Laboratory testing as the basis of modern medicine: from methodology to clinical significance

Fundamental aspects of laboratory testing: accuracy, validity, and clinical interpretation

Laboratory testing is a cornerstone of modern diagnostics, as it provides doctors with objective quantitative data about a patient's health. It is estimated that over 70% Clinical Solutions are based on the results of laboratory tests. The quality of further treatment and prognosis of diseases depends on the correct choice of method, the accuracy of the test, and the correct interpretation of the result. This material is devoted to an in-depth analysis of the key parameters that ensure the reliability of laboratory data.

Testing Quality: Preanalytical, Analytical and Postanalytical Stages

The reliability of any laboratory result depends on strict control at three main stages:

1. Pre-analytical stage: Basis of reliability

This is the least controlled stage by the laboratory, but it is critically important. It includes patient preparation, collection of biological material (blood, urine, cerebrospinal fluid, etc.), labeling, storage, and transportation to the laboratory. For example, improper preparation (eating before the glucose tolerance test) or improper storage of the sample (excessive heating) can lead to falsely overestimated or underestimated results.

2. Analytical stage: Method accuracy

At this stage, the sample is directly analyzed. Standardized methods such as enzyme-linked immunosorbent assay (ELISA) are used.ELISA), polymerase chain reaction (PCR), mass spectrometry, and flow cytometry. Internal and external quality control are mandatory to ensure accuracy (closeness of the measured value to the true value) and precision (repeatability of results) of the equipment.

3. Post-analytical stage: Interpretation and validation

This stage includes checking the results, validating them by the laboratory technician, and transmitting them to the clinician. Even a technically correct result can be clinically erroneous if it is not correlated with the patient's age, gender, medical history, and medication intake.

Validity and standardization of methods in clinical biochemistry

To ensure global comparability and reliability, laboratory tests are guided by international standards.

• Reference ranges: These are the ranges of values observed in 95% healthy population. They depend on the method, equipment and population. Correct interpretation requires the use of reference values established by the specific laboratory where the analysis was performed.
• Clinical validity: This is the degree to which a test accurately measures what it is supposed to measure, given the clinical setting. For example, how accurately a C-reactive protein (CRP) test correlates with the actual inflammatory process.
• Sensitivity and Specificity: Two key parameters that determine the effectiveness of the test.

According to the guidelines FDA (US Food and Drug Administration), medical devices and diagnostic tests are subject to rigorous sensitivity and specificity evaluation before being released to the market to ensure minimal risk of false-positive or false-negative results.

Analysis and interpretation of results in clinical practice

Simply comparing the result with the reference range is not sufficient. Clinical interpretation requires consideration of a number of factors:

• Biological variation: Each indicator has individual biological variation. For example, the level cortisol depends on the time of day (circadian rhythm), and the level creatinine — from muscle mass and diet.
• Interference: The presence of certain substances in the sample (e.g., medications, high bilirubin levels, or lipemia) can interfere with the chemical reactions in the test, leading to distorted results.
• Comparison with dynamics: The most informative is not a single result, but dynamics of change indicator over time. If a previously high indicator decreases to the upper limit of normal during treatment, this may indicate a positive response from the body.

Mayo Clinic emphasizes that each laboratory result should be considered as part of a larger clinical picture, not as a diagnosis in itself. A comprehensive approach that includes physical examination, medical history, and laboratory data is key to an accurate diagnosis.

The future of laboratory diagnostics

Technological developments, especially in the field of molecular diagnostics (e.g. next-generation sequencing), are opening up new perspectives. This allows us to move from diagnosing an existing disease to personalized and predictive medicine. Molecular testing already helps identify genetic predisposition to certain diseases and select targeted therapy (pharmacogenetics), ensuring maximum treatment effectiveness.

Laboratory testing is a high-tech process that requires constant improvement of methodology and strict adherence to international standards, which is guaranteed through quality control systems recommended by organizations such as WHO and FDA. Ultimately, a reliable laboratory result is a fundamental element in maintaining and restoring a patient's health.

Sources

1. World Health Organization (WHO). Guidance on regulations for the in vitro diagnosis (IVD) industry. 2021.
2. US Food and Drug Administration (FDA). In Vitro Diagnostics. Official guidelines and device classification.
3. Mayo Clinic Laboratories. Test Ordering and Interpretation Policies. Guidelines on preanalytical variables and result validation.