QUALITY CONTROL Flashcards by V S

Ability of analytical method to measure the smallest concentration of analyte

Sensitivity

How well did you know this?

Not at all

Perfectly

Ability of analytical method to measure only the analyte of interest

Specidicity

How well did you know this?

Not at all

Perfectly

Nearness or closeness of the assayed value to the true or target value

Accuracy

How well did you know this?

Not at all

Perfectly

Ability of analytical method to give repeated results on the same sample

Precision or Reproducivility

How well did you know this?

Not at all

Perfectly

Degree by which a method is easily repeated

Practicability

How well did you know this?

Not at all

Perfectly

Ability to maintain accuracy and precision over an extended period of time

Reliability

How well did you know this?

Not at all

Perfectly

Ability of analytical method to detect proportion of individuals without the disease

Diagnostic Specificity

How well did you know this?

Not at all

Perfectly

Ability of analytical method to detect proportion of individuals with the disease

Diagnostic Sensitivity

How well did you know this?

Not at all

Perfectly

Sensitivity (%)

100 x number of true positive / total number of diseased

How well did you know this?

Not at all

Perfectly

Specificity (%)

100 x number of true negative / total number of without disease

How well did you know this?

Not at all

Perfectly

Error due to chance, varies from sample to sample

Random Error

How well did you know this?

Not at all

Perfectly

Due to instrument, operator and environmental conditions such as:
> pipetting error
> mislabeling of samples
> temperature fluctuation
> improper mixing of sample and reagent

Random Error

How well did you know this?

Not at all

Perfectly

Error that influences observations consistently in one direction

Systematic Error

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Difference between the target value and the assayed value

Constant Error

How well did you know this?

Not at all

Perfectly

Results in greater deviation from the target value due to higher sample concentration

Proportional/ Slope/ Percent Error

How well did you know this?

Not at all

Perfectly

Highest frequency of Clerical errors occurs with

Use of handwritten labels and Request forms

How well did you know this?

Not at all

Perfectly

Objectives of Quality Control

Check stability of the machine
Check quality of reagents
Check technical errors

How well did you know this?

Not at all

Perfectly

Levels of control solutions in General Chemistry

TWO levels

How well did you know this?

Not at all

Perfectly

Levels of control solutions in Immunoassays

THREE levels

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

Most laboratory errors occur in:

Pre-Analytic and Post-Analytic stages

Occurs when the data set can be accurately described by the SD and the MEAN obtained by plotting the values from multiple analyses of a sample

Gaussian Curve/ Bell-Shaped Curve

Calculates the difference between QC results and the target means Identifies consistent bias problems Very sensitive to small persistent errors that commonly occur in the modern, low calibration-frequency analyzer

Cumulative Sum Graph (CUSUM)

Used to compare results obtained on a high and low control serum from different laboratories

Youden/ Twin Plot

Most widely used QC chart in the clinical laboratory Allows the laboratorians to apply multiple rules without the aid of a computer Easily identifies random and Systematic Errors

Shewhart Levey-Jenning Chart

Error in LJ Chart: formed by control values that either increase or decrease for 6 consecutive days MC: Deterioration of reagents

Trend

Error in LJ Chart: formed by control values that distribute themselves on one side or either side of the mean for 6 consecutive days MC: Improper calibration of the instrument

Shift

Error in LJ Chart: control values that are far from the main set of values highly deviating values caused by random or systematic errors

Outliers

Recognizes that the use of simple upper and lower control limits is not enough to identify analytical problems

Westgard Control Chart

Used as a rejection or warning rule when one control result exceeds the mean +-2SD

1 2s

Observed when one control result exceed the mean +- 3SD due to RANDOM error

1 3s

Observed when last 2 control results exceed either the mean +- 2 SD due to SYSTEMATIC error

2 2s

Last four consecutive control results exceeds either mean +- 1SD due to SYSTEMATIC error

4 1s

Range of difference between the highest and lowest control result within an analytical run exceeds 4s due to SYSTEMATIC error

R 4s

Westgard test method

at least 40 samples

Westgard Reference method

at least 100 samples

Acceptable reference limit is set at

+- 2SD or 95%

Set of control and patient specimen assayed, evaluated and reported together

Analytical run

Most commonly used patient based-QC techniques Difference between two consecutive measurements of the same analyte on the same individual

Delta check

Used to measure systematic errors or inaccuracy caused by substances other than the analyte

Interference experiments

Concentration range over which the measured concentration is equal to the actual concentration without modification of the method

Linear range/ Dynamic Range

Sometimes referred to as absurd value Helps detect sample contamination or dilution, inadequate sample volume, inadequate reagent volumes, sudden major problems with the method, or incorrect recording or transmission of the result

Physiologic Limit

Type of analytical testing performed outside the confines of the central laboratory, usually by nonlaboratorian personnel

Point Of Care Testing (POCT)/ Decentralized Testing

Most commonly used POCT

Use of portable whole blood glucose meters for the management of patients with diabetes mellitus

Systematic Action necessary to provide adequate confidence that laboratory services will satisfy the given medical needs for the patient

Quality Assurance

Can be envisioned as a tripod with three legs

Program development Assessment and Monitoring Quality Improvement

Primary Goal of QA

To deliver quality services and products to customers

Includes effective test request forms, Clear instruction for patient preparation and specimen handling, appropriate turn-around time for specimen processing, testing and result reporting, appropriate reference ranges and intelligent result reports

Quality Patient Care

Probability that a positive test indicates disease

Positive Predictive Value

Probability that a negative test indicates absence of disease

Negative Predictive Value

Formula PPV:

TP/ TP+FP

Formula NPV:

TN/TN+FN