Overview
D-dimer assays detect cross-linked fibrin degradation fragments generated when plasmin lyses a fibrin clot.
Clinical Importance
As part of validated VTE exclusion algorithms in outpatients with low/intermediate clinical probability
As a supportive marker of fibrin turnover in DIC and related contexts
Specimen Requirements
- Specimen: platelet-poor plasma prepared from whole blood
- Tube: light-blue top; 3.2% sodium citrate (0.109 mol/L)
- Anticoagulant ratio: 9:1 blood-to-citrate (CLSI H21); fill to the tube fill line
- Handling: invert gently; transport promptly; avoid traumatic draws and line heparin contamination
- Processing: centrifuge to platelet-poor plasma per institutional protocol before testing
- Stability: assay-specific (CLSI H21). aPTT is generally less stable than PT; do not exceed validated time/temperature limits for the ordered tests.
Analytical Method
Monoclonal antibodies recognize D-dimer epitopes in latex agglutination, immunoturbidimetric, or ELISA-format assays. Results are reported in FEU or DDU; units are not interchangeable without conversion.
Instruments Used
Automated analyzers
- Sysmex CS / CN coagulation analyzers
- Werfen / Instrumentation Laboratory ACL TOP coagulation analyzers
- Siemens Healthineers BCS coagulation analyzers
- Stago STA Compact / STA R Max coagulation analyzers
- Dedicated immunoassay modules for D-dimer on chemistry/coagulation lines
Manual methods
- Semi-quantitative latex agglutination card methods (limited settings)
Reference Values
Typical adult SI examples below follow widely published international hematology practice (e.g., Dacie and Lewis; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and altitude intervals differ.
Cutoffs are method- and unit-specific (fibrinogen-equivalent units [FEU] vs D-dimer units [DDU] are not interchangeable without conversion).
Many FEU VTE-exclusion assays use a cutoff of 500 µg/L FEU (0.50 mg/L FEU; numerically equivalent to 500 ng/mL FEU on some reports) in selected adult outpatients. Age-adjusted cutoffs apply in some validated pathways; confirm the assay insert and local protocol.
Interpretation
Common Causes of Increased Results
- Elevated D-dimer indicates fibrin turnover but is nonspecific (VTE, DIC, pregnancy, inflammation, age, surgery)
Common Causes of Decreased Results
- D-dimer below a validated exclusion cutoff supports ruling out VTE only within an approved clinical algorithm
Clinical Significance
- VTE exclusion with pretest probability tools
- Supportive DIC laboratory panels
Factors Affecting Results
Pre-analytical
- Underfilled citrate tube (excess anticoagulant prolongs clotting times)
- Overfilled tube or clot in specimen
- Hematocrit >55% may require adjusted citrate volume (CLSI H21 guidance)
- Delayed processing or improper storage beyond assay stability
- Heparin contamination from line draws
Analytical
- Reagent lot / instrument calibration differences
- Lipemia, hemolysis, or icterus interfering with photo-optical endpoints
Post-analytical
- Using a VTE cutoff without clinical probability assessment
- Confusing FEU and DDU units
Advantages and Limitations
Advantages
- High sensitivity in validated VTE exclusion pathways
- Rapid automated immunoassays
Limitations
- Low specificity; many hospitalized patients are positive
- Not a stand-alone diagnostic test for thrombosis
Clinical Pearls
A positive D-dimer does not diagnose PE/DVT; a negative result only helps when the clinical pathway says it can.
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.
- Rodak BF, Carr JH. Rodak's Hematology: Clinical Principles and Applications. 6th ed. Elsevier; 2020.
- Hoffbrand AV, Moss PAH, Pettit JE. Essential Haematology. 8th ed. Wiley-Blackwell; 2019.
- McKenzie SB, Williams JL. Clinical Laboratory Hematology. 4th ed. Pearson; 2022.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
- Kaushansky K, et al. Williams Hematology. 10th ed. McGraw-Hill; 2021.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays; Approved Guideline. CLSI document H21-A5. CLSI; 2017.
- Clinical and Laboratory Standards Institute. One-Stage Prothrombin Time (PT) Test and Partial Thromboplastin Time (PTT) Test; Approved Guideline. CLSI document H47-A2. CLSI; 2008.
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Management of Critical- and Significant-Risk Results. CLSI guideline GP47-Ed1. CLSI; 2015.
Frequently Asked Questions
Common questions about using this D-Dimer laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the D-Dimer laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of D-Dimer. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find D-Dimer specimen requirements?
See the Specimen Requirements section on this page for specimen information related to D-Dimer. Confirm collection details against your laboratory protocol.
Where are D-Dimer 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 D-Dimer 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 D-Dimer?
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 D-Dimer?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading D-Dimer?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Hematology topic.
What are the clinical pearls for D-Dimer?
See the Clinical Pearls section for concise laboratory practice notes associated with D-Dimer. Apply pearls alongside institutional protocols.
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