Preanalytical factors

Affecting clinical laboratory test result

BY

Assis.Prof Ayman Tallat Abbas, PhD

•Data and Lab

Management

•Safety

•Customer

Service

Patient/Client Prep

Sample Collection

Sample Receipt

and Accessioning

Sample TransportQuality Control

Record Keeping

ReportingPersonnel Competency

Test Evaluations

Testing

Types of clinical specimens

1- Blood2- Urine3- stool4- semen5- Peritoneal fluid6- Ascetic 7- CSF8- BM9- Tissue and organs

Types of Blood specimen

1- serumCentrifuge clotted blood

The upper part called serumNot contain fibrinogen

Chemistry studySerology study

Types of blood specimen

1- Whole bloodAnticoagulant tube

Cells + plasma

Hematolgy

Types of blood specimen

1- PlasmaCentrifuge whole blood

Upper layer called plasmaContain fibrinogen

Coagulation studies

Information required on laboratory requisition

Patient nameidentification number

Age Sex

Location/Tel.Nophysician

DiagnosisAntibiotic therapy

Collection date/time

Sites of blood collection

Vein punctureMost frequently used

For all blood chemistry

Arterial bloodBlood gasDangerous

Capillary bloodInfants, old patient

Small amount

Blood collection equipment

Needles Needle disposable syringe Collection tubes

ButterflyLancet microcontainrs

Torniquet

Adehesive stripGloves

Sterile cottonAlcohol , Iodine

Anticoagulants

Sodium citrate

Inhibit ionized calcium for ESR, Prothrobin time

Ethylene diamine tetra acetic acid “EDTA” disodium salt

Form calcium salt insoluble for hematology studies

Li - HeparinAntiprothrombin andthrompin for chemistery

Sodium fluridPrecipitate calcium in form of calcium floride and inhibit glycolysis for glucose

Cephalic Median cubital

Basilic

Antecubital fossa

1-Venous access difficulties use alternative sites

3- Excessive fist clenching elevate (K)

Veinpuncture

Locate the vein

Clean the puncture site

Guide needle toward the vein

Insert needle into the vein .

Aspirate the blood .

Remove the tourniquet .

Place a sterile pad over the

site and withdraw the needle

Have the patient extend the arm

and maintain light pressure on the site

Clean the puncture site

Puncture the finger

The blood must not be

squeezed out since this dilutes it

with fluid from the tissues, thus

altering the ratio of cellular elements to fluid, as well as the

ratio of cellular elements to

each other .

the alcohol or other antiseptic used can

coagulate the blood proteins causing

cell clumping and erroneous values as well as dilute cell volumes. This will result

in incorrect counts and differentials .

CAPILLARY PUNCTURE

Wipe away first drop of blood

Apply pressure to the site

Finger punctures should be

made along the lateral aspect of

the fingertip.

More nerve endings are located

on the fingerprint area of the

fingers; therefore, more pain

results from punctures in this

area.

.

Heel capillary puncture in infants

Milking or scraping the puncture site should be avoided since it can cause hemolysis or contamination of the specimen.

jugular vein of supine infant

External jugular venipuncture.

A syringe or a butterfly needle may be

used. Venous distention is aided when

an assistant's finger occludes the vein, or

when the infant cries.

The neck is extended, either over the

side of the bed or by placing a rolled

towel under the shoulders.

This procedure requires two persons. Gloves should be worn

In adults with adequate blood pressure, the syringe will “fill itself”; in hypotensive patients or children, the sample will need to be aspirated.Remove needle, apply pressure for 5 mins. or until bleeding is controlled.

Femoral artery:

Brachial artery

Radial or unlar

arterial puncture:

Specimen Disposal

Complication in blood collection

1-Failure to draw blood

2- Fainting

3- Hematoma

4- Edema

5- Obesity

6- I/V therapy

7- Hemoconcentration

8- Rolling vein

9- Collapse Veins

10- Hemolysis

Hemolysis

1.Forcing the blood through needle

2.Shaking the tube or bulb too vigorously after blood collection

3.Presence of excess of anticoagulant in the container

4.Centrifuging blood samples at high speed before completion of clotting

5.Freezing or thawing of blood

6.Using unclean tubes with residual detergent

7.Presence of water in the container

Chemical tests affected by hemolysis

•Using too small a needle

Serum potassium

Serum inorganic phosphorus

Serum Glutamate Oxaloacetate Transaminase(SGOT )

Serum Lactate Dehydrogenase (SLDH )

Serum acid phosphatase

Hemoglobin interferes in photometry

Specimen Rejection Criteria:

1.Unlabeled specimen

2. Insufficient patient information

3- Hemolyzed specimen

4. Wrong tube drawn

5. Lipemic

6. Inadequate volume for the amount of preservative

7. Insufficient quantity

8. Prolonged transport

Impact of Specimen Management on Patient Care

-Essential to accurate laboratory diagnosis

-Directly affects patient care and patient outcome

-Influences therapeutic decisions

-Impacts patient length of stay, hospital costs, and laboratory costs

-Influences laboratory efficiency

Pitfalls

*Saying “yes” to everything

Accepting every specimen

to physicians”No“Afraid to say

√ Someone with sufficient authority MUST

support laboratory policy

√ Good lab practice – Patients first!

√ Having no boundaries for technical issues

Pitfalls Lead to Errors Resulting

Delays in getting test results

Unnecessary re-draws/re-tests

Decreased customer satisfaction

Increased costs

Incorrect diagnosis / treatment

Injury

Death

Preanalytical factors

1- Patient complications

2- test collection error

3- specimen processing

4- specimen transportation

Patient complication

1- Diet

2- Exercise

3- Medication

4- Disease state

5- Body position

6- Lipemia

7- Icterus

Patient complication

Diet

* Metabolic products of food--- -- in venous blood

* Glucose, lipids and catecholamine

* Caffeine catecholamine

* Fasting specimen for accurate result

* Chemistry studies should be fasting 12 hour for accurate result

Exercise

Difference can accrue be observed in blood chemistry after heavy exercise

e.g proteinuria, LD isoenzymes, and elevations in creatine kinas (CK), CK-MB, and testosterone

medication

* Hepatotoxic drugs liver enzymes

* medication affecting plasma volume

Protein, CBC, BUN, iron and calcium

Age & Disease state

1- geriatric, oncology, hematological patients

2- pediatric patients have small vain traumatic collection

collapsed veins vessel wall injury hemolysis

Fragile veins

Patient age , sex and ethnicity

Obese patients difficult palpateAvoid probing with needle

useDorsal part of hand or wrist

Patient anxiety and stress

Affect analytical results

Albumin, insulin, glucose lactate, cholesterol

Body position

Changing from supin position to setting or satnding

costriuction B.V

Changing from sitting to supine shifting water+electrolyte into tissue causing hemoconcentratin affect CBC, protein,calcium,BUN,and lipids

Lipemia•● Displasment plasma volume

•and short sampling● Interfere with spectrophotometric,

turbidic measyrments

1- Fasting2- ultracenterfugation3- enzymatic

IcterusInterfering with several

Colorimetric assay

1-appropriate blankingmethod2-dual wavelenth method

Collection Errors

1- Pateint identification

2- Tourniquet and draw technique

3- draw volume

4- Mixing

Patient identification error

1- incorrect or missing

identification

2- Spicemen tube unlabeled (not

fixed will)

3- collection tube with wrong

patientnot label at time

of collection

labeled someone other thanphlebotomist who collect specimen

Tourniquet and draw technique

Single use and latex-freeTourniquet preferred

Placed 3 to 4 inches above venipuncture site*Too high veins not prominent* Too close hematoma

if longer minute only 1 hemoconcentration ( K, Prot,PCV)

near site of infusionBlood collection Cause

contamination / dilution

Traumatic drawfrom vessel wall injury can elevate

CK, myoglobin, and K

Order of blood draw

1- blood culture collected first to prevent contamination

2- EDTA tube before serum tube elevate K

3- Heparin tube before serum affect clotting

Draw Volume

Under filling Specimen dilution Erroneous PT,PTT and RBC’S morphology

OverfillingInadequate anticoagulation, fibrin formation, microclots,platelet clumping and affect instrument maintenance

Liquid additives in blood collection tubes will add a dilution factor compared with dry additives

Important

K3EDTA causes a dilution of approximately 1% to 2% compared with dry EDTA additive tube

Decrease

WBCs, RBCs, platelets,Hct and hemoglobin

Insufficient mixing cause microclots

MIXING

Affect

platelets, Hct and hemoglobin and fibrin formation instrument probe, fluid path obstruction and instrument down time

Excessive mixing or vigorous inversions

Hemolysis

Serum should be clotted before centrifugation (30-60 min)

Serum clotting time

Inadequate

Problem for many instruments because of latent fibrin formation ( probe clogging) and error result

Prolonged contact time of serum or plasma with RBCs

Exchange of compounds

Serum should separated within 2 hours

Transport Errors

1- Timing

2- Temperature

3- Transport container

Timing

Some specimens must be transported

immediately after collection. Ex.

Arterial blood gas

Specimen must centrifuged and

separated within 2 hours

Excessive transport time to analysis

result in hemolysis

Temperature

Appropriate temperature ex. On ice as

ammonia ----- on 37Co as cryoglobulins

Chilling ( 2 to 8 Co) not recommended for

whole blood beyond 2 hours.

Chilling specimen required for catecolamin,

ammonia, lactic acid,PTH and gastrin

Transport Container

Blood collection tubes should be stored

And transport in vertical position

1- promote complete clot

2- reduce agitation

3- stopper contamination

4- reduce hemolysis

Transport Container

Some samples need to be protected

From light as bilirubin

Transport in leak proof plastic bags

Or cubs