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ELISA clinical quality evaluation and quality management
ELISA reagents are evaluated from two perspectives: the quality of the reagent itself and its performance in clinical settings. For instance, hepatitis B ELISA diagnostic reagents must first pass verification by Chinese pharmaceutical biological product authorities to obtain a production license. Beyond packaging, labeling, and instructions, their performance—such as specificity, sensitivity, precision, and linearity—must be thoroughly tested. This involves analyzing a series of reference samples to ensure that the results meet required standards.
In terms of clinical application, the quality of ELISA reagents is assessed based on their ability to distinguish between healthy and diseased states. Although no test is 100% accurate, the reliability of a test is often measured by its sensitivity (the percentage of true positive results among patients with the disease) and specificity (the percentage of true negative results among non-diseased individuals). To evaluate this, researchers collect patient serum samples and use the most reliable reagent to determine whether each sample is positive or negative. These samples form what is known as a "serum disk," which serves as a benchmark for assessing the performance of the evaluated reagents.
For an ELISA reagent to be considered effective, it should have a coincidence rate above 90%, indicating good agreement between the test results and the reference standard. The serum disk used for evaluation should meet several criteria: it should consist of human original serum, have stable components, contain minimal or no preservatives, include an equal number of positive and negative samples, and have both strong and weak positive samples. It should also include samples with critical values to test sensitivity and samples with interfering substances to assess specificity.
An example of this process involved the evaluation of anti-HBc-IgM reagents. The Clinical Examination Department collected nearly 100 clinical samples, screened them using the Abbott anti-HBc-IgM reagent, and selected 70 samples—29 positive and 41 negative—for further testing. Among these, 22 were confirmed to be positive, including cases of acute, chronic active, and severe hepatitis, while 40 were negative, covering various stages of chronic hepatitis. These samples were then used to evaluate commercial reagents, helping to identify those capable of distinguishing between different types of hepatitis patients.
Quality control is essential in ELISA procedures, as the method is highly sensitive, specific, and reproducible. It is widely used in microbiology, parasitology, oncology, and cytokine detection due to its ease of use, stability, and objective interpretation. However, many factors can affect the accuracy of results, making strict quality management crucial.
Pre-analytical quality control involves proper training of personnel, ensuring they understand the principles of ELISA, the clinical significance of tests, and how to handle reagents and instruments correctly. Specialized training is required for certain tests, such as anti-HIV screening, to ensure accuracy and compliance.
The ELISA technique, developed in 1971 by Engvall et al., involves immobilizing immunologically active substances on a solid surface, followed by enzyme-labeled detection. While it offers high sensitivity and specificity, it has limitations, such as a narrow linear range and potential issues like the "hook effect."
ELISA methods vary depending on the purpose, including sandwich assays for antigens, indirect methods for antibodies, and competitive assays for small molecules. Future developments may focus on improving surface preparation and signal amplification techniques, such as enzymatic fluorescence or chemiluminescence.
In clinical practice, ELISA plays a key role in diagnosing various types of hepatitis. Understanding the markers and their significance helps in interpreting results accurately. For example, HBsAg, HBeAg, and HBcAb-IgM are indicators of viral replication and infection status.
When selecting ELISA kits, it is important to choose products verified by the Ministry of Health, ensuring they are sensitive, specific, and stable. Kits should also be easy to use, safe, and cost-effective. Sensitivity refers not only to the lowest detectable level but also to the ability to minimize false negatives across large sample sets.