and inhibition controls are essential for negative results.

Assay-specific qualitative or quantitative results after RT and amplification. RNA integrity and LOD determine negative predictive performance.

Interpretation

Common Causes of Increased Results

  • Target RNA detected (or quantified above threshold) with valid RT/amplification controls

Common Causes of Decreased Results

  • Target not detected; does not exclude infection below LOD or after RNA degradation

Clinical Significance

  • RNA virus diagnostics
  • Oncology fusion transcript assays (e.g., BCR-ABL RNA)

Factors Affecting Results

Pre-analytical

  • Wrong specimen type or transport medium for the validated assay
  • Delayed transport degrading RNA targets
  • Contamination during collection (especially amplicon-rich environments)
  • Inadequate volume or low cellularity/tumor content
  • RNA degradation from delayed processing or improper storage

Analytical

  • PCR inhibition (heparin, humic acids, excess hemoglobin; assay-dependent)
  • Extraction failure or pipetting/contamination in amplification areas
  • Probe/primer mismatch with sequence variants causing false negatives
  • Calibration/QC failure; expired reagents

Post-analytical

  • Reporting Ct or raw copies without assay-specific interpretive rules
  • Misapplying another laboratory’s LOD or units
  • Variant classification without current ACMG/AMP framework when required

Advantages and Limitations

Advantages

  • Enables RNA target detection

Limitations

  • RNA lability
  • Extra enzymatic step vs DNA PCR

Clinical Pearls

RT-PCR failures are often RNA handling failures; cold chain and extraction beat primer design debates.

Related Laboratory Tests

References

Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.

Textbooks

  • McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021. (Molecular diagnostics chapters, verify current edition.)
  • Buckingham L. Molecular Diagnostics: Fundamentals, Methods, and Clinical Applications. 3rd ed. F.A. Davis; 2019. (Verify current edition and institutional adoption.)

CLSI and Professional Guidelines

  • Clinical and Laboratory Standards Institute (CLSI). Consult current CLSI molecular method documents available through your laboratory, document numbers and editions change; do not treat any single CLSI title as universal.
  • Institutional molecular laboratory standard operating procedures (SOPs), assay manufacturer instructions for use (IFU), and locally adopted accreditation requirements. Always verify current local practice.
  • Clinical and Laboratory Standards Institute (CLSI). Molecular method evaluation and related documents (verify current CLSI editions applicable to the assay).
  • College of American Pathologists. Molecular pathology accreditation and proficiency testing expectations (verify current CAP checklist requirements).
  • Association for Molecular Pathology (AMP). Practice guidelines and position statements for molecular diagnostics (verify current AMP documents for the assay).
  • American College of Medical Genetics and Genomics (ACMG). Standards and guidelines for interpretation of sequence variants and related genetic testing practice (verify current ACMG documents).

WHO Publications

  • World Health Organization. Laboratory and diagnostic guidance relevant to molecular testing (verify current WHO publication for the assay/pathogen).

Frequently Asked Questions

Common questions about using this RT-PCR laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.

What is the RT-PCR laboratory test reference used for?

This Medical Laboratory Library page summarizes the clinical importance of RT-PCR. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.

Where can I find RT-PCR specimen requirements?

See the Specimen Requirements section on this page for specimen information related to RT-PCR. Confirm collection details against your laboratory protocol.

Where are RT-PCR reference values listed?

See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.

How do I interpret RT-PCR results?

Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.

What analytical method is used for RT-PCR?

See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.

Are related laboratory tests linked from RT-PCR?

Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.

How can I continue learning after reading RT-PCR?

Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Molecular Diagnostics topic.

What are the clinical pearls for RT-PCR?

See the Clinical Pearls section for concise laboratory practice notes associated with RT-PCR. Apply pearls alongside institutional protocols.

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