Positive control

A positive control, in the context of laboratory testing and quality control, is a critical element used to validate the accuracy and reliability of an assay or experiment. It is a known sample that contains a predetermined amount of the targeted analyte or substance being tested for. Here are critical points about positive controls:

1. Quality Control: Positive controls are an essential part of quality control procedures in laboratory testing, including toxicology testing, enzyme-linked immunosorbent assay (ELISA) testing, and various analytical assays.
2. Purpose: The primary purpose of a positive control is to ensure that the experimental system, equipment, and procedures are functioning correctly and can reliably detect the analyte of interest. It provides a reference point with a known expected response.
3. Presence of AnalyteThe component of a system to be analyzed. More: Positive controls contain a known amount of the targeted analyte or substance under investigation. They are used to confirm that the assay or test can accurately detect and quantify the analyte when it is present.
4. Machine CalibrationThe act of checking or adjusting (by comparison with a standard) the accuracy of a measuring instrument. Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication. More: Positive controls are particularly valuable in assessing the performance of analytical instruments and detection systems. They help verify that the equipment can generate the expected response for the analyte.
5. Threshold and SensitivityIn the context of laboratory equipment or analytical techniques, the term "sensitive" describes the capability of a machine or method to detect even very small amounts or concentrations of a substance. Sensitivity is a quantitative characteristic that indicates the instrument's ability to accurately identify and measure low levels of a particular substance. Here are key points about sensitivity: • Detection of Small Amounts: Sensitivity measures how effectively a machine or technique can identify and quantify substances, even when present in very low concentrations or trace amounts.
   • Quantitative Characteristic: Sensitivity is typically expressed quantitatively, often in terms of the lowest amount or concentration of the substance that the instrument can reliably detect and measure.
   • Analytical Instruments: Sensitivity is especially important in analytical chemistry and laboratory instrumentation. Instruments like mass spectrometers, chromatographs, and spectrophotometers may be described as sensitive if they can detect minute quantities of compounds or molecules.
   • Applications: Sensitivity is crucial in various scientific fields, including environmental analysis, pharmaceuticals, toxicology, and clinical diagnostics. It enables the detection of contaminants, pollutants, drugs, or biomarkers at extremely low levels.
   • Threshold and Limits of Detection: Sensitivity is often associated with terms like "limit of detection" (LOD) and "limit of quantification" (LOQ). The LOD represents the lowest concentration of a substance that can be reliably detected, while the LOQ is the lowest concentration that can be accurately quantified.
   • Specificity vs. Sensitivity: Sensitivity should not be confused with specificity. While sensitivity relates to the instrument's ability to detect a wide range of substances, specificity refers to distinguishing between different substances and providing accurate identification.
   • Importance in Research and Testing: In scientific research and analytical testing, high sensitivity is desirable when dealing with samples containing low target analyte levels. It allows for precisely measuring and identifying compounds or substances of interest.
   • Instrument Calibration: Sensitive instruments often require meticulous calibration and maintenance to ensure their accuracy and reliability. Proper calibration is essential to maximize sensitivity.
   • Instrumentation Advances: Advances in technology have led to the development of increasingly sensitive analytical instruments, allowing scientists to explore and analyze samples with greater precision and detection capabilities.
   In summary, sensitivity refers to the ability of a machine or analytical technique to detect very small amounts or concentrations of a substance. It is a critical characteristic in scientific research, analytical chemistry, and laboratory testing, enabling the accurate measurement and identification of trace levels of target analytes. More: Positive controls also serve as threshold levels in some assays. For example, a positive control may represent the minimum concentration required for a positive result in ELISA testing for drugs or biomarkers. A test sample containing a concentration higher than the positive control is reported as positive for the analyte.
6. Assay ValidationValidation, often referred to as method validation, is a crucial process in the laboratory when introducing a new machine, technology, or analytical technique. It involves a series of systematic steps and assessments to ensure that the new method is reliable, accurate, and consistent in generating valid results. Here are key points about validation and method validation: • Introduction of New Methods: Validation is typically required when a laboratory introduces a new analytical method, instrument, or technology for testing, measurement, or analysis. This can include techniques like chromatography, spectrophotometry, or molecular assays.
   • Verification of Performance: The primary goal of validation is to verify that the new method or technology performs as expected and consistently provides accurate and reliable results.
   • Validation Procedure: The specific validation process can vary depending on the nature of the method or technology being validated. However, it typically involves a series of well-defined steps and criteria.
   • Known Samples: One common validation aspect is running known samples, often called validation or control samples. These samples are carefully selected, prepared, and analyzed using the new method.
   • Portfolio of Results: The results obtained from analyzing known samples are compiled into a portfolio or dataset. This dataset is examined and subjected to various statistical and analytical assessments.
   • Performance Evaluation: During the validation process, the method's performance is evaluated based on criteria such as accuracy, precision, specificity, sensitivity, linearity, and robustness. These criteria may vary depending on the type of analysis being conducted.
   • Acceptance Criteria: Acceptance criteria are established before validation begins. These criteria define the minimum acceptable performance levels the new method must meet for validity.
   • Documentation and Reporting: Rigorous documentation is a key aspect of validation. All aspects of the validation process, including procedures, results, and any deviations from acceptance criteria, are thoroughly documented and reported.
   • Time-Consuming Process: Method validation can be time-consuming, especially when working with large numbers of known samples. The process may involve the analysis of tens or even hundreds of samples.
   • Regulatory Requirements: In regulated industries such as pharmaceuticals, food safety, and clinical diagnostics, validation is often a mandatory requirement to ensure compliance with regulatory standards and guidelines.
   • Implementation: Once a new method successfully passes validation and meets the defined acceptance criteria, it can be implemented into the laboratory's routine procedures for analysis.
   • Continuous Monitoring: After implementation, ongoing monitoring and quality control measures are essential to ensure that the method continues to perform reliably over time.
   In summary, method validation is a rigorous and systematic process used to assess the performance and reliability of a new analytical method, instrument, or technology in the laboratory. It involves the analysis of known samples, documentation of results, and adherence to acceptance criteria to ensure that the method is fit for its intended purpose and consistently produces valid data. More: Positive controls are used to validate the accuracy and precision of the assay. Analysts can assess the reliability of their measurements by comparing the results of test samples to the response of the positive control.
7. Comparison and Quality Assurance: Positive controls are used for quality assurance and comparison in toxicology testing. They provide a known reference point to evaluate the assay’s performance and ensure it meets predetermined standards.
8. Confirmation and Reporting: In confirmatory toxicology assays, positive controls are used as part of the quality control process. However, they are not the sole factor in making a conclusive determination. Positive controls are used in conjunction with other data and criteria to reach a final conclusion about the presence or absence of a substance.
9. Preventing False Negatives: Positive controls help prevent false negative results, which are erroneous findings indicating the absence of an analyte when it is actually present.

In summary, positive control is essential to quality control in laboratory testing. It contains a known amount of the analyte of interest and is used to validate an assay or experiment’s accuracy, reliability, and sensitivity. Positive controls are valuable tools for ensuring the validity of results and maintaining the quality of testing processes.