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Sample Collection


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Sample Collection Procedure

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Sample Collection

  1. 1. RAJEEV
  2. 2. • SCENE 1 :- You have to collect blood for glucose estimation from a hemiplegic patient with the right healthy arm running an i.v dextrose drip. Which site will you choose ? • SCENE 2 :- You have to transport a 24 hr urine sample for estimation of Uric acid .Which preservative will you use ? • SCENE 3 :- You have to send samples for study of cell morphology. Which container will you use ?
  3. 3. The Quality Assurance Cycle •Data and Lab Management •Customer Service Patient/Client Prep Sample Collection Sample Receipt and Accessioning Sample Transport Quality Control Record Keeping Reporting Personnel Competency Test Evaluations Testing
  4. 4. PRE-ANALYTICAL VARIABLES – Proper Instructions to patient – Patient preparation – Sample collection – Sample transportation – Sample storage – Sample preparation
  5. 5. TYPES OF BIOLOGICAL SAMPLES – BLOOD – WHOLE BLOOD – SERUM – PLASMA – URINE – FECES – OTHER BODY FLUIDS LIKE saliva, spinal, synovial, amniotic, pleural, pericardial and ascitic fluid
  6. 6. BLOOD The process of collecting a blood sample is called as phlebotomy. -VENOUS -ARTERIAL -CAPILLARY
  8. 8. • LOCATION – • VEIN OF CHOICE-median cubital vein in the antecubital fossa as the vein is large and very close to skin • Veins on back of the hand or ankle (AVOID in diabetics and patients with poor circulation) • Ankle • In IPD it is advisable to collect blood during insertion of iv- channel. • If it is absolutely necessary to collect blood from an arm running fluids - SHUT OFF fluids for 3 minutes and discard first 5ml of blood • Use a site below infusion site as retrograde blood flow through veins doesn’t occur.
  9. 9. • PATIENT POSITION:- – patient should be comfortable :seated or supine . – Never perform on a standing patient. – Arm to be extended straight from wrist to shoulder. • WEAR PROTECTIVE EQUIPMENT e.g. gloves, gown , masks (preventing aerosol transmission) to prevent transmission of infection from patient Note - do enquire about latex allergy as gloves, tourniquets are commonly made of latex • NEEDLES- • 19-22 gauze commonly used .(larger the gauze- smaller the bore ). • For children use 22-23 . • If collecting a larger volume say 20 – 30 ml use 18or wider bore needle.
  10. 10. • TO AVOID VENEPUNCTURE ON A PARTICULAR ARM IF – i.v fluid running on that side – Hemiplegia or other sensory loss ( RISK OF AN INFECTED ARM AND GANGRENE LATER –PATIENT WILL NOT FEEL PAIN) – infections, cellulitis – arterio-venous fistula – AVOID repeated aspiration from a single arm – sclerosed veins : repeated transfusions , chemotherapy –LEAVE IT TO THE SPECIALIST ONLY TRY OTHER ARM, ANKLE VEINS, FEMORAL –TAP
  11. 11. • 2) SITE PREPARATION: - Disinfect with a) prepackaged alcohol b) Gauze pad saturated with 70% isopropanol c) benzalkonium chloride solution 1:750 • Cleaning of puncture site must be done in a circular motion and from the site outward. • Skin should be allowed to dry as alcohol can cause hemolysis and interfere with results.
  12. 12. • 3) TIMING – The time at which a specimen is obtained is important for constituents that have diurnal variation e.g. cortisol and samples of therapeutic drug monitoring . • Timing also very important for measurement of glucose and alcohol.( medicolegal importance- concentration may change later) • Types of timed samples:- – FASTING SAMPLE is best for biochemical investigations (12- 14 hrs or overnight fast) – POST PRANDIAL SAMPLE is taken 2 hours after a meal – RANDOM SAMPLE can be taken anytime.
  13. 13. 4) VENOUS OCLUSION – • It is done to distend the veins. • Place a tourniquet 4-6inches above an intended puncture. • A BP cuff can be used ; the pressure kept not more than 60 mm Hg. • It should not be kept for more than one minute – Decreased pH – increased lactate – increased proteins – increased ionized calcium – increased potassium • Pumping and taping of hand to be avoided.
  14. 14. • 5) ASPIRATION: - RULE :- ASPIRATE SLOWLY – Use an evacuated blood tube (VACUTAINER) • Direct fill • Advantages of evacuated blood tube – more convenient, easier to use • Drawback- costlier • If using a syringe maintain the 15 degree contact angle . ASPIRATE SLOWLY
  15. 15. • 6) SEAL PUNCTURE SITE USING A STERILE SWAB • 7) LABELLING: - Label after every collection . No batch labelling ( Put the sticker or write neatly on tube after collecting each sample only) • 8) DESTROY AND DISCARD NEEDLE: - USE A NEEDLE CUTTER • 9) AUTOCLAVE all disposables
  16. 16. • ARTERIAL BLOOD:- Use :- Blood gas analysis • Required specially training and performed by doctors or specially trained technicians only. • SITES: - RADIAL ARTERY, BRACHIAL ARTERY, FEMORAL ARTERY • TRANSPORT TO POINT OF TESTING :- – USE HEPARINIZED SYRINGE – !!HURRY !! – !!!EVERY SEC VALUES CHANGE !!!
  17. 17. • CAPILLARY BLOOD:- Skin is punctured with a lancet and a small volume of blood is collected . Uses:- a) Limited sample volume e.g. paediatric ward. b) Repeated venepunctures have caused severe vein damage c) Burns or bandaged areas- veins are not available for venepuncture d) Blood collected on special filter papers for neonatal screening and molecular genetics testing • SITES:- – tip of a finger – An ear-lobe – Heel or big toe of infants
  18. 18. STEPS:- • Clean site • Puncture with a sharp stab but not deeper than 2.5cm to avoid contact with bone • Use different site for each puncture to prevent infection • Don’t press or massage as it causes tissue debris and tissue fluid comes out – it is not same as plasma • First drop of blood is wiped off and the subsequent drops are collected in appropriate collection tubes • Fill rapidly as site will clot
  19. 19. Patient preparation – • Preparation of Patient for OGTT:- • The Patient is instructed to have good • carbohydrate diet for 3 days prior to the test. • Diet containing about 30-50gm of carbohydrate should be taken on the evening prior to the test. • Patient should avoid oral hypoglycemics for at least 2 days prior. • No Strenuous exercise on previous day. • Patient should be on 12 hr fast 8PM to 8 AM next morning. NO TEA –COFFEE – BISCUITS etc . • No smoking during the test
  20. 20. • Preparation of Patient for LIPID PROFILE :- • The Patient is instructed to have normal diet for 3 days prior to the test. No extra butter/ghee or other oils in food. Avoid meat and eggs day before testing. • Patient should avoid oral cholesterol lowering medicines (eg.STATINS)for at least 2 days prior. • No Strenuous exercise on previous day. • Patient should be on 12 hr fast 8PM to 8 AM next morning. ( NO TEA – COFFEE IN MORINING) • No smoking during the test .
  21. 21. Containers and preservatives for blood • PLAIN BULB – No anticoagulants .Used for all investigations on serum eg.enzymes, bilirubin, uric acid etc • FLUORIDE BULB – Potassium oxalate and sodium fluoride ( 3 :1) • Sodium fluoride inhibits Glycolytic enzyme ENOLASE. Potassium oxalate forms insoluble complexes with Ca+2 and prevents coagulation. • Use: Blood sugar estimation • CHEMISTRY BULB – Potassium oxalate - 20 mg/ 10 ml blood .It forms insoluble complexes with calcium ions and prevents coagulation • Use: Urea estimation • CITRATE BULB – Sodium citrate - 60 mg/10ml blood. Citrate converts Ca+2 to a soluble non-ionized form • Use: Prothrombin time, Blood grouping, ESR .Should not be used to determine calcium
  22. 22. • WINTROBE BULB – Ammonium oxalate and Potassium oxalate - forms insoluble complexes with Ca+2 and prevents coagulation. Use: Routine haematological investigations, cell morphology of body fluids. It should not be used to measure urea by urease method as it contains ammonium oxalate. • PARAFFIN COATED – Inner surface coated with paraffin to make surface smooth and prevents cell lysis. Use: to study cell morphology of body fluids. • EDTA BULB- EDTA - 20mg/10ml.It chelates divalent cations like Ca+2, Mg+2 Use: Platelet count, bone marrow examination, isolation of genomic DNA • HEPARIN BULB- Heparin – inhibits factors IX and XI and also binds anti -Thrombin III and increases its activity. (2mg/10 ml) Use: Arterial blood gas analysis and osmotic fragility test. It can be used for a wide range of analytes but it is costly. It inhibits enzyme ACID PHOSPHATASE and unsuitable for its assay.
  23. 23. • Note – While mixing anti-coagulant with sample it is important not to shake vigorously as this causes hemolysis.
  24. 24. URINE COLLECTION • TYPES OF SPECIMENS:- • RANDOM – obtained at anytime of the day • EARLY MORNING SAMPLE – A clean, early morning fasting sample is the most preferred sample for detection of abnormal constituents like proteins, or compounds like HCG. • DOUBLE VOIDED SPECIMEN is used in GTT. It is the urine excreted during a timed period after a complete emptying of bladder • MID-STREAM SAMPLE- For bacteriological examinations, the first 10 ml of voided urine is discarded then urine is collected.External genitalia must be cleaned properly for such collection. • CATHETERISATION of the bladder through the urethra for urine collection is carried out only in special circumstances, i.e., in a comatose or confused patient. This procedure risks introducing infection and traumatizing the urethra and bladder, thus producing iatrogenic infection or hematuria.
  25. 25. • Suprapubic aspiration of urine from bladder:- – Urethral injury( eg Ruptured Urethra ) – take sample from suprapubic catheter – Urethral obstruction (Tumors, Strictures etc causing complete obstruction) – Prolonged catheterization especially for Urine culture and sensitivity .
  26. 26. • 24-HOUR SAMPLE - Obtained by collecting urine excreted in 24 hours. E.g. 8am of one day to 8am of next day discarding early morning sample of first day. (Volume - 1200 to 1500ml.) URINE PRESERVATIVES:- • Substances added to urine to reduce bacterial action or chemical decomposition or to solubilize constituents that might precipitate out of solution. Commonly used are :- • HCl -6mol/L -30ml per 24 hour collection (pH below 3) • Na2CO3 ,NaOH is used to preserve specimens for Uric acid, urobilinogen and porphyrins. (pH – 8- 9). Uric acid will form clump like precipitate with HCl.
  27. 27. Toluene and light petroleum are also good preservatives but as they are lighter than urine they float on urine and contaminate pipettes during processing. Others; - Thymol, Acetic acid, Na2CO3 ,HNO3 , Boric acid.
  28. 28. • OTHER BODY FLUIDS CSF • Uses Meningitis, CVA, demyelinating diseases like multiple sclerosis, meningeal involvement in malignant disease • Procedure – Lumber Puncture • Contraindications of lumbar puncture – A very high intra-cranial pressure in infants and children can cause instant death if LP is carried out as CSF gushes out too fast and brain stem herniation occurs- check for PAPLLOEDEMA
  29. 29. Ascitic fluid Uses – Ascites of any cause – cirrhosis, peritonitis etc Procedure -Abdominal tap at most dependent portion at maximum dullness Pleural fluid and Pericardial fluid – Pleural and Pericardial effusion Amniotic fluid Uses – prenatal diagnosis of congenital disorders, assessment of fetal maturity & Rh iso immunization Procedure -Amniocentesis
  30. 30. FAECES • ANALYSED FOR THE FOLLOWING – 1) FAECAL FAT – obstructive jaundice and malabsorption 2) PARASITES – microscopy 3) HEME AND OCCULT BLOOD – for GI bleeding 4) FAECAL NITROGEN- malabsorption • Care to be taken to prevent contamination with urine during collection. • Usually fresh specimens to be used to avoid need for preservation.