2. QUALITY CONTROL

Quality Assurance (QA)

A comprehensive system of policies and procedures that ensures reliable laboratory results by preventing errors throughout the testing process.

Standard Operating Procedures (SOPs)

Written instructions that standardize laboratory procedures to ensure consistent and reliable results.

Quality Control (QC)

A component of Quality Assurance that monitors the accuracy and precision of laboratory testing using quality control materials.

Quality Control Materials

Materials with known values used to monitor QC or the accuracy and precision of laboratory tests.

Reference Materials

Materials used solely to calibrate laboratory instruments and equipment.

Total Quality Management (TQM)

Refers to the overall process used to ensure that laboratory results meet the requirements for health care services to patients

Control limits

s the acceptable range of values that a QC result should fall within.

±2 SD

The ideal QC control limit is _____

Levey-Jennings Chart

is the most commonly used quality control chart in the laboratory.

2

• Level 1 = Normal

• Level 2 = Abnormal

General chemistry tests usually use __ levels of control.

3

• Level 1 = low control

• Level 2 = normal control

• Level 3 = high control

Immunoassays commonly use __ levels of control.

lyophilized

Most commercially prepared QC materials are _____________

● To check the stability of the machine

● To check the quality of the reagents

● To check technical (operator) errors

ENUMERATE

OBJECTIVES OF QUALITY CONTROL

College of American Pathologists (CAP) proficiency program

It is considered the gold standard for External Quality Control in clinical laboratories.

National Reference Laboratories (NRLs)

are the DOH-designated EQAS providers.

Department Order No. 393-E s. 2000

According to ____________________________, the DOH designated five National Reference Laboratories (NRLs).

Lung Center of the Philippines (LCP)

NRL for Clinical Chemistry

San Lazaro Hospital /STD-AODS Cooperative Central Laboratory (SLH/SACCL)

NRL for Immunology/Serology and HBsAg, HIV, HCV

East Avenue Medical Center (EAMC)

NRL for Toxicology, Occupational and Environmental Health and Micronutrient Assay. Drugs of abuse (methamphetamine and cannabinoids)

National Kidney and Transplant Institute (NKTI)

NRL for Hematology and Coagulation

Research Institute for Tropical Medicine

NRL for Microbiology (identification and antibiotic susceptibility testing) and Parasitology (identification of ova and quantification of malaria)

● Glucose

● Blood Urea Nitrogen (BUN)

● Creatinine

● Uric Acid

● Cholesterol

● Total Protein

● Albumin

● Sodium

● Potassium

● Chloride

10 ANALYTES BEING QUANTIFIED FOR NEQAS CLINICAL CHEMISTRY

Sensitivity

Ability of the analytical method/process to detect the smallest concentration of analyte of interest

Specificity

Ability of an analytical method to measure only the specific analyte of interest

Accuracy

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

Precision or Reproducibility

Ability of an analytical method to give repeated results on the same sample that agree with one another

Practicability

Degree by which a method is easily repeated

Reliability

Ability of an analytical method to maintain accuracy and precision over an extended period of time during which equipment, reagents, and personnel may change

True Positive

A patient has the disease or condition and is positive on the test

False Negative

the patient has the disease or condition but is negative on the test

Diagnostic Specificity

Ability of a test to correctly identify the absence of a given disease or condition

True Negative

the patient does not have the disease or condition and is negative of the test

False Positive

the patient does not have the disease or condition but is positive of the test

Diagnostic Sensitivity

Ability of a test to detect a given disease or condition

formula for Diagnostic Sensitivity

formula for Diagnostic Specificity

RANDOM ERROR

Present in all measurements; due to chance

RANDOM ERROR

this is a type of error due to instrument, operator, environmental conditions such as pipetting error, mislabeling in samples, temperature of analyzer (fluctuations in temperature), and improper mixing of sample or reagent

SYSTEMATIC ERROR

Error always in one direction. It is detected as either positive or negative bias

SYSTEMATIC ERROR

type of error that is often related to calibration problems, deterioration of reagents and control materials, improperly made standard solutions (for calibrations of analyzers in the laboratory), contaminated solutions, unstable and inadequate reagent blanks, leaky ion selective electrode (ISE, or in case you are using ISE to measure patient’s electrolytes), poorly written solutions

• Constant error

• Proportional Error (Slope/Recent Error)

ENUMERATE

types of systematic error

Constant error

The magnitude of change is constant and not dependent on amount of analyte.

Cause: interference or contamination

Proportional Error (Slope/Recent Error)

Error dependent on analyte concentration

Cause: poor recovery of analyte during an analysis

a. acceptable

if RE and SE (total error) < Ea, the performance of the test is considered ______________

a. acceptable

b. rejected

b. rejected

if RE and SE (total error) > Ea, the performance of the test is considered ______________

a. acceptable

b. rejected

less than 1%

Highly precise analyzers often have a CV of ___________.

Mean

The average of a set of values and the most commonly used measure of central tendency.

Standard Deviation

The most commonly used measure of variation that indicates how far values are dispersed from the mean

formula for SD

False

T or F

The lower the SD, it’s farther to the mean or the average value

Coefficient of Variation (CV)

An index of precision that expresses variability as a percentage

Variance

A measure of variability equal to the square of the standard deviation (SD²).

formula of CV

68.3%

______ of the values under the normal curve is between ± 1SD

95.4%

_____ of the values would fall under ± 2SD control limits

99.7%

____ under the normal curve is between ± 3SD

Westgard Rules

Decision rules applied to the Levey-Jennings Chart to determine whether a QC run should be accepted or rejected.

Cumulative Sum (CUSUM) Graph

A QC chart used for the early detection of systematic errors.

Youden / Twin Plot

A QC chart used to identify proportional and constant analytical errors.

TREND

A QC pattern in which control values continuously increase or decrease for 6 consecutive days and cross the mean.

Main cause: deterioration of reagents

SHIFT

A QC pattern in which 6 consecutive control values remain on the same side of the mean.

Main cause: improper calibration of the instrument

(1) QC values continuously increase or decrease for 6 consecutive days, and

(2) the values pass the mean.

Criteria for a Trend

OUTLIERS

○ Are values that are far from the main set of values

○ Are highly deviating values

○ Caused by R/S errors

Yes

if the control value is seen outside the +2S, is it still classified as 12s rule violation?

12s

1 is the control rule, indicates the number of control observations per analytic run

1_3s + R_4s

what are the westgard rules that indicate random error?

2_2s + 4_1s + 10x

what are the westgard rules that indicate systematic error?

1₂s

One control observation exceeds the mean ±2 SD; a warning rule used for screening that prompts evaluation using other Westgard rules.

1₃s

One control observation exceeds the mean ±3 SD, indicating a random error.

2₂s

Two consecutive control observations exceed the same mean ±2 SD limit, indicating a systematic error.

4₁s

Four consecutive control observations exceed ±1 SD on the same side of the mean, indicating a systematic error.

R₄s

The difference between the highest and lowest QC result within the same analytical run exceeds 4 SD (one above +2 SD and one below −2 SD), indicating a random error.

10x

Ten consecutive control observations fall on the same side of the mean, indicating a systematic error.