Overview
Sanger sequencing determines the nucleotide order of a targeted DNA fragment using fluorescent dideoxy terminators and capillary electrophoresis.
Clinical Importance
Confirm variants detected by other methods
Sequence defined exons/hotspots when NGS is unnecessary
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
A purified PCR amplicon undergoes cycle sequencing with ddNTPs; fragments are separated by capillary electrophoresis and base-called. Bidirectional sequencing is preferred for clinical confirmation. Sensitivity for mosaic/low-level variants is limited vs NGS/dPCR.
Instruments Used
Automated analyzers
- Applied Biosystems capillary electrophoresis sequencers
- Thermal cyclers for cycle sequencing
Manual methods
- Manual PCR cleanup and sequencing reaction setup
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.
Sequence compared to a reference; variants reported with HGVS nomenclature when applicable. Heterozygous peaks appear as mixed base calls; allele fraction below ~15–20% may be missed.
Interpretation
Common Causes of Increased Results
- Variant identified; classify per ACMG/AMP (germline) or oncology frameworks as appropriate
Common Causes of Decreased Results
- Wild-type sequence in covered region; does not exclude variants outside primers or large deletions/duplications
Clinical Significance
- Single-gene confirmation
- Fill-in sequencing for NGS gaps
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
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
- High accuracy for targeted regions
- Widely understood confirmation method
Limitations
- Limited throughput and region size
- Poor for large rearrangements and low-level mosaicism
Clinical Pearls
Sanger reads what your primers amplify; a clean chromatogram outside the mutation still means nothing for the exon you never covered.
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 Sanger Sequencing laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Sanger Sequencing laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Sanger Sequencing. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Sanger Sequencing specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Sanger Sequencing. Confirm collection details against your laboratory protocol.
Where are Sanger Sequencing 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 Sanger Sequencing 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 Sanger Sequencing?
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 Sanger Sequencing?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Sanger Sequencing?
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 Sanger Sequencing?
See the Clinical Pearls section for concise laboratory practice notes associated with Sanger Sequencing. Apply pearls alongside institutional protocols.
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