5.7 - Fundamental Concepts of TQM (Analytical Errors in the Clinical laboratory)

Question 1

Analytical errors in the laboratory can be classified into two groups:

Answer 1

1. Random Errors
2. Systematic Errors

Question 2

These are imprecision of the test system which causes a scatter or spread of control values around the mean due to errors which vary from one sample to another. The exact magnitude of which cannot be predicted. It is detected as positive or negative bias for a given analytical method. It is estimated by repetitive testing or precision studies.

Answer 2

Random Errors

Question 3

Common causes of Random Errors include:

Answer 3

i. handling techniques (non-vertical handling of pipets)
ii. operator variables (technical competencies)
iii. instrument instability (pipet tips not fitting properly, clogged pipets, imprecise pipets, pipet contamination)
iv. temperature and timing variations
v. reagent variation (air bubbles in reagent)
vi. power supply fluctuations

Question 4

These are systematic change in the test system that displaces the mean of distribution from its original value. It significantly affects the accuracy of the test system. It is predictable and causes shifts or trend on control charts. The term inaccuracy and bias often are used to emphasize the lack of agreement among methods being compared. This error is detected as either positive or negative bias for a given analytical method. It can be classified as either a constant error or proportional error.

Answer 4

Systematic Errors

Question 5

Systematic Errors: Constant or Proportional?

• show constant difference between comparative method and test method. The magnitude of error is constant and error is NOT
  dependent on analyte concentration

Answer 5

Constant errors

Question 6

Systematic Errors: Constant or Proportional?

• also known as slope or percent error. In this type of systematic error, the magnitude of error changes as a percent of analyte. The error is dependent on analyte concentration.

Answer 6

Proportional errors

Question 7

Common causes of systematic errors include:

Answer 7

i. Equipment non-reliability which results from change of temperature in incubators or reaction blocks, deterioration of a photometric light source and change in sample volumes due to pipette mis adjustments or misalignments.
ii. Reagent and Calibrator changes which include changes in reagent or calibrator lot numbers, use of wrong calibrator values, improperly prepared reagents, deterioration of reagents or calibrators and inappropriate storage of reagents and calibrators.
iii. Changes in procedure from one performer to another.
iv. Errors in specificity, precision and accuracy

Question 8

The combination of random
errors and systematic errors are
collectively referred to as _____________

Answer 8

TOTAL ERROR