Preanalytical error clinical chemical tests

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.

3 Prof Asmaa El Reweny, MD

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


“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”


9

Sources of Lab Errors

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.


Steps of Pre-Analytical process

Patient Identification

Sampling Technique Outside Lab

Collection Procedures

Specimen Transport

Specimen Processing Inside Lab


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


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)


Change (%) of serum concentration of different

analytes after a standard meal

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


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 ???)


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


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.


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.


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.


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.


Increase (%) of plasma concentration of various analytes

when changing from supine to an upright position


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.


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 ).



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.



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.


Change (%) in serum concentration of various analytes after tourniquet

application time of 6 min

Collection

Additives used:

- EDTA,

- Citrate,

- Lithium heparin,

- Fluoride/ Oxalate


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.


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.


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.


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


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.


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.


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.


Sufficient mixing with heparin

Insufficient mixing can

cause coagulation of the

sample

Invert the syringe 10 times

and roll it between your

palms


Transportation to the Laboratory

Specimen Transport

- Time

- Temperature

- Light


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.


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.


Transportation - Common problems


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…


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


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


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.

Changes in various analytes with increasing hemolysis

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


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


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

Prof Asmaa Elreweny, MD 59

الحمد هلل رب العالمين

هي بلدة شهدت مواطن التنزيل مشى في طرق اتها ميكائيل وجبرائيل

60 Prof Dr Asmaa El-Reweny