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مشروع إعتماد معمل الكمياء الإكلينيكيه – مستشفى الطوارئ. Prof/ Azza abd al baky. Role of clinician in lab result accuracy. Introduction. Three phases of laboratory testing: pre-analytical, analytical and post-analytical

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slide2

مشروع إعتماد معمل الكمياء الإكلينيكيه – مستشفى الطوارئ

role of clinician in lab result accuracy

Prof/Azzaabd al baky

Role of clinician in lab result accuracy

introduction
Introduction
  • Three phases of laboratory testing: pre-analytical, analytical and post-analytical
  • Pre-analytical—specimen collection, transport and processing
  • Analytical—testing
  • Post-analytical—testing results transmission, interpretation, follow-up, retesting.
pre analytical errors
Pre-analytical errors
  • Pre- and post-analytical errors are estimated to constitute 90% of errors
  • Errors at any stage of the collection, testing and reporting process can potentially lead to a serious patient misdiagnosis
  • Errors during the collection process are not inevitable but can be prevented with a diligent application of quality control, continuing education and effective collection systems.
the steps of the preanalytical phase
The steps of the preanalyticalphase

Preparation prior to

sampling

Sampling/handling

Storage/transport

Preparation prior to analysis

implications of errors
Implications of errors
  • and compromise the diagnosis and treatment of the patient
  • Errors made in the period prior to the analysis of the sample ...
  • may influence the quality of the final measured results ...

No result is better than bad result

complex and labor intensive
Complex and labor intensive
  • The more steps involved in a process, the more likely there will be errors committed
  • 32 - 75% of all test errors occur in the preanalytical phase

Stankovic 2008

“Quality Improvements in the Preanalytical Phase:

Focus on Urine Specimen Workflow”

effects of pre analytical variables on the quality of laboratory testing
Effects of Pre-analytical Variables on the Quality of Laboratory Testing
  • Paying close attentionto the preanalyticalvariables associated with blood collection iscriticalin ensuring accurate testresults in all areas of the clinical laboratory.
the pre analytical process
The Pre-Analytical process
  • Patient Identification
  • Sampling Technique
  • Test Collection Procedures
  • Specimen Transport
  • Specimen Processing
the pre analytical process1
The Pre-Analytical process

Collect Sample:

  • Locate Patient
  • Prep Patient
  • Draw Sample
  • Label
  • Dispose of supplies
patient identification
Patient identification

When identifying the patient, have them provide their full name, address, identificationnumberand/or date of birth. Hospital No inpatients should be wearing an identification band with the above information, which the phlebotomist should confirm before the venipuncture.

effects of pre analytical variables on the quality of laboratory testing1
Effects of Pre-analytical Variables on the Quality of Laboratory Testing
  • Patient Identification:It is important to identify a patient accurately so that blood is collected from the correct person. Drawing blood from the wrong person, or labeling the correct patient’s sample with a different patient’s label can certainly contribute to laboratory error. (Mislabeling ???)
factor affecting lab result
Factor affecting lab result
  • Some patient variables that affect test results

Age Genetic variation

Gender Nutrition status

Diet Diagnostic and therapeutic Drugs procedures(PR&endoscopy)

Exercise Obesity

Posture Biorythm

Haemolysis,lipemia Special habits

& icterus

test collection
Test Collection
  • Timing of Collection
    • Therapeutic Drug Monitoring
      • Peak and trough collection times
    • Basal State Collections
      • Fasting requirements—no food or liquid except water(10-12h)
      • 2h postprandial, from the start of food .
    • Specimens affected by time of day, for example, cortisol, iron and TSH.
phlebotomy
Phlebotomy
  • Phlebotomy is a highly complex skill requiring expert knowledge, and critical judgment
  • venipuncture is a frequent medical procedure.
  • Phlebotomy errors may cause harm to patients or result in needle stick injury to the phlebotomist
error prevention
Error Prevention
  • Phlebotomy Education
    • Phlebotomists should have completed a standard academic course in phlebotomy and undergo thorough on-the-job training under the supervision of a senior phlebotomist
  • Continuing Education
    • Phlebotomists should participate in regular educational competency assessments (written and observational)
    • Professional Licensure
  • Phlebotomy Staffing
    • Adequate staffing to maintain collection standards
  • Technology
    • Use of barcode scanners for patient identification
slide18

1-posture:

The patient should be comfortably seated or supine for 20 minutes before sampling.Not standing

The patient arm should be extended in a straight line from the shoulder to the wrist.

2-collection site.

The median cubital vein is the preferred site.

Veins on the hand or at ankle may be used.

Avoid the arm with:

Extensive scarring or hematoma .,infection , edema ,burn ,

Containing I.V. access for I.V. infusion.

On the side of mastectomy.

phlebotomy technique
Phlebotomy Technique
  • Correct collection system
    • Evacuated tube system (Vacutainer) for large veins in antecubital fossa
    • Syringe for small, fragile veins or veins outside antecubital fossa
  • Venous access
    • Needle entry should be at 15 to 30 degrees depending on depth of vein
    • Needle entry should be in same direction as vein, centered over vein
    • Anchor vein to prevent movement during needle entry and to reduce pain to patient
phlebotomy technique errors
Phlebotomy Technique Errors
  • Tourniquet Application
    • Tourniquet tied too close to the venipuncture site can cause hematoma
    • Veins may not become prominent if tourniquet is tied too high (more than 3 to 4 inches above venipuncture site)
    • Tourniquet left on longer than one minute can result in hemoconcentration, affecting some test results
      • Tourniquet should be released as soon as needle is in the lumen of the vein and blood flow established
phlebotomy technique1
Phlebotomy Technique
  • Cleansing of venipuncture site
    • Thorough cleaning with alcohol
    • Allow alcohol to dry completely to avoid stinging sensation upon needle entry and hemolysis of sample
    • Samples such as blood cultures should be collected using iodine to cleanse site to ensure sterility of sample
      • Recollection rate for blood cultures ranges due to contamination is as high as 50% in hospitals with increased costs, patient overtreatment
test collection1
Test Collection
  • Additive : EDTA,citrat, lithium heparin ,oxalate,flourid
  • Hemolysis
    • Blood collected insufficient to amount of additive in tube,
    • Traumatic venipuncture
    • Blood collected from area with hematoma
    • Vigorous shaking of tubes after collection
    • Milking the site when collecting capillary samples and blood collected using a small diameter needle.
test collection2
Test Collection
  • Capillary Collections—finger stick or heel stick
    • Appropriate site
      • Heel stick—sides of the bottom surface of the heel
      • Finger stick—third or fourth fingers, perpendicular to fingerprint lines on fleshy pads on finger surface
    • Warming—Warm before collection to increase capillary blood flow near skin surface
    • Cleaning—cleanse site with alcohol and allow to air dry
    • Discard first drop of blood.
slide25
Recommended order of draw (NCCLS):
  • Blood Culture Bottles (Aerobic-Anaerobic)
  • Coagulation Tube
  • Serum Tube with or without clot activator, with or without gel separator
  • Heparin Tube with or without gel plasma separator
  • EDTA
  • Glycolytic Inhibitor
slide26
Correct Specimen Volume: All blood collection tubes need to be filled to the correct volume. This will ensure the proper amount of blood for the amount of additive in the tube (blood to additive ratio). For example, if a 5 mL draw heparin tubeis only filled with 3 mL of blood, the heparin concentration is erroneously high and may potentially interfere with some chemistry analytes, tube for Coagulation Studies incomplete filling results in specimen dilution and erroneous Prothrombin and aPTT test results.
slide27
Proper Tube Mixing:All tubes with additives need to be inverted to mix the additive evenly with the blood. Impropermixing of the tube after venipuncture could contribute to sample clotting.
e specimen transport
E) Specimen transport

Temperature

Light

transport errors
Transport Errors
  • Temperature
    • Specimens must be transported at the appropriate temperature for the required test
      • On ice—ABGs, Ammonia
      • Warmed -- (37 C), cryoglobulins
      • Avoid temperature extremes if transported via vehicle from other collection site
  • Transport Container
    • Some samples need to be protected from light, for example, bilirubin
    • Transport in leak-proof plastic bags in lockable rigid containers ,avoid agitation.
blood specimen transport
Blood Specimen Transport
  • Transport of blood specimens in the proper manner after collection ensures the quality of the sample
  • Timing
    • Some specimens must be transported immediatelyafter collection, for example Arterial Blood Gases.
    • Specimens for serum or plasma chemistry testing should be centrifuged and separated within two hours
slide31
Special Handling of Blood Specimens:Certain chemistry analytes will require the tube of blood to be chilled after collection in order to maintain the stability of the analyte. A slurry of ice and water is recommended for chilling the tubes of blood. Examples : adrenocorticotropic hormone (ACTH), angiotensin converting enzyme (ACE), acetone, ammonia, catecholamines, free fatty acids, lactic acid, pyruvate and renin ,PTH
blood gases analysis
Blood gases analysis

“Collection of a blood specimen, as well as its handling and transport, are key factors in the accuracy of clinical laboratory analysis and ultimately in delivering quality patient care”

”Arterial blood is one of the most sensitive of the specimens sent to the clinical laboratory for analysis”

”Blood gas and pH analysis has more immediacy on patient care than any other laboratory determination”

”In blood gas and pH analysis an incorrect result can often be worse for the patient than no result at all”

what is so special about blood gases
What is so special about blood gases?
  • NOT like other blood samples
  • STAT parameters
    • Short Turn Around Time
    • Must be analyzed within a short time
    • pO2, pCO2, pH, LAC, GLU
  • Valuable results right now
    • Not in one hour
  • Sample composition changes
  • Patient status changes
some points to keep in mind sampling from a lines
Some points to keep in mind - sampling from A-lines

Preparation prior to sampling

  • Label the sampler with patient ID
  • Use dry electrolyte balanced heparin
  • Endeavor to keep the patient’s respiratory condition stable for a certain period prior to sampling
  • Make sure that the a-line has been adequately cleared of flush solution
  • Aspirate the sample slowly to prevent degassing and hemolysis
  • Expel any air bubbles immediately after sampling
  • Mix the sample thoroughly with heparin after sampling

Sampling/handling

slide35

Analyze sample immediately

  • If storage is unavoidable, store the sample at room temperature for max. 30 min. Samples with expected high pO2 values should be analyzed within 5 min.

Storage/transport

  • Before transferring the sample into the analyzer mix thoroughly
  • Visually inspect the sample for clots and air bubbles
  • Enter patient ID in analyzer logs

Preparation prior to

sample transfer

slide36

Stabilization of the respiratory condition

  • To get a true picture of the patient’s respiratory condition the patient should ideally be in a steady state of ventilation
    • Patients should be at rest for 5 min
    • Ventilatory settings should be unchanged for 20 min
  • Pain and anxiety from arterial puncture may influence the steady state of respiration and should thus be minimized
storage recommendations
Storage recommendations

General storage recommendation

Do not cool the sample

Analyze within 30 minutes

For samples with high pO2

Analyze within 5 minutes

For special studies, e.g. shunt

Analyze within 5 minutes

For samples with high leukocyte or platelet count

Analyze within 5 minutes

Expected delayed analysis

When analysis is expected to be delayed for more than 30 minutes, the use of glass syringes and storage in ice slurry is recommended

  • Storage and transport time should be kept at a minimum
    • Volatile nature of gases
    • Continued metabolism in blood
  • For parameter panels including GLU/LAC, be aware that 30 minutes storage might lead to biased results
  • It is recommended by the NCCLS to avoid cooling of samples when kept in plastic
continued cellular metabolism in sample
Continued cellular metabolism in sample

pO2 since oxygen will still be consumed

pCO2 since carbon dioxide will still be produced

pH primarily due to the change in pCO2 and glycolysis

cCa2+ since the change in pH will influence the binding of Ca2+ to protein

cGlu since glucose will be metabolized

cLac due to glycolysis

slowing down the metabolism
Slowing down the metabolism

pO2

  • Blood gas samples in glass samplers can be cooled
  • Storing the sample at a lower temperature (0-4 °C) will slow down the metabolism by at least a factor of 10 [NCCLS]
  • Cool samples in an ice slurry or other suitable coolant
  • Never store the samples directly on ice as this causes hemolysis of the blood cells

Time

0-4 C

25 C

NCCLS Document C27-A; Blood Gas Pre-Analytical Considerations: Specimen Collection, Calibrations and Controls; Approved Guideline

potential preanalytical errors
Potential preanalytical errors

Preparation prior to sampling

  • Missing or wrong patient/sample identification
  • Use of the wrong type or amount of anticoagulant
    • - dilution due to the use of liquid heparin
    • - insufficient amount of heparin
    • - binding of electrolytes to heparin
  • Inadequate stabilization of the respiratory condition of the patient
  • Inadequate removal of flush solution in a-lines prior to blood collection
slide41

Sampling /handling

  • Mixture of venous and arterial blood during puncturing
  • Air bubbles in the sample
  • Insufficient mixing with heparin
  • Incorrect storage
  • Hemolysis of blood cells

Storage and transport

  • Visually inspect the sample for clots
  • Inadequate mixing of sample before analysis
  • Failure to identify the sample upon analysis

Prep prior to transfer

mixture of venous and arterial blood
Mixture of venous and arterial blood
  • When puncturing an artery it is important not accidentally to get the arterial blood mixed with venous blood
  • This may, for instance, occur, if you hit a vein before locating the artery
  • Even an admixture of a small amount of venous blood may significantly bias the results
  • This is especially true of pO2 and sO2, but other parameters may also be affected

Vein

Artery

40 mmHg / 5.3 kPa

100 mmHg / 13.3 kPa

mixture of venous and arterial blood1
Mixture of venous and arterial blood
  • In arteries the blood pressure is high enough to fill a self-filling syringe
  • If a self-filling syringe does not fill it may be because a vein has been hit
  • In that case a new sample should be taken

Vein:

Pressure rarely> 10 mmHg

Artery:

Systolic bloodpressure normally> 100 mmHg

inadequate removal of flush solution
Inadequate removal of flush solution
  • Flush solutions used in a-lines must be removed completely from the system to avoid a dilution of the blood sample
  • It is recommended to withdraw a volume equal to three to six times the “dead space” of the catheter system (NCCLS)
inadequate removal of flush solutions
Inadequate removal of flush solutions
  • Sample B and A are both a-line samples taken from the same patient immediately after each other
  • Before taking sample B only 1 mL of saline solution was removed - the tubing, however, looked red
  • Before taking sample A saline solution was removed as recommended

Sample A

ctHb 6.2 mmol/L

cGlu 9.6 mmol/L

cK+ 3.8 mmol/L

cNa+ 130 mmol/L

cCa2+ 1.00 mmol/L

cCl- 101 mmol/L

pH 7.271

pCO2 50.5 mmHg / 6.7 kPa

pO2 116.7 mmHg / 15.56 kPa

Sample B

ctHb 4.6 mmol/L

cGlu 6.9 mmol/L

cK+ 2.5 mmol/L

cNa+ 137 mmol/L

cCa2+ 0.61 mmol/L

cCl- 113 mmol/L

pH 7.275

pCO2 35.9 mmHg / 4.8 kPa

pO2 129.3 mmHg / 17.2 kPa

air bubbles
Air bubbles
  • Any air bubbles in the sample must be expelled as soon as possible after the sample has been drawn
    • before mixing the sample with heparin
    • before any cooling of the sample
  • Even small air bubbles may seriously affect the pO2 value of the sample, normally resulting in increased values
  • An air bubble whose relative volume is 0.5 to 1.0 % of the blood in the syringe is a potential source of a significant error
effect of air bubbles an example
Effect of air bubbles - an example
  • Sample A and B were taken from the same patient immediately after each other
  • Sample A without air bubbles was analyzed immediately after collection
  • 100 µL air was added to sample B (1 mL). It was stored cold (0-4 °C) for 30 minutes and mixed for 3 minutes before sample analysis

Sample A

pO2 288.6 mmHg / 38.5 kPa

(FIO2 1.000)

Sample B

pO2 253.3 mmHg / 33.8 kPa

(FIO2 1.000)

insufficient mixing with heparin
Insufficient mixing with heparin
  • Insufficient mixing can cause coagulation of the sample
  • It is recommended to mix the blood sample thoroughly with heparin
  • Invert the syringe 10 times and roll it between your palms
inadequate mixing an example
Inadequate mixing - an example
  • Sample A and B were taken from the same patient immediately after each other and stored cold for 10 minutes
  • Sample A was mixed in a rotator (14 revolutions/min) for 3 minutes
  • Sample B was mixed in a rotator (14 revolutions/min) for 1 minute

Sample A

ctHb 6.2 mmol/L

Sample B

ctHb 4.5 mmol/L

hemolysis of blood cells
The blood cells are relatively fragile, and therefore hemolysis may easily occur during blood sampling

Hemolysis may, for instance, occur due to

high filling pressure through a narrow entrance (e.g. during too vigorous sample aspiration, sample transfer to the analyzer, etc.)

vigorous rubbing or squeezing of the skin during capillary sampling

too vigorous mixing of the sample

cooling down the sample below 0 °C

Hemolysis of blood cells
the weak link
“The weak link”
  • Blood gas analyzers of today are highly accurate
  • Make sure that sample represents patient status
  • The preanalytical phase is the weak link in the Patient Focus Circle
  • Many potential errors
  • Can be overcome by
    • Training
    • User guidelines
    • Sampling products
specimen quality markers for rejection
Specimen Quality Markers for Rejection
  • Clotted
  • Hemolyzed
  • Underfilled, overfilled
  • Insufficient quantity
  • Incorrect labeling
  • Unlabeled specimen
  • Incorrect patient
  • Incorrect specimen
  • Contaminated
  • Lost sample
  • Too old to process
  • Broken and leaking
slide53
Finally…
  • The human role in sample collection makescomplete eliminationof errors associated with laboratory testing unrealistic
  • However, good practicesand compliance with the new strategiesforerrorpreventioncan lead to a substantial reductionin pre-analytical errors.