Preanalytical Errors in Medical Laboratory Meeqat General Hospital, 25 October 2016 By Prof. Asmaa El Reweny, MD Professor & Consultant of Clinical & Chemical Pathology, Faculty of Medicine, Cairo University & AMS, Taibah University (2006-2016)
Preanalytical Errors
in Medical Laboratory Meeqat General Hospital, 25 October 2016
By
Prof. Asmaa El Reweny, MD
Professor & Consultant of Clinical & Chemical
Pathology, Faculty of Medicine, Cairo University &
AMS, Taibah University (2006-2016)
Objectives At the end of this lecture you will be able to:
1- Identify what is meant by preanalytical
period.
2- Recognize magnitude of preanalytical
errors in relation to total analytical errors.
3- Identify steps of preanalytical process & its
potential errors.
4- Recognize how to avoid these errors
5- Identify markers for sample rejection 2 Prof Asmaa El Reweny, MD
Introduction Three phases of laboratory testing:
Pre-analytical:
Specimen collection, transport & processing
Analytical:
Testing
Post-analytical:
Results transmission, interpretation, follow-
up, retesting.
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Why Preanalytics?
Preanalytical variables can dramatically
affect the results of laboratory tests.
Paying close attention to control the
preanalytical variables will help to ensure
accurate test results in clinical laboratory.
Implications of Errors
Compromise
diagnosis &
treatment of
the patient
• May influence
the quality of
final results ...
• Errors made
in the period
prior to the
analysis ... No result is better than bad result.
Accurate result is the best of all. 5 Prof Asmaa El Reweny, MD
Steps of preanalytical phase
Preparation prior to
sampling
Sampling/handling
Transport/Storage
Preparation prior to analysis
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“The weak link”
The preanalytical phase
is the weak link in the
Patient Focus Circle.
The more steps
involved in a process,
the more likely there
will be errors.
Magnitude of Preanalytical Errors
In Relation To Total Analytical Errors
93% (2014)
32 - 75% *
*Stankovic 2008
“Quality Improvements in the Preanalytical Phase:
Focus on Urine Specimen Workflow”
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Error
Source
Ross and Boone1
Plebani et al.2
Pre-analytical
46%
68%
Analytical
7%
13%
Post-analytical
47%
19%
1 – Ross and Boone, Inst. of Critical Issues in Health Lab Practices, DuPont Press, 1991
2 - Plebani and Carraro. Clin Chem 43:1348, 1997
Total Analytical Error Distribution
Pre-analytical errors
Pre-& post-analytical errors: > 90% of errors
These potential errors are not inevitable but
could be prevented with a diligent application of quality control, continuing education and effective collection systems.
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Steps of Pre-Analytical process
Patient Identification
Sampling Technique Outside Lab
Collection Procedures
Specimen Transport
Specimen Processing Inside Lab
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Attention to the preanalytical variables
associated with blood collection is
critical in ensuring accurate test
results.
Record significant variables on request
form.
Effects of Pre-analytical Variables on
Quality of Laboratory Testing
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Effects of Pre-analytical Variables on
the Results of Laboratory Testing Some patient variables that affect test results
- Age - Genetic variation/ Race
- Sex - Nutritional status
- Diet - Diagnostic & therapeutic
- Drugs procedures (PR, endoscopy)
- Exercise - Pregnancy
- Posture - Timing: Biorythm
- Special habits - Hemolysis, lipemia, Jaundice
- Diagnosis (provisional)
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When identifying the patient, get:
Full name
Age & sex
Address/Nationality
Identification number:
Hospital No for inpatients,
Identification band should contain the above information (confirm before venipuncture).
Patient and specimen
identification
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Patient Identification: It is important to
identify a patient accurately so that blood is
collected & labeled from the correct person
with his correct data.
(otherwise mislabeling ???)
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Patient and specimen identification
The highest frequency of errors occurs with
the use of handwritten labels & request forms.
These can be eliminated by:
Confirming patient’s identifiers (name, medical
record number, date of birth, room location or
address)
Barcode technology.
Locate Patient
Prepare Patient
Draw Sample
Label
Dispose of supplies
Sampling and Collection
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Sample 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), (12-14 h for TG)
2h postprandial, from the start of food .
Specimens affected by time of day, for
example, cortisol, iron and TSH.
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Diurnal variation of selected analytes
Analytes
(serum, urine)
Maximum
(time of day)
Minimum
(time of day)
Amplitude
% of daily mean
Cortisol (S,U) 5-8 21-3 180-200
Prolactin 5-7 10-12 80-100
Aldosterone 2-4 12-14 60-80
Renin 0-6 10-12 120-140
Iron (S) 14-18 2-4 50-70
Phosphate (S) 2-4 8-12 30-40
Phosphate (U) 18-24 4-8 60-80
Timing of Collection
Between 7 and 9 a.m.
Before interfering diagnostic and therapeutic procedures
In drug monitoring: consideration of the peak after administration and the steady state phase before the next dose
Documentation of the exact time of sampling is very important !
Phlebotomy
Venipuncture requires expert knowledge
and critical judgment.
Phlebotomy errors may cause harm to
patients or result in needle stick injury to
the phlebotomist.
It could result in many preanalytical errors
in Lab results.
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Error Prevention
Phlebotomy Education Academic course and training under the supervision
of a senior phlebotomist.
Continuous Medical Education 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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Phlebotomy Technique
1. Posture:
- Comfortably seated patient or supine for 20 min
before sampling (not standing).
- The 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.
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Increase (%) of plasma concentration of various analytes
when changing from supine to an upright position
Phlebotomy Technique
Cleaning of venipuncture site
Thorough cleaning with alcohol
Allow alcohol to dry completely to avoid
stinging sensation and hemolysis of sample
Iodine for blood culture samples (sterile
sample)
NB: contamination occurs in 50% at some
hospitals with increased costs & patient
overtreatment.
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Collection site
Avoid the arm with: - Extensive scarring, hematoma, infection, edema
or burn
- On the same side of mastectomy.
- I.V. infusion (Document if IV ).
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Phlebotomy Technique
3. Correct collection system
Vacutainers for large veins in antecubital fossa.
Syringe for small, fragile veins or veins outside antecubital fossa.
4. Venous access Needle entry should be at 15-30o 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 venipuncture site
can cause hematoma.
Veins may not become prominent if tourniquet
is tied too high (> 3-4 inches above venipuncture site)
Tourniquet left for > 1 min can result in
hemoconcentration, affecting some test results.
Tourniquet should be released as soon as
needle is in the lumen of vein and blood flow is
established.
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Collection
Additives used:
- EDTA,
- Citrate,
- Lithium heparin,
- Fluoride/ Oxalate
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Selection of tubes - Common problems
Solution: New sample needs to be sent to lab.
Typical errors Consequences
Incorrect tube • cannot be analysed
• risk of contamination
Incorrect order of tubes • contaminations
• false results
Common problem: Hemolysis
Causes of Hemolysis
Traumatic venipuncture
Blood collected from area with hematoma
Vigorous shaking after collection
Milking the site when collecting capillary samples
Blood collected using a small diameter needle.
High filling pressure through a narrow entrance (e.g
during too vigorous sample aspiration)
Cooling down the sample < 0 °C.
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Hemolysis:
Affects analytes that are present at
higher concentrations in erythrocytes
than in plasma (K, LD, AST, Mg, P, ACP)
Hemolysis may also affect unblanked
analytical methods.
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Collection Capillary Collections:
Appropriate site
Heel stick: sides of bottom surface of the heel (infants)
Finger stick: third or fourth fingers, perpendicular to fingerprint lines on fleshy pads on finger surface.
Warm before collection to increase capillary blood flow near skin surface.
Clean site with alcohol and allow to dry.
Discard first drop of blood.
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Recommended order of draw (NCCLS):
1. Blood Culture Bottles
2. Coagulation Tube
3. Serum Tube with or without clot activator,
with or without gel separator
4. Heparin Tube with or without gel plasma
separator
5. EDTA
6. Glycolytic Inhibitor
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Correct Specimen Volume
(blood to additive ratio).
Little blood in heparin tube makes heparin
relatively higher in concentration and may
potentially interfere with some chemistry
analysis
In Coagulation Studies incomplete filling
results in specimen dilution and prolonged
Prothrombin Time & PTT results.
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Proper Tube Mixing:
All tubes with additives need to be inverted (10 times) to mix the additive evenly with the blood. Improper mixing of the tube after venipuncture could contribute to sample clotting.
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Sampling - Common problems
Typical errors Consequences Trauma, strangulation, stasis hemolysis, hemoconcentration
IV contamination dilution, false results
Sample volume is insufficient incomplete lab results, repeat
sampling
Incomplete filling of tubes inappropriate anticoagulant:blood
ratio, false results
Inappropriate mixing clotted, hemolysed sample
Solution:
Lab report with preanalytical comment (if problem
recognized).
New sample is requested.
Infusions/transfusions as interfering factor and/or
contaminants of laboratory tests
Infusion/
transfusion Analyte affected Trend Comments
Electrolytes K, Na, Mg contamination
Glucose glucose contamination
inorg. phosphate,
K
insulin
amylase,
bilirubin
up to 15%, particularly
in neonates
Dextran Thrombin time 5-10 sec slower
total protein Method- dependent
urea
Infusion, transfusion, catheters
Blood should never be collected proximal to the infusion site.
It is recommended that the laboratory be informed of when and what type of infusion were carried out and when blood samples were taken.
If samples are to be taken from catheters, the cannula should be rinsed with isotonic saline suitable for the volume of catheter. The first 5 ml of blood should be discarded before a blood sample is taken.
Some points in sampling from A-lines
Preparation prior
to sampling
Sampling/ handling
•Label with patient ID. •Use dry electrolyte balanced heparin. •Keep patient 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 & hemolysis. •Expel any air bubbles immediately after sampling. •Mix sample thoroughly with heparin after sampling.
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Sufficient mixing with heparin
Insufficient mixing can
cause coagulation of the
sample
Invert the syringe 10 times
and roll it between your
palms
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Blood Specimen Transport
Proper transport of specimens after collection ensures quality of sample
(& tests).
Timing
Some specimens must be transported
immediately (Arterial Blood Gases).
Specimens for serum or plasma chemistry testing should be centrifuged and separated within 2 hs.
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Transport Errors
Temperature On ice: ABGs, Ammonia
Warmed (37 C): cryoglobulins
Avoid temperature extremes if transported via vehicle.
Transport Container Some samples need to be protected from light
e.g. bilirubin.
Transport in leak-proof plastic bags in lockable rigid containers & avoid agitation.
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Transportation - Common problems
Typical errors Consequences
Delay False results
(high K)
Delay in reporting
Burden and harm to patient
sample stability deteriorates,
certain components break down
Inappropriate storage
Solution: New sample is requested.
Special Handling of Blood Specimens:
Chilled tube:
To maintain stability of some analytes, a slurry of ice & water is recommended for chilling.
Examples :
1. ACTH, PTH, Catecholamine & Renin
2. Angiotensin Converting Enzyme (ACE),
3. Acetone, Ammonia,, Free Fatty Acids, Lactic Acid, Pyruvate…
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Intra-laboratory Handling,
Preparation and Storage of Samples
Registration, identification
Checking for clots
Centrifugation
Distribution
Storage (non routine daily analysis ,
for post-analysis if it is needed)
Intra-laboratory handling –
Common problems
Typical errors Consequences
Native blood centrifugated before
clotting
Hemolysed sample, fibrin strand
in serum, clogging
Inappropriate melting of frozen
specimens
False concentration or
precipitation, …… false result
Inappropriate storage of samples
in lab (sample ID lost,
contamination, break down of
unstable components … etc.)
False results
Contamination
Clots in anticoagulated blood
Cryoglobulins
False results
Solution: New sample is requested when necessary.
Common Interferences
Typical errors Consequences
in vitro hemolysis •High K, LDH, HB
•interference with many analytical
procedures
Hyperlipidaemia •Pseudo-hyponatraemia
•Interference with many analytical
procedures
Hyperbilirubinaemia •Interferences
Drugs •Interference
Solution: - New sample is requested.
- Alternative methods used.
- Results commented.
Quality Markers for
Rejection of Samples
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 strategies for error prevention can lead to a substantial reduction in pre-analytical errors.
Thank You
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References
[ 1] Magee, L. S. Preanalytical variables in the chemistry
laboratory. Becton Dickinson Lab Notes 2005; 1 (1)
[2] Sarstedt AG: Tipps und Tricks in der Preanalytik, 2008
[3] Tyndall, L. Managing Preanalytical Variability in
Hematology. Becton Dickinson Lab Notes 2004; 14 (1)
[4] WHO guidelines on drawing blood: best practices in
phlebotomy, 2010
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