Biological Sample Collection and Laboratory Practice

Types of Biological Specimen

  • Common specimens analysed in clinical laboratories: Whole blood, Serum, Plasma, Urine, Feces, and various fluids (Pleural, Ascitic, Cerebrospinal fluid [CSF], Synovial, Pericardial, and Amniotic).
  • Plasma: Obtained by centrifugation of blood with added anticoagulant; contains all coagulation factors except calcium ions.
  • Serum: Obtained after blood clotted; does not contain clotting factors.

Blood Sample Collection

  • Venipuncture (Phlebotomy): The process of collecting venous blood. Methods include:     * Vacuum evacuated tube system (ETS): The preferred method using a needle, holder, and color-coded tubes.     * Needle and syringe: Blood is later transferred to tubes.     * Winged infusion set: Used for small veins, such as in pediatric patients.

Vacuum Evacuated Tubes and Additives

  • Green top: Contains Sodium or Lithium heparin. Used for ABG analysis and osmotic fragility tests.
  • Gray top: Contains Potassium oxalate (anticoagulant) and Sodium fluoride (antiglycolytic agent inhibiting enolase). Used for blood glucose estimation.
  • Light blue top: Contains Sodium citrate. Used for coagulation studies: PT (Prothrombin time), TT (Thrombin time), and factor assays.
  • Purple top: Contains EDTA. Used for hematology (Complete blood count, blood film, HbA1C, ESR) and blood banking.
  • Red top: No additive or silica particles (clot activator). Used for biochemistry serum tests, blood bank, and serology (Hepatitis, HIV, rheumatoid factor).
  • Royal blue top: Sodium heparin and Sodium EDTA. Used for trace elements (zinc, copper, lead, and mercury).
  • Yellow top: Contains SPS (Sodium polyanethol sulfonate) or ACD (acid citrate dextrose). Used for blood/body fluid cultures, HLA, and DNA testing.

Order of Draw

  1. Sterile tube (blood culture).
  2. Coagulation tube (Blue top).
  3. Serum tube (Red top or yellow top).
  4. Heparin tube (Green top).
  5. EDTA tube (Purple top).
  6. Glycolytic inhibitor tube (Gray top).

Urine Sample Collection and Types

  • Random Sample: Collected anytime; used for routine screening.
  • First Morning Sample: Most concentrated; preferred for microscopic examination, protein, and HCG detection.
  • Timed (24-hour) Specimens: Collected in a 1000−5000 mL1000-5000\,mL container with preservatives for creatinine clearance and hormone studies.
  • Clean-Catch Midstream: Genitalia are cleaned before collection in a sterile container; used for bacteriological culture.
  • Catheterized Specimen: Collected via catheter from seriously-ill patients for microbiological examination.

Urine Preservation

  • Urine becomes more alkaline after collection due to bacterial metabolism.
  • Preservatives include: Refrigeration, 6N HCl6N\,HCl, Boric acid, Formalin (best for sediments), Sodium fluoride, Phenol, Toluene, Thymol, and commercial tablets.

Questions & Discussion

  1. Enumerate different types of biological samples.
  2. Give methods of collection of blood sample.
  3. Describe color-coded vacuum evacuated tubes, their additives and uses in laboratory.
  4. Describe types of urine samples.
  5. Describe collection of different types of urine samples.
  6. Write additives used in grey evacuated tube and its importance.
  7. Enumerate different types of urine preservatives.
  8. What are vacutainer tubes?
  9. Mention the different vacutainer tubes and their uses.
  10. What is the difference between plasma and serum?