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QUALITY CONTROL

QUALITY CONTROL. QUALITY CONTROL.

Quality management

Quality assurance

Quality control

Three principles of clinical lab

What is Quality?

Quality defined as conformance to the

requirements of users or customers

Total quality management of the clinical lab

Quality planning

Quality lab process

Quality control

Quality assessment

Quality improvement

Quality Control

Quality control

Emphasizes statistical and nonstatistical check procedures

Able to detect the problems early enough to prevent their consequences

Techniques and procedures that monitor performance parameters

Prerequisite for an effective lab service

Promotion of quality control and continuous

improvement of the total testing process, including

preanalytical and postanalytical phases

Test is requested by physician and ordered on the computer. Barcode is generated Specimen is collected

Specimen and order are transported to the lab

The specimen is accessioned in the lab

The specimen is processed

The specimen is analyzed

The results are reviewed and verified & dispatched

Steps in obtaining a laboratory test

Lab testing processes and their potential errors

Test ordering Specimen acquisition

Analytical measurement Test reporting Test

interpretation

Test ordering

Inappropriate testHandwriting not

legibleWrong patien

t identification

Specimen acquisition

Analytical measurem

entTest

reportingTest

interpretation


Test ordering

Specimen acquisitionIncorrect tube

Incorrect

patient identific

ationInadequ

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d at wrong time

Improper

transport

conditions

Analytical measurem

entTest

reportingTest

interpretation


Test ordering


Analytical

measurement

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Test reporting

Test interpretat

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Test ordering


Analytical measurem

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Test interpretat

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Test ordering


Analytical measurem

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Test reporting

Test interpretationInterferin

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dSpecificity

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Precision limitation

s not recognize

dAnalytical sensitivity

not appropria

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values not

available for

comparison


Elements of a QA/QC Program

Commitment

Facilities and resources

Technical competenceTechnical procedures

Problem solving mechanisms

Quality Control: Technical Procedures

Control of preanalytical variables

Control of analytical variables

Control of analytical quality using statistical methods and control charts

Test requests

Patient preparation

Patient identification


Control of preanalytical variables

HOW TO CONTROL THESE ERRORS?

Patient Identification The highest frequency of errors occurs with the use of handwritten labels and request forms.

The use of bar code technology has significantly reduced ID problems.

Turnaround timeDelayed and lost test requisitions, specimens and reports can be major problems for labs.

Recording of the actual times of specimen collection, receipt in the lab and reporting of results with use of computers will solve these problems.

PRE ANALYTICAL VARIABLES



Transcription error Manual entry of data even with the double checking of results

Computerization will reduce this type of transcription error.

Patient preparation Lab tests are affected by many factors, such as, recent intake of food, alcohol, or drugs; smoking, exercise, stress, sleep, posture during specimen collection

The lab must define the instructions and procedures compliance with these instructions can be monitored directly efforts should be made to correct non compliance



Specimen Collection

• Prolonged tourniquet application. • Blood collection from an arm into which an intravenous infusion is running.

Hemolysis during blood collection

• To monitor and control these problems, specially trained lab team assigned to specimen collection

• The identification of the person collecting a specimen should be maintained • Clinicians should be encouraged to report clinically inconsistent results.

Analytical methodology

Standardization

Calibration procedures

Documentation of analytical protocols

Monitoring of critical equipment and materials

Control of analytical variables


CONTROL OF ANALYTICAL VARIABLES

Many analytical variables

• Water quality• Calibration of volumetric glassware and pipets• Stability of electrical power• Stability of temperature of heating baths, refrigerators, freezers and centrifuges



The procedure Manual should contain the following

• Procedure name• Clinical significance• Principle of method• Specimen of choice• Reagents and equipments



The procedure Manual should contain the following

•• Procedure• Reference values• Comments• References



Using stable ‘controls’

• Values cover medical decision points • Similar to the test specimen (matrix)• Available in large quantity• Stored in small aliquots• Ideally, should last for at least 1 year

QC material- Preparation & Storage

Precautions to be followed

• Reconstitute lyophilized material carefully & strictly as per label direction• Frozen sample to be thawed properly. After attaining room temp., mix slowly

by inversion and then use.• Storage temperature to be strictly followed

QC material Availability

Assayed

Unassayed

Level 1 , 2 and 3



Using ‘Calibrators’

• Have a known concentration of the substance (analyte) being measured • Used to adjust instrument, kit, test system in order to standardize the assay• Sometimes called a standard, although usually not a true standard • This is not a control

Quantitative Aspects of QC

External Q C

Internal Q C

Internal Q C

Day to day internal QC programme

Is a most useful tool

For maintenance of long term Consistency ( Accuracy ) control

Long term Precision control of analytical method

Internal Q C monitors a single lab

External Q C

Provides independent validation of internal QC program

Gives valid estimation of long term accuracy of analytical system

Compares performance of different labs

Control of analytical quality using statistical methods and control charts

Statistical methods

Mean, SD, CV

Accuracy

Precision

Control charts

Levey-Jennings Control Chart

Westgard multirule chart

Shewhart SD control chart

Good Accuracy Good Precision

Good Precision Only

Neither Good precision Nor Accurate

Frequency of observation

Control limit

Control limit

Stable performance Accuracy problem Precision problem

Obs

erve

d co

ntro

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cent

ratio

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l

Time

Control limit

Control limit


Obs

erve

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Trends & Shifts

Strandard Deviation

• In statistics and probability theory, the standard deviation (SD) (represented by the Greek letter sigma, σ) shows ;

• how much variation or dispersion from the average exists.

http://en.wikipedia.org/wiki/Statistics

http://en.wikipedia.org/wiki/Probability_theory

http://en.wikipedia.org/wiki/Sigma

http://en.wikipedia.org/wiki/Statistical_dispersion

Strandard Deviation

• A low standard deviation indicates that the data points tend to be very close to the mean (also called expected value)

• A high standard deviation indicates that the data points are spread out over a large range of values

http://en.wikipedia.org/wiki/Mean

Strandard Deviation

coefficient of variation

• The coefficient of variation (CV) is defined as the ratio of the standard deviation to the mean

http://en.wikipedia.org/wiki/Standard_deviation

http://en.wikipedia.org/wiki/Mean

Levey-Jennings chart

• Levey-Jennings chart is a graph that quality control data is plotted on to give a visual indication whether a laboratory test is working well

• The distance from the mean is measured in standard deviations (SD)

http://en.wikipedia.org/wiki/Quality_control


• On the x-axis the date and time, or more usually the number of the control run, are plotted.

• A mark is made indicating how far off the actual result was from the mean (which is the expected value for the control).


• Lines run across the graph at the mean, as well as one, two and sometimes three standard deviations either side of the mean.

• This makes it easy to see how far off the result was.

Control of analytical quality using patient data

Clinical correlation of test results Correlation with other lab tests

45

Selecting Control MaterialsCalibrators

Selecting Control MaterialsCalibrators

• Has a known concentration of the substance (analyte) being measured

• Used to adjust instrument, kit, test system in order to standardize the assay

• Sometimes called a standard, although usually not a true standard

• This is not a control

• Has a known concentration of the substance (analyte) being measured

• Used to adjust instrument, kit, test system in order to standardize the assay

• Sometimes called a standard, although usually not a true standard

• This is not a control

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Selecting Control Materials Controls

Selecting Control Materials Controls

• Known concentration of the analyte Use 2 or three levels of controls Include with patient samples when

performing a test• Used to validate reliability of the test system

• Known concentration of the analyte Use 2 or three levels of controls Include with patient samples when

performing a test• Used to validate reliability of the test system

Biological Specimens

• Blood • Urine• Cerebrospinal Fluid• Amniotic Fluid • Duodenal Aspirate• Gastric Juice• Gall stone• Kidney Stone• Stools• Saliva• Synovial Fluid• Tissue Specimen

• Choice of specimen type depends on– Analyte to be measured – Ease of collection

Comprise the majority of all specimens analyzed

Blood Composition

Plasma

Plasma is fluid component of blood.Comprises ~55% of total volume of whole blood. Contains proteins, sugars, vitamins,minerals, lipids, lipoproteins andclotting factors. 95% of plasma is water

Red Blood cells (RBC)

Whole Blood Whole Blood after centrifugationNote: clotting has been prevented

White Blood cells (WBC) & Platelets Cellular

Components

Blood Composition

Serum

Plasma is fluid component of blood.Comprises ~55% of total volume of whole blood. Contains proteins, sugars, Vitamins,,minerals, lipids, lipoproteins No clotting factors95% of plasma is water

Blood Clot-comprised of clotting factors (Fibrin,platets etc)-RBCs

Whole Blood Whole Blood after clotting and centrifugation

If blood is collected and allowed to stand it will clot. Formation of an insoluble fibrin clot. If blood is then centrifuged the fluid portion is known as SERUM

Blood Analysis• Source

– Veins – Arteries– Skin puncture-capillary blood

• Factors affecting choice of Blood Source and Collection Method– Analyte under investigation– Patient

• vascular status• ease of collection

• Collection Method– Syringe– Evacuated tube

• Additives• Separator gel

– Intravenous lines

Blood Analysis• Testing can be done on whole blood, serum or plasma. Choice depends on a

number of factors• Analyte to be measured

– Most hematology tests requires whole blood

• Instrumentation used for analysis– Most automated instruments are not set up for whole blood

analysis

• The way the test was developed. – Tests are often only validated on either plasma or serum

• Turn around time– Analysis of whole blood is the quickest. No waiting for clot or

spinning– Plasma requires centrifugation prior to analysis– With serum, the blood must clot then you have to centrifuge

Blood Analysis in the Chemistry

• Since most tests in the chemistry lab involve analytes that are dissolved in the fluid portion of blood, serum or plasma are the specimens of choice.

• Important exceptions include– Hemoglobin, Red blood cell (RBC) Folate– Blood gases

• Protein electrophoresis was developed based on the analysis of serum. Not done on plasma because of the presence of the protein fibrinogen which distorts the electrophoretic pattern.

• Many tests can use either serum or plasma

Collection Tubes• The most widely used tubes for blood collection

are evacuated tubes (Vacutainers)– Negative pressure facilitates collection– Easy to use– Sterile– Universally used colour-coded rubber stoppers to

denote tube type.– Tubes can contain various anticoagulants for the

collection of whole blood or plasma.– Tubes can have additives for specific tests (glucose,

metals)

Collection Tubes(Vacutainers)

Serum Separator Tube (SST)

Separator Gel

Separator Gel

Serum

Clot

Collection tubes

• Red-top tubes contain no anticoagulants or preservatives

• Red-top tubes are used for collecting serum– 10-15 minutes is required to allow blood to clot

before centrifuging– Used for blood bank specimens, some

chemistries

Collection tubes

• Gold (and “tiger”) top tubes contain a gel that forms a physical barrier between the serum and cells after centrifugation

• No other additives are present• Gel barrier may affect some lab tests

Collection tubes

• Used for Glucose measurement. • After blood collection, glucose concentration decreases

significantly because of cellular metabolism• Gray-top tubes contain either:

– Sodium fluoride and potassium oxalate, or– Sodium iodoacetate

• Both preservatives stabilize glucose in plasma by inhibiting enzymes of the glycolytic pathway– NaF/oxalate inhibits enolase– Iodoacetate inhibits glucose-3-phosphate dehydrogenase

Collection tubes

• Green-top tubes contain either the Na, K, or lithium (Li) salt of heparin. Most widely used anticoagulant for chemistry tests.– Should not be used for Na, K or Li measurement– Can effect the size and integrity of cellular blood components and

not recommended for hematology studies• Heparin accelerates the action of antithrombin III, which

inhibits thrombin, so blood does not clot (plasma)• The advantage of plasma is that no time is wasted waiting

for the specimen to clot

Collection tubes

• Lavender-top tubes contain the K salt of ethylenediaminetetraacetic acid (EDTA), which chelates calcium (essential for clot formation) and inhibits coagulation

• Used for hematology, and some chemistries• Cannot be used for K or Ca tests

Collection tubes

• Blue-top tubes contain sodium citrate, which chelates calcium and inhibits coagulation

• Used for coagulation studies because it is easily reversible.

Collection tubes

• Brown and Royal Blue top tubes are specially cleaned for trace metal studies– Brown-top tubes are used for lead (Pb) analysis– Royal blue-top tubes are used for other trace

element studies (acid washed)

Test results

Variations, Errors, Interferences • Variations• Clinical variations within an individual and

between individuals• Analytical variations-no test is perfect. All tests

have some degree of variations for repeated measurements of the same sample.

• The final test result is affected by factors that occur – Pre-analytically– At the time of the test– After the test is completed


• Test is requested by physician and ordered on the computer. Barcode is generated

• Specimen is collected

• Specimen and order are transported to the lab

• The specimen is accessioned in the lab


• The specimen is processed

• The specimen is analyzed

• The results are reviewed and verified by technologists

• The results are released to the patient’s record

Why Analytical Results VaryInter-individual

Variation • Age• Sex• Race• Genetics• Long term health status

Intra-individual Variation •Diet•Exercise•Drugs•Sleep pattern•Posture•Time of venipucture•Length of time tourniquet is applied

Why Analytical Results VaryPre-analytical Variation •Transport•Exposure to UV light•Standing time before separation of cells•Centrifugation time•Storage conditions

Analytical Variation •Random errors•Systematic errors

Post-analytical •Transcriptions errors•Results reported to wrong patient

Pre-analytical errors

• Collection– Was the right tube used?– Was venipuncture performed correctly?– Was the specimen properly stored?

• Identification– Was the blood collected from the correct

patient?– Was the blood correctly labeled?

• Patient name, ID, date, time of collection, phlebotomist

Specimen identification

• One of the common sources of erroneous lab results is misidentified specimens

• The lab is required to have a clear and rational policy for identifying specimens, and handling misidentified specimens

Prolonged venous stasis

Blocking the flow of blood with the tourniquet with eventually lead to a sieving effect. Small molecules, water and ions are forced out blood vessels and larger molecules are concentrated

• Increases Total Protein, proteins, iron (Fe), cholesterol, bilirubin

• Decreases potassium

Supine vs. sitting or standing

• Going from lying (supine) to upright reduces total blood volume by about 700 ml

• The following may decrease by 5-15% in the supine patient:– Total protein– Albumin– Lipids– Iron– Calcium– Enzymes

Specimens requiring special handling

• Should be placed immediately on ice– Lactate– Ammonia– Acid phosphatase– Plasma catecholamines

Significantly affected by hemolysis:

• Hemolysis-rupture of red blood cell– Can be due to improper collection – End result is dumping cellular contents into

blood. Mild dilution effect in some analytes

• Significant increase in potassium, magnesium, phosphorous

Interferences• Hemolysis

– The release of hemoglobin into blood can effect the reactions comprising specific tests

– Causes serum or plasma to be red and can effect tests that are colorimetric

• Lipemia (lots of fats) and proteinemia (lots of protein)– Causes serum or plasma to be become turbid. This can

effect colorimetric and turbidometric based tests– Also can cause a dilution effect. Fats and proteins are

large and displace water in plasma. Can give falsely low results especially for Na

Interferences• Human Anti Animal Antibodies.

– Occurs in individual that have been exposed to foreign immunoglobins

– Can significantly increase or decrease immunoassay based tests since all utilize animal antibodies, particularly mouse. Referred to as Human Anti Mouse Antibodies (HAMA)

– Tests usually contain reagent to clear HAMA– Technicians performs a dilution test to determine if

HAMA are present– Generally have to send to another lab to test by alternate

method or different antibody

l

Time

Control limit

Control limit


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Trends & Shifts

Run numbers

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Mean

+1s

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+2s

-2s

-1s

-3s

Westgard Multirule Chart

0 1 2 3 4 5 6 7 8 9 10………………………………………30

Run numbers

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+1s

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0 1 2 3 4 5 6 7 8 9 10………………………………………30

12sWarning rule

Run numbers

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+1s

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0 1 2 3 4 5 6 7 8 9 10………………………………………30

13sRejection rule

Run numbers

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+1s

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0 1 2 3 4 5 6 7 8 9 10………………………………………30

22sRejection rule

Run numbers

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+1s

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R4sRejection rule

Run numbers

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+1s

+3s

+2s

-2s

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0 1 2 3 4 5 6 7 8 9 10………………………………………30

Rejection rule41s

Run numbers

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+1s

+3s

+2s

-2s

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0 1 2 3 4 5 6 7 8 9 10………………………………………30

Rejection rule10 x

CUSUM Control Chart

Control of analytical quality using patient data

Clinical correlation of test results Correlation with other lab tests

References

• Tietz test book of clinical Biochemistry• Varley• Kaplan• Internet

Science

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