QUALITY ASSURANCE

Quality Assurance

A complete system of creating and following procedures and policies to aim for providing the most reliable patient laboratory results and to minimize errors in the pre-analytical, analytical, and post-analytical phases

Quality Control

An aspect of QA that is used to assess the analytical phase of patient testing

Accreditation

The process by which an agency or an organization evaluates and recognizes a program of study or an institution as meeting certain predetermined qualifications or standards; applies only to institutions and program

Pre-analytical phase

Patient preparation and considerations

Pre-analytical phase

Time of collection

Pre-analytical phase

Specimen collection order

Pre-analytical phase

Quality of specimen collected

Pre-analytical phase

Specimen processing, storage, and preservation

Fasting

For TDM, glucose

Monitors baseline/ basal state

Time of collection

Monitor TAT (turn-around-time)

Time of collection

For analytes that exhibit diurnal variation (e.g. cortisol)

TDM peak sample

Collected 30-60 mins AFTER dose

TDM trough sample

Collected BEFORE next dose

1. Blood culture

2. Na Citrate

3. Serum

4. Heparin

5. EDTA

6. Na Fluoride

Specimen collection order

SPS/ Yellow top

Blood Culture

1. Light blue top

2. Black top

Na citrate

Light blue top

For coagulation studies

Black top

For ESR

Black top

Westergren OG

EDTA

Westergren Mod

1. Red top

2. Gold top

Serum

Red top

For chemistry & serology

Green top

Heparin

Green top

For electrolyte analysis

Green top

EOFT (Erythrocyte Osmotic Fragility Test)

Green top

For blood gas (arterial blood)

Lavander, pink, white, tan top

EDTA

Lavander, pink, white, tan top

For hematology (CBC) & chemistry (HBA1C)

Gray top

Na Fluoride

Gray top

For glucose analysis

Bilirubin

Photo-labile analyte

LD4, LD5

Cold-labile analytes

1. Mean

2. Median

3. Mode

Measures of Central Tendency

Mean

Obtained by adding all the numbers in the set and dividing the sum by the number of values in that set; also known as average

Mean

Reflects accuracy

Median

Middle value in a set of numbers that are arranged into an array

Median

Arranged according to their magnitude, i.e. highest to lowest or lowest to highest

Mode

Most frequently obtained value in a set of numbers

1. Standard Deviation

2. Coefficient of Variation

Measures of Dispersion or Scatter

Standard Deviation

Reflects the variation of data values around the mean

Standard Deviation

Indicator of precision

Coefficient of Variation

Reflects random variation of analytical methods in units that are independent of the method

Coefficient of Variation

Relative indicator of precision

Gaussian Distribution Curve

Bell-shaped curve

Mean = Median = Mode

Normal distribution curve

68.3%

Inside ± 1SD =

31.7%

Outside ± 1SD =

95.5%

Inside ± 2SD =

4.5%

Outside ± 2SD =

99.7%

Inside ± 3SD =

0.3%

Outside ± 3SD =

1. t-test

2. F-test

Tests for Statistical Significance

t-test

Used to test for significant differences between two means

t-test

Help evaluate accuracy

F-test

Used to test for significant differences between two variances or SD

F-test

Help evaluate precision

Statistical Binary Classifiers

Used to determine diagnostic/ analytical efficiency

1. Diagnostic Sensitivity

2. Diagnostic Specificity

3. Positive Predictive Value

4. Negative Predictive Value

Statistical Binary Classifiers

Diagnostic Sensitivity

The percentage of persons who have a given disorder who are identified by the assay as (+) for the disorder

Diagnostic Sensitivity

(TP/ TP + FN) x 100

Diagnostic Specificity

The percentage of persons who do not have a given condition who are identified by the assay as (-) for the condition

Diagnostic Specificity

(TN/ TN + FP) x 100

Positive Predictive Value

The probability that subjects with a (+) screening test truly have the disease

Positive Predictive Value

(TP/ TP + FP) x 100

Negative Predictive Value

The probability that subjects with a (-) screening test truly don't have the disease

Negative Predictive Value

(TN/ TN + FN) x 100

Reliability

Refers to the ability of the analytical method to maintain accuracy and precision over an extended period of time

Accuracy

The closeness of the assayed value to the true/target value

Precision

The closeness of the assayed value to a repeated value

1. Repeatability

2. Reproducibility

Precision

Repeatability

Closeness of agreement between results of successive instruments carried out under the same conditions

Reproducibility

Closeness of agreement between results of measurements performed under changed conditions

Analytical Sensitivity

Ability of the method to detect small quantities of the measured analyte

Analytical Sensitivity

An aspect of precision

Analytical Specificity

Ability of the method to measure only the analyte for which it is designed to detect

Analytical Specificity

An aspect of accuracy

Practicability

The degree to which a method is easily repeated

Standard

Material of known concentration, used to calibrate instrument

Internal/ Intralab Quality Control

Performed by laboratory personnel using controls of known values and comparing the control values to established acceptable ranges

External Quality Control

Performed by laboratory personnel when analyzing specimens sent to the laboratory by an external agency; results generated are submitted to the agency for assessment – a process known as Proficiency Testing

Control

Also known as serum pool or pooled sera

Control

Material of known value that is analyzed with patient samples to determine acceptability of results

Control

Resembles patient specimen

Qualitative

(+) control and (-) control

Tri-level

normal control, ↓ control, ↑ control

Levey Jennings Control Chart

Commonly used in the laboratory quality control

Levey Jennings Control Chart

Also known as U chart or Shewhart plot

Independent variable — date/ time

Levey Jennings Control Chart x-axis

Dependent variable — concentration

Levey Jennings Control Chart y-axis

1. Systematic Error

2. Random Error

Types of Errors

Systematic Error

Appear with pattern; predictable

Random Error

Appear due to chance; unpredictable

Shift

Sudden or abrupt change in the data, which establishes a new distribution pattern above or below the established mean

Shift

6 or more consecutive daily values that distribute themselves on a side of the mean value line, but maintain a constant level

Trend

Gradual deviation in the data above or below the mean

Trend

Values for the control that continue to either increase or decrease over a period of 6 consecutive days

Outliers

Value(s) that are far from the usual set

R_4s

1_2s

1_3s

2_2s

4_1s

10_x

Westgard Multirules

Delta Check

Change check; Compares current vs previous results

< 40 mg/dL

> 500 mg/dL

Critical/ Panic/ Alert Values for glucose