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5 preanalytical factors affecting clinical laboratory test result


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  • 1. Preanalytical factors Affecting clinicallaboratory test result BY Assis.Prof Ayman Tallat Abbas, PhD
  • 2. Patient/Client Prep Sample Collection Personnel Competency Reporting Test Evaluations •Data and Lab Management •Safety •Customer Service Sample Receipt and AccessioningRecord Keeping Quality Control Sample Transport Testing
  • 3. Types of clinical specimens1- Blood2- Urine3- stool4- semen5- Peritoneal fluid6- Ascetic7- CSF8- BM9- Tissue and organs
  • 4. Types of Blood specimen1- serum Centrifuge clotted blood The upper part called serum Not contain fibrinogen Chemistry study Serology study
  • 5. Types of blood specimen1- Whole blood Anticoagulant tube Cells + plasma Hematolgy
  • 6. Types of blood specimen1- Plasma Centrifuge whole blood Upper layer called plasma Contain fibrinogen Coagulation studies
  • 7. Information required onlaboratory requisition Patient name identification number Diagnosis Age Antibiotic therapy Sex Collection date/time Location/Tel.No physician
  • 8. Sites of blood collection Vein puncture Most frequently used Arterial bloodFor all blood chemistry Blood gas Dangerous Capillary blood Infants, old patient Small amount
  • 9. Blood collection equipment Needles Collection tubes Needle disposable syringe Butterfly microcontainrs Lancet Torniquet Sterile cotton Alcohol , IodineAdehesive strip Gloves
  • 10. Anticoagulants Sodium Inhibit ionized calcium for ESR, citrate Prothrobin time Ethylene diamine Form calcium salt insoluble for tetra acetic acid hematology studies “EDTA” disodium salt Antiprothrombin and Li - Heparin thrompin for chemistery Precipitate calcium in form of calciumSodium flurid floride and inhibit glycolysis for glucose
  • 11. Cephalic Median cubital Basilic Veinpuncture Antecubital fossa 1-Venous access difficulties use alternative sites 3- Excessive fist clenching elevate (K)
  • 12. Locate the vein Clean the puncture siteGuide needle toward the vein
  • 13. .Insert needle into the vein .Aspirate the blood .Remove the tourniquet
  • 14. Place a sterile pad over the site and withdraw the needle Have the patient extend the armand maintain light pressure on the site
  • 15. CAPILLARY PUNCTURE Clean the puncture sitethe alcohol or other antiseptic used cancoagulate the blood proteins causingcell clumping and erroneous values aswell as dilute cell volumes. This will incorrect counts and differentials 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
  • 16. Wipe away first drop of blood Apply pressure to the site
  • 17. Finger punctures should bemade along the lateral aspect ofthe fingertip.More nerve endings are locatedon the fingerprint area of thefingers; therefore, more painresults from punctures in thisarea.
  • 18. Heel capillary puncture in infantsMilking or scraping the puncturesite should be avoided since it cancause hemolysis or contamination.of the specimen
  • 19. jugular vein of supine infantExternal jugular venipuncture.A syringe or a butterfly needle may beused. Venous distention is aided whenan assistants finger occludes the vein, orwhen the infant cries. The neck is extended, either over theside of the bed or by placing a rolledtowel under the shoulders.This procedure requires two persons.Gloves should be worn
  • 20. arterial puncture: Radial or unlar 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.Brachial artery Femoral artery:
  • 21. Specimen Disposal
  • 22. Complication in blood collection1-Failure to draw blood 8- Rolling vein2- Fainting 9- Collapse Veins3- Hematoma 10- Hemolysis4- Edema5- Obesity6- I/V therapy7- Hemoconcentration
  • 23. Hemolysis1.Forcing the blood through needle2.Shaking the tube or bulb too vigorously afterblood collection3.Presence of excess of anticoagulant in thecontainer4.Centrifuging blood samples at high speed beforecompletion of clotting5.Freezing or thawing of blood6.Using unclean tubes with residual detergent7.Presence of water in the container
  • 24. Chemical tests affected by hemolysis Using too small a needle •Serum potassiumSerum inorganic phosphorusSerum Glutamate Oxaloacetate)Transaminase(SGOT)Serum Lactate Dehydrogenase (SLDHSerum acid phosphataseHemoglobin interferes in photometry
  • 25. Specimen Rejection Criteria:1.Unlabeled specimen2. Insufficient patient information3- Hemolyzed specimen4. Wrong tube drawn5. Lipemic6. Inadequate volume for the amount ofpreservative7. Insufficient quantity8. Prolonged transport
  • 26. Impact of Specimen Management on Patient Care-Essential to accurate laboratory diagnosis-Directly affects patient care and patientoutcome-Influences therapeutic decisions-Impacts patient length of stay, hospital costs,and laboratory costs-Influences laboratory efficiency
  • 27. Pitfalls*Saying “yes” to everythingAccepting every specimen Afraid to say “No” to physicians√ Someone with sufficient authority MUSTsupport laboratory policy√ Good lab practice – Patients first!√ Having no boundaries for technical issues
  • 28. Pitfalls Lead to Errors Resulting Delays in getting test resultsUnnecessary re-draws/re-testsDecreased customer satisfactionIncreased costsIncorrect diagnosis / treatmentInjuryDeath
  • 29. Preanalytical factors1- Patient complications2- test collection error3- specimen processing4- specimen transportation
  • 30. Patient complication1- Diet 5- Body position2- Exercise 6- Lipemia3- Medication 7- Icterus4- Disease state
  • 31. 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 foraccurate result
  • 32. ExerciseDifference can accrue beobserved in bloodchemistry after heavyexercisee.g proteinuria, LDisoenzymes, andelevations in creatinekinas (CK), CK-MB, andtestosterone
  • 33. medication* Hepatotoxic drugs liverenzymes* medication affecting plasmavolumeProtein, CBC, BUN, iron andcalcium
  • 34. Age & Disease state1- geriatric, oncology,hematological patients Fragile veins2- pediatric patients have small vain traumatic collectioncollapsed veins vessel wallinjury hemolysis
  • 35. Patient age , sex and ethnicity Affect analytical results Obese patients difficult palpate Avoid probing with needle use Dorsal part of hand or wrist Patient anxiety and stress Albumin, insulin, glucose lactate, cholesterol
  • 36. Body positionChanging from supin position to setting or satndingcostriuction B.VChanging from sitting tosupine shiftingwater+electrolyte intotissue causinghemoconcentratin affectCBC,protein,calcium,BUN,andlipids
  • 37. ● Displasment plasma volume•Lipemia and short sampling• ● Interfere with spectrophotometric, turbidic measyrments 1- Fasting 2- ultracenterfugation 3- enzymatic 1-appropriate blanking Interfering with severalIcterus Colorimetric assay method 2-dual wavelenth method
  • 38. Collection Errors1- Pateint 3- draw volumeidentification2- Tourniquet anddraw technique 4- Mixing
  • 39. Patient identification error 1- incorrect or missing identification 2- Spicemen tube unlabeled (not fixed will) 3- collection tube with wrong patient not label at time of collection labeled someone other than phlebotomist who collect specimen
  • 40. Tourniquet and draw techniqueSingle use and latex-freeTourniquet preferredPlaced 3 to 4 inches abovevenipuncture site*Too high veins not prominent* Too close hematoma1 minute only if longerhemoconcentration ( K,Prot,PCV)
  • 41. Blood collection near site of infusion Cause contamination / dilution Traumatic draw from vessel wall injury can elevate CK, myoglobin, and K
  • 42. 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
  • 43. Draw VolumeUnder filling Specimen dilution Erroneous PT,PTT and RBC’S morphology Inadequate anticoagulation, fibrinOverfilling formation, microclots,platelet clumping and affect instrument maintenance
  • 44. Important Liquid additives in blood collection tubeswill add a dilution factor compared with dry additives K3EDTA causes a dilution of approximately 1% to 2% compared with dry EDTA additive tube Decrease WBCs, RBCs, platelets,Hct and hemoglobin
  • 45. MIXING Insufficient mixing cause microclots Affectplatelets, Hct and hemoglobin and fibrinformation instrument probe, fluid pathobstruction and instrument down time Excessive mixing or vigorous inversions Hemolysis
  • 46. Serum clotting time Serum should be clotted before centrifugation (30-60 min) Inadequate Problem for many instruments because of latent fibrin formation ( probe clogging) and error resultProlonged contact time of serum or plasma with RBCs Exchange of Serum should compounds separated within 2 hours
  • 47. Transport Errors1- Timing 3- Transport container2- Temperature
  • 48. 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
  • 49. 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
  • 50. 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
  • 51. Transport ContainerSome samples need to be protectedFrom light as bilirubinTransport in leak proof plastic bags Or cubs