Technical Principles of Chemiluminescence Immunoassay for Detecting Abnormal Prothrombin and Key Performance Elements of the Kit

Detection principle: Double-antibody sandwich and chemiluminescent signal system

Abnormal prothrombin assay kits (chemiluminescence immunoassay) generally employ a double-antibody sandwich format. Anti-human abnormal prothrombin monoclonal antibodies coated on magnetic microparticles capture PIVKA-II in the sample. After washing, another antibody recognizing a different epitope (labeled with acridinium ester, alkaline phosphatase, horseradish peroxidase, or other luminescent/enzymatic components) is added. Following a second incubation and wash, trigger solution is added to initiate the chemiluminescent reaction. The light signal is collected by a photomultiplier tube, and its relative light unit (RLU) value is positively correlated with the PIVKA-II concentration in the sample within a certain range. Common luminescence systems include direct chemiluminescence (e.g., acridinium ester-hydrogen peroxide) and enzymatic chemiluminescence (e.g., horseradish peroxidase-luminol system). The former requires no catalyst and reacts rapidly; the latter provides better signal stability. Different manufacturers may use different label and substrate combinations, but the basic principle is the same.

Key determinants of kit performance

The performance indicators for evaluating abnormal prothrombin assay kits (chemiluminescence immunoassay) mainly include sensitivity, precision, specificity, linear range, and anti-interference capability. The following factors significantly affect performance:

Antibody selection: The double-antibody sandwich method requires two antibodies that recognize different antigenic epitopes with minimal steric hindrance. Antibodies specific for the abnormal carboxylation domain in the PIVKA-II molecule are central to ensuring detection specificity. If antibodies cross-react with normal prothrombin or other vitamin K-dependent coagulation proteins, false positives will increase.

Matrix effects: Bilirubin, hemoglobin, lipids, and anticoagulants in serum may interfere with antigen-antibody binding or the luminescent signal. Kits typically reduce matrix effects by adding blocking agents and optimizing diluent formulations. When establishing local reference intervals, laboratories should validate using pooled serum from the local population.

Calibrator value assignment and traceability: Kit calibrators must be traceable to international standards or the manufacturer's internal reference materials (e.g., WHO PIVKA-II international standard). The accuracy of value assignment directly affects the reliability of test results. Users should regularly monitor calibration curve stability using high and low concentration quality control materials.

Methodological comparison and limitations

Compared with traditional enzyme-linked immunosorbent assay (ELISA), abnormal prothrombin assay kits (chemiluminescence immunoassay) offer significant advantages in automation, detection speed, and sensitivity. Chemiluminescence methods typically reduce detection time to 30–60 minutes, whereas ELISA requires 2–4 hours. However, chemiluminescence methods have higher requirements for reagent and instrument compatibility, and systematic differences in test results may exist between different platforms. Therefore, continuous test data from the same platform should be used whenever possible for clinical judgment. In addition, serum should be separated as soon as possible after sample collection to avoid repeated freeze-thaw cycles that cause PIVKA-II degradation. Generally, samples should not be kept at room temperature for more than 2 hours or at 2–8°C for more than 24 hours. For long-term storage, samples should be kept at -20°C or below.

Practical points for quality control

To ensure accurate and reliable abnormal prothrombin test results, laboratories should implement the following measures:

Daily quality control runs: Include at least two levels—normal and pathological values. Quality control results should be in control (e.g., Westgard rules).

Regular calibration: Calibrate at the frequency recommended in the reagent instructions (typically per batch or every two weeks). Recalibration is mandatory when changing reagent lot numbers.

Participation in external quality assessment: Evaluate result consistency between the laboratory and peers through EQA programs organized by the National Center for Clinical Laboratories of the National Health Commission or provincial institutions.

Reagent management: Store strictly according to storage conditions, avoid direct sunlight, and observe the post-opening expiration period (generally use within 28 days after opening).

The above quality control steps are the foundation for ensuring the clinical application value of the kit. In promotional materials or literature citations, claims such as "error-free" or "absolutely accurate" should be avoided; instead, neutral expressions such as "meets expected performance" or "satisfies clinical needs" should be used.