In vitro diagnostics (IVD) refers to techniques that obtain clinical diagnostic information by testing and analyzing human samples (such as blood, body fluids, and tissues) outside the human body.IVD plays a vital role in disease prevention, diagnosis, treatment monitoring, and prognosis assessment. The standardization and accuracy of its procedures directly impact the reliability of test results, which in turn influences clinical decision-making. This article will detail the main IVD procedures and key considerations.
Sample Collection and Processing
The first step in IVD is sample collection, the quality of which directly impacts the accuracy of subsequent testing. Sample types vary for different tests, with common examples including blood, urine, saliva, and cerebrospinal fluid.
1.Sample Collection Standards
•Blood samples: Blood samples are typically collected by venipuncture, using sterile blood collection tubes and an appropriate anticoagulant (such as EDTA, heparin, or sodium citrate) based on the test being performed. Care must be taken to avoid hemolysis, coagulation, and contamination during blood collection. •
Urine Sample: First-morning urine or random urine is generally used. The urethra should be cleaned before collection to avoid contamination with secretions. Certain tests (such as 24-hour urine protein quantification) require a full-day urine collection and the total volume recorded.
•Other samples: Tissue samples, such as those obtained through biopsy and cerebrospinal fluid, must be collected through lumbar puncture. Strict aseptic procedures must be followed.
2.Sample Transportation and Storage
•Samples should be sent for testing as soon as possible after collection. If testing is not possible immediately, they should be refrigerated (2-8°C) or frozen (-20°C or colder) according to the test requirements.
•Certain tests (such as nucleic acid tests) require high sample stability and require the use of specialized storage solutions or cold chain transportation.
Reagent and Instrument Preparation
In vitro diagnostics rely on high-quality reagents and precision instruments. Before use, ensure that the reagents and equipment meet the test requirements.
1.Reagent Preparation
•Reagents should be stored according to the instructions and avoid repeated freezing and thawing or use beyond the expiration date. •
Certain reagents (such as antibodies for enzyme-linked immunosorbent assays (ELISAs)) require prewarming or dilution to ensure reaction sensitivity.
2.Instrument Calibration and Quality Control
•Testing instruments (such as biochemical analyzers, PCR instruments, and immunoassay analyzers) require regular calibration to ensure measurement accuracy.
•Quality control samples should be run before each test to verify the stability of the test system and avoid biased results due to instrument errors.
Test Procedure
The specific steps for in vitro diagnostics vary depending on the test technology, but generally include sample preparation, reaction system preparation, test execution, and data reading.
1.Sample Preparation
•Certain tests (such as nucleic acid tests) require nucleic acid extraction from the sample, typically using magnetic bead or column extraction methods.
•Biochemical tests may require centrifugation of serum or plasma to eliminate interference from cellular components.
2.Reaction System Preparation
•Mix the sample and reagents in the appropriate proportions according to the test requirements, ensuring that reaction conditions (such as pH and temperature) meet the standards.
•Automated instruments typically dispense reagents and samples automatically, but manual operation requires strict control of sample volume to avoid errors.
3.Test Execution
•Immunological assays (e.g., ELISA, chemiluminescence): Detect target substances through antigen-antibody binding reactions, typically requiring incubation, washing, and signal detection steps.
•Molecular biology assays (e.g., PCR): Detection is performed by amplifying specific DNA/RNA fragments, requiring strict temperature cycling (denaturation, annealing, and extension).
•Biochemical assays (e.g., blood glucose, liver function markers): Based on enzymatic reactions or colorimetric methods, the instrument measures absorbance or electrochemical signals.
4.Data Reading and Analysis
•After the test is completed, the instrument typically generates results automatically, but interpretation must be based on clinical significance.
•Some assays (e.g., immunofluorescence) may require manual microscopic observation, with expert technicians interpreting the results.
Quality Control and Result Reporting
1.In-House Quality Control (IQC)
•Laboratories must run high and low-value quality control samples daily to ensure that test results are within acceptable limits. If quality control is out of control, the cause must be investigated and retesting must be conducted.
2.External Quality Assessment (EQA)
•Participate in quality assessment programs organized by external organizations and compare results with other laboratories to ensure the accuracy and comparability of testing methods.
3.Result Reporting
•Test results should be issued in a standardized format, including the test item, value, reference range, and test method.
•Abnormal results must be labeled and analyzed in light of the clinical context. If necessary, re-examination or further testing may be recommended.
Summary
The operation of in vitro diagnostics involves multiple steps, including sample collection, reagent preparation, instrument testing, and quality control. Each step must strictly adhere to standardized procedures to ensure the accuracy and reliability of test results. While technological advancements have led to the increasing prevalence of automated and high-throughput testing methods, operators still require professional knowledge and a rigorous approach to ensure the effectiveness of in vitro diagnostics in clinical applications.