analysis

• Sections of the Medical Laboratory

  • Clinical Chemistry
  • Immunology and Serology
  • Blood Banking
  • Histopathology
  • Clinical Microscopy
  • Molecular Diagnostics
• Analytic determination in clinical laboratory

  Based on measurements of radiant energy that is absorbed or transmitted
• Photometers or spectrophotometers


  Devices used to measure absorbed or transmitted light energy
• Basic components of spectrophotometers

  • Radiant energy source
  • Wavelength selector
  • Cuvette holder
  • Photodetector
  • Signal processor
  • Readout devices
• Beer-Lambert Law


  Absorbance and percent transmittance are inversely related
• Absorbance is directly proportional to the path length, through the medium and the concentration of the absorbing species
• Reflectometer


  Used to measure analytes by measuring the quantity of light reflected by a liquid sample that has been dispensed onto a grainy or fibrous solid support
• Nephelometer


  Used to detect scattered light at various angles, used in detecting antigen-antibody complexes
• Refractometry


  Based on light refraction, used to measure protein concentration, specific gravity of urine, and concentration of solutes in column effluent of HPLC
• Flow Cytometer


  Measures light patterns produced as particles pass single file through a laser light beam, used to count and sort cells
• Electrochemical techniques


  • Potentiometry
  • Amperometry
  • Coulometry
  • Conductivity
  • Anodic stripping voltammetry
• Potentiometry


  Measurement of potential (voltage) between two electrodes in a solution, utilizes the indicator electrode and reference electrode, measures potential using the Nernst equation
• Coulometry


  Measures the quantity of electricity (in coulombs) needed to convert an analyte to a different oxidation state, used to measure chloride ion in serum, plasma, CSF, and sweat samples
• Voltammetry


  Method where a potential is applied to an electrochemical cell and the resulting current is measured, most important advantages are sensitivity and capability for multielement measurements
• Anodic stripping voltammetry


  Electrochemical technique used to measure heavy metals such as lead
• Electrophoresis


  Separation of charged compounds based on their electrical charge, used to separate the proteins in serum, urine, and other body fluids
• When voltage is applied to a salt solution (usually NACl), an electrical current is produced by the flow of ions: cations toward the cathode and anions toward the anode
• Conductivity of a solution increases with its total ionic concentration
• Once completed, the support medium is treated with a dye to identify the separated fractions
• To obtain a quantitative profile of the separated fractions, densitometry is performed on the stained support medium
• Chromatography


  Separation techniques based on the different interaction of specimen compounds with a mobile phase and stationary phase, as the compound travels through a support medium
• Gas Chromatography


  Combined with Mass Spectrometry, is the reference method for drug testing
• Liquid Chromatography


  Uses lower temperatures for separation, thereby achieving better separation of thermolabile compounds
• HPLC


  Analysis time are usually much shorter and reproducibility is greatly improved, often used as the worldwide standard principle of measuring glycosylated hemoglobin (HbA1c), uses small, rigid supports and special mechanical pumps, producing high pressure to pass the mobile phase through the column
• Mass Spectrometry


  Based on fragmentation and ionization of molecules, the relative abundance of each of the ions yields a characteristic mass spectrum of the parent molecule, basic components include an ion source, a mass analyzer, and an ion detector, widely used in the clinical laboratory for determination of the concentrations of therapeutic drugs or drugs of abuse in patients' sera or urine, amino acid sequencing of proteins, and proteomic analysis of proteins in sera and other body fluids to diagnose specific disease, primary method for identification of bacteria and other organisms in the microbiology laboratory, Tandem Mass Spectrometry (MS-MS) is now the reference method for analyzing analytes for the detection of Inborn Error of Metabolism (IEM)
• Impedance


  Electrical impedance measurement is based on the change in electrical resistance across an aperture when a particle in conductive liquid passes through this aperture, primarily used in hematology laboratories to enumerate leukocytes, erythrocytes, and platelets
• Scintillation Counter


  Used to quantitate the level of radioactive emissions from radiolabeled compounds
• NMRS (Nuclear Magnetic Resonance Spectroscopy)


  Nondestructive; used as a diagnostic imaging technique, it has been adapted for only a limited number of clinical laboratory analyses, the most popular being lipoprotein particle measurements
• Types of Quality Control


  • Internal QC
  • External QC or Proficiency Testing
• Internal QC


  Type of QC in which machines or equipments used in the actual measurement process are checked by running controls prepared daily
• External QC or Proficiency Testing

  Proficiency testing provides external evaluation that a laboratory is using a method correctly and in conformance with the manufacturer's specifications, Philippine laboratories assess their reliability in testing through the conduct of NEQAS
• In an unacceptable QC result, corrective action is taken to fix the method problem, all the patient results since the time of the previous acceptable QC result are repeated to determine whether a result correction is needed