Must To Know in Clinical Chemistry

• Quality Control

  • Practicability
  • Reliability
  • Maintain accuracy and precision
  • Intralab/Interlab QC
  • Daily monitoring of accuracy and precision
  • Interlab/External QC
  • Proficiency testing (Reference lab)
  • Long-term accuracy
• Difference of >2


  Not in agreement with other lab
• QC materials


  • Available for a min. of 1 yr
  • Bovine control materials (preferred, human biohazard)
  • Not for immunochem, dye-binding and bilirubin
• Matrix effect


  • Improper product manufacturing
  • Unpurified analyte
  • Altered protein
• Precision study

  First step in method evaluation
• Nonlab. personnel


  29% of errors (lab results)
• SD


  Dispersion of values from the mean
• CV


  • Index of precision
  • Relative magnitude of variability (%)
• Variance


  • SD2
  • Measure of variability
• Inferential statistics


  Compare means or SD of 2 groups of data
• 1. test


  Means of 2 groups of data
• 1. test


  SD of 2 groups of data
• Cumulative Sum Graph (CUSUM)


  Earliest indication of systematic errors (trend)
• Youden/Twin Plot


  Compare results obtained from different labs
• Shewhart Levey-Jennings Chart


  Graphic representation of the acceptable limits of variation
• Trend


  • Gradual loss of reliability
  • Cause: Deterioration of reagents (Systematic error)
• Shift


  • Values: one side or either side of the mean
  • Cause: Improper calibration (Systematic error)
• Outliers


  • Values: far from the main set of values
  • Highly deviating values
  • Random or systematic errors
• Kurtosis


  Degree of flatness or sharpness
• Precision


  Random error
• Accuracy


  Systematic error
• Causes of Random error

  • Mislabeling
  • Pipetting error
  • Improper mixing of sample and reagents
  • Voltage/Temperature fluctuation
  • Dirty optics
• Causes of Systematic error

  • Improper calibration
  • Deterioration of reagents
  • Contaminated solution
  • Sample instability/unstable reagent blanks
  • Diminishing lamp power
  • Incorrect sample and reagent volume
• Parameters for Random error

  SD and CV
• Multirule Shewhart procedure


  Control rules + Control chart
• Test method


  Westgard: at least 40 samples
• Reference method


  Westgard: preferably 100 samples
• Analytical Run


  Control and patient specimens assayed, evaluated, and report together
• Physiologic Limit


  Referred to as absurd value
• POCT


  Performed by nonlab personnel
• Quality Assurance


  • Program development
  • Assessment and monitoring
  • Quality improvement
• Quality Patient Care


  Test request forms, clear instruction for patient prep., specimen handling...
• Reference Range/ Interval


  At least 120 individuals should be tested in each age and sex category
• Wavelength


  • Distance between 2 successive peaks (nm)
  • Lower frequency = Longer wavelength (Ex. Red)
  • Higher frequency = Shorter wavelength (Ex. Violet)
• Spectrophotometric measurement


  Measures light intensity in a narrower wavelength
• Photometric measurement


  Measures light intensity without consideration of wavelength
• Multiple wavelength


  Uses filter only
• LASER


  • Light Amplification by Stimulated Emission of Radiation
  • Light source for spectrophotometry
• Light sources


  • Visible region: Tungsten light bulb, Mercury arc
  • UV: Deuterium lamp, Mercury arc, Xenon lamp, Hydrogen lamp
  • IR: Merst glower, Globar (Silicone carbide)
• Stray light


  • Wavelength outside the band
  • Most common cause of loss of linearity