Pre-analytical Laboratory Errors

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• Role of clinician in lab result accuracy

Prof/Azza abd al baky
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Introduction

• Three phases of laboratory testing
  pre-analytical, analytical and post-analytical
• Pre-analyticalspecimen collection, transport and
  processing
• Analyticaltesting
• Post-analyticaltesting results transmission,
  interpretation, follow-up, retesting.

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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.

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The steps of the preanalytical phase

• Preparation prior to
• sampling

Sampling/handling
Storage/transport
Preparation prior to analysis
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Implications of errors

• and compromise the diagnosis and treatment of the
  patient

• may influence the quality of the final measured
  results ...

• Errors made in the period prior to the analysis
  of the sample ...

No result is better than bad result
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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

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Effects of Pre-analytical Variables on the
Quality of Laboratory Testing

• Paying close attention to the preanalytical
  variables associated with blood collection is
  critical in ensuring accurate test results in all
  areas of the clinical laboratory.

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The Pre-Analytical process

• Patient Identification
• Sampling Technique
• Test Collection Procedures
• Specimen Transport
• Specimen Processing

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The Pre-Analytical process

• Collect Sample
• Locate Patient
• Prep Patient
• Draw Sample
• Label
• Dispose of supplies

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Patient identification

• When identifying the patient, have them provide
  their full name, address, identification number
  and/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.

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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
  patients sample with a different patients label
  can certainly contribute to laboratory error.
  (Mislabeling ???)

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Factor affecting lab result

• Some patient variables that affect test results
• Age Genetic
  variation
• Gender Nutrition
  status
• Diet Diagnostic
  and therapeutic
  Drugs
  procedures(PRendoscopy)
• Exercise Obesity
• Posture Biorythm
• Haemolysis,lipemia Special habits
• icterus

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Test Collection

• Timing of Collection
• Therapeutic Drug Monitoring
• Peak and trough collection times
• Basal State Collections
• Fasting requirementsno 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.

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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

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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

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• 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.

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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

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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

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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

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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.

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Test Collection

• Capillary Collectionsfinger stick or heel stick
• Appropriate site
• Heel sticksides of the bottom surface of the
  heel
• Finger stickthird or fourth fingers,
  perpendicular to fingerprint lines on fleshy pads
  on finger surface
• WarmingWarm before collection to increase
  capillary blood flow near skin surface
• Cleaningcleanse site with alcohol and allow to
  air dry
• Discard first drop of blood.

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• 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

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• 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 tube is 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.

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• Proper Tube Mixing All tubes with additives need
  to be inverted to mix the additive evenly with
  the blood. Improper mixing of the tube after
  venipuncture could contribute to sample clotting.

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E) Specimen transport

• Temperature
• Light

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Transport Errors

• Temperature
• Specimens must be transported at the appropriate
  temperature for the required test
• On iceABGs, 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.

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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 immediately
  after collection, for example Arterial Blood
  Gases.
• Specimens for serum or plasma chemistry testing
  should be centrifuged and separated within two
  hours

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• 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

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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
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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

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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 patients 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
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• 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
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Stabilization of the respiratory condition

• To get a true picture of the patients
  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

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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

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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

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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
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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

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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
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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
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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 rarelygt 10 mmHg
Artery Systolic bloodpressure normallygt 100
mmHg
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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)

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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
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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

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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)
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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

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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
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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

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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

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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

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• Finally
• The human role in sample collection makes
  complete elimination of errors associated with
  laboratory testing unrealistic
• However, good practices and compliance with the
  new strategies for error prevention can lead to a
  substantial reduction in pre-analytical errors.

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