QC

• Quality control


  A system of ensuring accuracy and precision in the laboratory by including quality control reagents in every series of measurements
• Quality control


  • It is a process of ensuring that analytical results are correct by testing known samples that resemble patient samples
  • It involves the process of monitoring the analytical process and detects analytical errors during testing, and prevents the reporting of inaccurate patient test results
• Parameters of quality control

  • Sensitivity
  • Specificity
  • Accuracy
  • Precision or reproducibility
  • Practicability
  • Reliability
  • Diagnostic sensitivity
  • Diagnostic specificity
• Sensitivity


  Ability of an analytical method to measure the smallest concentration of an analyte of interest
• Specificity


  Ability of an analytical method to measure ONLY the analyte of interest
• Accuracy


  Nearness or closeness of the assayed value to the true or target value
• Precision or reproducibility


  Ability of an analytical method to give repeated results on the same sample that agree with one another
• Practicability


  The degree by which a method is easily repeated
• Reliability


  The ability of an analytical method to maintain accuracy and precision over an extended period of time during which equipment, reagents and personnel may change
• Diagnostic sensitivity


  The ability of the analytical method to detect the proportion of individuals with the disease. Indicates the ability of the test to generate more true-positive results and few false-negative
• Diagnostic specificity


  The ability of the analytical method to detect the proportion of individuals without the disease. It reflects the ability of the method to detect true-negatives with very few false-positives. Confirmatory tests require high specificity to be certain of the diagnosis
• Kinds of quality control

  • Intralab quality control (internal QC)
  • Interlab quality control (external QC)
• Intralab quality control (internal QC)


  It involves the analyses of control samples together with the patient specimens. It detects changes in performance between the present operation and the "stable" operation. It is important for the daily monitoring of accuracy and precision of analytical methods. It detects both random and systematic errors in a daily basis. It allows identification of analytic errors within a one-week cycle
• Interlab quality control (external QC)


  It involves proficiency testing programs that periodically provide samples of unknown concentrations to participating clinical laboratories. It is important in maintaining long-term accuracy of the analytical methods. It is also used to determine state-of-the-art interlaboratory performance. The College of American Pathologists (CAP proficiency program is the gold standard for clinical laboratory external QC testing
• Rationale of the external QC/proficiency testing

  The ultimate goal of proficiency testing is to ensure our clinicians that patient results are accurate. Proficiency testing allows each laboratory to compare and evaluate test results or outcomes with those laboratories that use the same methods (reagents and equipment). Data obtained from the proficiency testing can be used to continuously improve test performance, and also serve as troubleshooting guide when investigating analytic error
• Objectives of quality control

  • To check the stability of the machine
  • To check the quality of reagents
  • To check technical (operator) errors
• Characteristics of an ideal QC material

  • Resembles human sample
  • Inexpensive and stable for long periods
  • No communicable diseases
  • No matrix effects/known matrix effects
  • With known analyte concentrations (assayed control)
  • Convenient packaging for easy dispensing and storage
• Electrophoresis


  The migration of charged particles in an electric field. It separates proteins on the basis of their electric charge densities. The acidic and basic amino acids determine the net charge on a protein, hence its electrophoretic mobility. During electrophoresis, proteins are negatively charged (anions) and they move towards the anode
• Components of electrophoresis


  • Electrical power
  • Support medium
  • Buffer
  • Sample
  • Detector
• Buffer


  Barbital (pH 8.6)
• Electrophoresis types


  • Gel electrophoresis
  • Paper electrophoresis
  • Capillary electrophoresis
• Chromatography


  It involves separation of soluble components in a solution by specific differences in physical-chemical characteristics of the different constituents
• Forms of chromatography


  • Planar
  • Column
• Planar chromatography


  • Paper chromatography
  • Thin layer chromatography (TLC)

  
• Paper chromatography


  It is used for fractionation of sugar and amino acid. Sorbent (stationary phase) - Whatman paper
• Thin layer chromatography (TLC)

  It is a semiquantitative drug screening test. Biological samples such as blood, urine and gastric fluid can be used for the test. Sorbent: thin plastic plates impregnated with a layer of silica gel or alumina
• Column chromatography


  • Gas chromatography (GC)
  • Liquid chromatography
• Gas chromatography (GC)


  It is used for separation of steroids, barbiturates, blood, alcohol and lipids. It is useful for compounds that are naturally volatile or can be easily converted into a volatile form. Samples (urine or blood) are introduced into the GC column using a hypodermic syringe or an automated sampler. Mobile phase: nitrogen, helium, hydrogen and argon (inert gases)
• Types of gas chromatography

  • Gas solid chromatography (GSC)
  • Gas liquid chromatography (GLC)
• Gas solid chromatography (GSC)


  Separation occurs based on differences in absorption at the solid phase surfaces
• Gas liquid chromatography (GLC)


  Separation occurs by differences in solute partitioning between the gaseous mobile phase and the liquid stationary phase
• Mass spectroscopy (MS)


  Based on the fragmentation and ionization of molecules using a suitable source of energy
• Gas chromatography - mass spectroscopy (GC-MS)

  Gold standard for drug testing. In this method, quantitative measurement of drug can be performed by selective ion monitoring
• Liquid chromatography


  It is based on the distribution of solutes between a liquid mobile phase and a stationary phase. HPLC is most widely used liquid chromatography

  
• High-performance liquid chromatography (HPLC)


  Uses pressure for fast separations, controlled temperature, in-line detectors
• Liquid chromatography-mass spectroscopy (LC-MS)


  It is used for detecting nonvolatile substances in body fluids
• Separation mechanisms used in liquid chromatography

  • Gel/gel permeation/gel filtration/size exclusion/molecular sieve chromatography
  • Ion exchange chromatography
  • Partition chromatography (liquid-liquid chromatography)
  • Affinity chromatography
  • Adsorption chromatography (liquid-solid chromatography)
• Gel filtration


  It is used for separating enzymes, antibodies, and proteins. Example: Dextran and Agarose
• Gel permeation


  It is for separation of triglyceride and fatty acid. Example: Sephadex
• Ion exchange chromatography


  The mechanism is the exchange of sample ions and mobile-phase ions with the charged group of the stationary phase. It is for separation of amino acids, proteins and nucleic acids. Separation of nucleic acids and proteins depends primarily on the sign and ionic charge density