QUALITY CONTROL
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Ability of analytical method to measure the smallest concentration of analyte
Sensitivity
Ability of analytical method to measure only the analyte of interest
Specidicity
Nearness or closeness of the assayed value to the true or target value
Accuracy
Ability of analytical method to give repeated results on the same sample
Precision or Reproducivility
Degree by which a method is easily repeated
Practicability
Ability to maintain accuracy and precision over an extended period of time
Reliability
Ability of analytical method to detect proportion of individuals without the disease
Diagnostic Specificity
Ability of analytical method to detect proportion of individuals with the disease
Diagnostic Sensitivity
Sensitivity (%)
100 x number of true positive / total number of diseased
Specificity (%)
100 x number of true negative / total number of without disease
Error due to chance, varies from sample to sample
Random Error
Due to instrument, operator and environmental conditions such as: > pipetting error > mislabeling of samples > temperature fluctuation > improper mixing of sample and reagent
Random Error
Error that influences observations consistently in one direction
Systematic Error
Due to: - Calibration problems - Deterioration of reagents and control materials - Improperly made standard solutions - Contaminated solutions - Unstable and Inadequate reagent blanks - Leaky ion selective electrode - Failing instrumentation and - Poorly written procedures
Systematic Error
Difference between the target value and the assayed value
Constant Error
Results in greater deviation from the target value due to higher sample concentration
Proportional/ Slope/ Percent Error
Highest frequency of Clerical errors occurs with
Use of handwritten labels and Request forms
Objectives of Quality Control
• Check stability of the machine • Check quality of reagents • Check technical errors
Levels of control solutions in General Chemistry
TWO levels
Levels of control solutions in Immunoassays
THREE levels
Characteristics of an Ideal QC material
• Resembles human sample • Inexpensive and stable for long periods • No communicable diseases • No matrix effects • With known analyte concentrations • Convenient packaging for easy dispensing and storage
Incorrect patient identification Improper patient preparation Incorrect specimen collection Mislabeled specimen Incorrect order of draw Incorrect used of tubes for blood collection Incorrect anticoagulant to blood ratio Improper mixing of blood and anticoagulant Incorrect specimen preservation Mishandled specimen Incorrectly interpreted/ ordered laboratory test Incomplete centrifugation Incorrect data login
Pre-Analytical Errors
Incorrect sample and reagent volume Incorrect incubation of solution Equipment/ Instrument malfunction Improper calibration of equipment/ Calibration errors
Analytical Errors
Unavailable or delayed laboratory results Long turnaround time Incomplete laboratory results Wrong transcription of the patient’s data and laboratory results Missing laboratory results Laboratory results submitted to the wrong physician/ doctors who did not request for the lab test
Post-analytical Errors