2 مشروع إعتماد معمل الكمياء الإكلينيكيه – مستشفى الطوارئ
3 Role of clinician in lab result accuracy Prof/Azza abd al baky
4 IntroductionThree phases of laboratory testing: pre-analytical, analytical and post-analyticalPre-analytical—specimen collection, transport and processingAnalytical—testingPost-analytical—testing results transmission, interpretation, follow-up, retesting.
5 Pre-analytical errors Pre- and post-analytical errors are estimated to constitute 90% of errorsErrors at any stage of the collection, testing and reporting process can potentially lead to a serious patient misdiagnosisErrors during the collection process are not inevitable but can be prevented with a diligent application of quality control, continuing education and effective collection systems.
6 The steps of the preanalytical phase Preparation prior tosamplingSampling/handlingStorage/transportPreparation prior to analysis
7 Implications of errors Errors made in the period prior to the analysis of the sample ...may influence the quality of the final measured results ...and compromise the diagnosis and treatment of the patientNo result is better than bad result
8 Complex and labor intensive The more steps involved in a process, the more likely there will be errors committed% of all test errors occur in the preanalytical phaseStankovic 2008“Quality Improvements in the Preanalytical Phase:Focus on Urine Specimen Workflow”
9 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.
10 The Pre-Analytical process Patient IdentificationSampling TechniqueTest Collection ProceduresSpecimen TransportSpecimen Processing
11 The Pre-Analytical process Collect Sample:Locate PatientPrep PatientDraw SampleLabelDispose of supplies
12 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.
13 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 ???)
14 Factor affecting lab result Some patient variables that affect test resultsAge Genetic variationGender Nutrition statusDiet Diagnostic and therapeutic Drugs procedures(PR&endoscopy)Exercise ObesityPosture BiorythmHaemolysis,lipemia Special habits& icterus
15 Test Collection Timing of Collection Therapeutic Drug Monitoring Peak and trough collection timesBasal State CollectionsFasting 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.
16 PhlebotomyPhlebotomy is a highly complex skill requiring expert knowledge, and critical judgmentvenipuncture is a frequent medical procedure.Phlebotomy errors may cause harm to patients or result in needle stick injury to the phlebotomist
17 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 phlebotomistContinuing EducationPhlebotomists should participate in regular educational competency assessments (written and observational)Professional LicensurePhlebotomy StaffingAdequate staffing to maintain collection standardsTechnologyUse of barcode scanners for patient identification
18 1-posture: 2- collection site. The patient should be comfortably seated or supine for 20 minutes before sampling.Not standingThe 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.
19 Phlebotomy Technique Correct collection system Venous access Evacuated tube system (Vacutainer) for large veins in antecubital fossaSyringe for small, fragile veins or veins outside antecubital fossaVenous accessNeedle entry should be at 15 to 30 degrees depending on depth of veinNeedle entry should be in same direction as vein, centered over veinAnchor vein to prevent movement during needle entry and to reduce pain to patient
21 Phlebotomy Technique Errors Tourniquet ApplicationTourniquet tied too close to the venipuncture site can cause hematomaVeins 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 resultsTourniquet should be released as soon as needle is in the lumen of the vein and blood flow established
22 Phlebotomy Technique Cleansing of venipuncture site Thorough cleaning with alcoholAllow alcohol to dry completely to avoid stinging sensation upon needle entry and hemolysis of sampleSamples such as blood cultures should be collected using iodine to cleanse site to ensure sterility of sampleRecollection rate for blood cultures ranges due to contamination is as high as 50% in hospitals with increased costs, patient overtreatment
23 Test CollectionAdditive : EDTA,citrat, lithium heparin ,oxalate,flouridHemolysisBlood collected insufficient to amount of additive in tube,Traumatic venipunctureBlood collected from area with hematomaVigorous shaking of tubes after collectionMilking the site when collecting capillary samples and blood collected using a small diameter needle.
24 Test Collection Capillary Collections—finger stick or heel stick Appropriate siteHeel stick—sides of the bottom surface of the heelFinger stick—third or fourth fingers, perpendicular to fingerprint lines on fleshy pads on finger surfaceWarming—Warm before collection to increase capillary blood flow near skin surfaceCleaning—cleanse site with alcohol and allow to air dryDiscard first drop of blood.
25 Recommended order of draw (NCCLS): Blood Culture Bottles (Aerobic-Anaerobic)Coagulation TubeSerum Tube with or without clot activator, with or without gel separatorHeparin Tube with or without gel plasma separatorEDTAGlycolytic Inhibitor
26 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.
27 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.
29 Transport Errors Temperature Transport Container Specimens must be transported at the appropriate temperature for the required testOn ice—ABGs, AmmoniaWarmed -- (37 C), cryoglobulinsAvoid temperature extremes if transported via vehicle from other collection siteTransport ContainerSome samples need to be protected from light, for example, bilirubinTransport in leak-proof plastic bags in lockable rigid containers ,avoid agitation.
30 Blood Specimen Transport Transport of blood specimens in the proper manner after collection ensures the quality of the sampleTimingSome 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
31 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
32 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”
33 What is so special about blood gases? NOT like other blood samplesSTAT parametersShort Turn Around TimeMust be analyzed within a short timepO2, pCO2, pH, LAC, GLUValuable results right nowNot in one hourSample composition changesPatient status changes
34 Some points to keep in mind - sampling from A-lines Preparation prior to samplingLabel the sampler with patient IDUse dry electrolyte balanced heparinEndeavor to keep the patient’s respiratory condition stable for a certain period prior to samplingMake sure that the a-line has been adequately cleared of flush solutionAspirate the sample slowly to prevent degassing and hemolysisExpel any air bubbles immediately after samplingMix the sample thoroughly with heparin after samplingSampling/handling
35 Storage/transport 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/transportBefore transferring the sample into the analyzer mix thoroughlyVisually inspect the sample for clots and air bubblesEnter patient ID in analyzer logsPreparation prior tosample transfer
36 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 ventilationPatients should be at rest for 5 minVentilatory settings should be unchanged for 20 minPain and anxiety from arterial puncture may influence the steady state of respiration and should thus be minimized
37 Storage recommendations General storage recommendationDo not cool the sampleAnalyze within 30 minutesFor samples with high pO2Analyze within 5 minutesFor special studies, e.g. shuntFor samples with high leukocyte or platelet countExpected delayed analysisWhen analysis is expected to be delayed for more than 30 minutes, the use of glass syringes and storage in ice slurry is recommendedStorage and transport time should be kept at a minimumVolatile nature of gasesContinued metabolism in bloodFor parameter panels including GLU/LAC, be aware that 30 minutes storage might lead to biased resultsIt is recommended by the NCCLS to avoid cooling of samples when kept in plasticPlastic syringes are not impermeable to gas diffusion, and will allow exchange of oxygen and carbon dioxide with the ambient air.When the sample is cooled, the blood can dissolve more gas, I.e. a cooled, stored sample will potentially take up enough oxygen to bias the sample.
38 Continued cellular metabolism in sample pO2 since oxygen will still be consumedpCO2 since carbon dioxide will still be producedpH primarily due to the change in pCO2 and glycolysiscCa2+ since the change in pH will influence the binding of Ca2+ to proteincGlu since glucose will be metabolizedcLac due to glycolysisMetabolically active cells, such as leukocytes and thrombocytes, will continue to metabolize O2 to CO2The fall in pO2 is accelerated if the original sample pO2 is highHigh levels of leukocytes, such as found in leukemic patients, may cause a significant fall in pO2 in a short period of time
39 Slowing down the metabolism pO2Blood gas samples in glass samplers can be cooledStoring 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 coolantNever store the samples directly on ice as this causes hemolysis of the blood cellsTime0-4 C25 CNCCLS Document C27-A; Blood Gas Pre-Analytical Considerations: Specimen Collection, Calibrations and Controls; Approved Guideline
40 Potential preanalytical errors Preparation prior to samplingMissing or wrong patient/sample identificationUse of the wrong type or amount of anticoagulant- dilution due to the use of liquid heparin- insufficient amount of heparin- binding of electrolytes to heparinInadequate stabilization of the respiratory condition of the patientInadequate removal of flush solution in a-lines prior to blood collection
41 Sampling /handlingMixture of venous and arterial blood during puncturingAir bubbles in the sampleInsufficient mixing with heparinIncorrect storageHemolysis of blood cellsStorage and transportVisually inspect the sample for clotsInadequate mixing of sample before analysisFailure to identify the sample upon analysisPrep prior to transfer
42 Mixture of venous and arterial blood When puncturing an artery it is important not accidentally to get the arterial blood mixed with venous bloodThis may, for instance, occur, if you hit a vein before locating the arteryEven an admixture of a small amount of venous blood may significantly bias the resultsThis is especially true of pO2 and sO2, but other parameters may also be affectedVeinArtery40 mmHg / 5.3 kPa100 mmHg / 13.3 kPa
43 Mixture of venous and arterial blood In arteries the blood pressure is high enough to fill a self-filling syringeIf a self-filling syringe does not fill it may be because a vein has been hitIn that case a new sample should be takenVein:Pressure rarely > 10 mmHgSelf-filling syringes typically fill upon a pressure of 20 mmHgArtery:Systolic blood pressure normally > 100 mmHg
44 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 sampleIt is recommended to withdraw a volume equal to three to six times the “dead space” of the catheter system (NCCLS)
45 Inadequate removal of flush solutions Sample B and A are both a-line samples taken from the same patient immediately after each otherBefore taking sample B only 1 mL of saline solution was removed - the tubing, however, looked redBefore taking sample A saline solution was removed as recommendedSample ActHb 6.2 mmol/LcGlu 9.6 mmol/LcK+ 3.8 mmol/LcNa+ 130 mmol/LcCa mmol/LcCl- 101 mmol/LpH 7.271pCO mmHg / 6.7 kPapO mmHg / kPaSample BctHb 4.6 mmol/LcGlu 6.9 mmol/LcK+ 2.5 mmol/LcNa+ 137 mmol/LcCa mmol/LcCl- 113 mmol/LpH 7.275pCO mmHg / 4.8 kPapO mmHg / 17.2 kPaSaline solution is kept in a plastic bag which is permeable to air. Oxygen and carbon dioxide equilibrates with the ambient air and thus represents high tensions.
46 Air bubblesAny air bubbles in the sample must be expelled as soon as possible after the sample has been drawnbefore mixing the sample with heparinbefore any cooling of the sampleEven small air bubbles may seriously affect the pO2 value of the sample, normally resulting in increased valuesAn 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
47 Effect of air bubbles - an example Sample A and B were taken from the same patient immediately after each otherSample A without air bubbles was analyzed immediately after collection100 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 analysisSample ApO mmHg / 38.5 kPa(FIO )Sample BpO mmHg / 33.8 kPa(FIO )
48 Insufficient mixing with heparin Insufficient mixing can cause coagulation of the sampleIt is recommended to mix the blood sample thoroughly with heparinInvert the syringe 10 times and roll it between your palmsRed blood cells tend to stack (like coins or plates) due to their concave shape. Stacking is prevented by mixing in two dimensions.
49 Inadequate mixing - an example Sample A and B were taken from the same patient immediately after each other and stored cold for 10 minutesSample A was mixed in a rotator (14 revolutions/min) for 3 minutesSample B was mixed in a rotator (14 revolutions/min) for 1 minuteSample ActHb 6.2 mmol/LSample BctHb 4.5 mmol/L
50 Hemolysis of blood cells The blood cells are relatively fragile, and therefore hemolysis may easily occur during blood samplingHemolysis may, for instance, occur due tohigh 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 samplingtoo vigorous mixing of the samplecooling down the sample below 0 °C
51 “The weak link” Blood gas analyzers of today are highly accurate Make sure that sample represents patient statusThe preanalytical phase is the weak link in the Patient Focus CircleMany potential errorsCan be overcome byTrainingUser guidelinesSampling productsBG Analyzers of today are highly accurate.The results reflect the composition of the sample – i.e. make sure that the sample represents the patient!Studies have shown that up to 60% of all errors in blood sampling are related to the preanalytical phase.Conclusion: need for training and samplers that are easy to use and do not introduce errors.
52 Specimen Quality Markers for Rejection ClottedHemolyzedUnderfilled, overfilledInsufficient quantityIncorrect labelingUnlabeled specimenIncorrect patientIncorrect specimenContaminatedLost sampleToo old to processBroken and leaking
53 Finally…The human role in sample collection makes complete elimination of errors associated with laboratory testing unrealisticHowever, 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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