2. Patient preparation before sampling. Proper method to carry out blood (venous, capillary) and urine collection. Type of tubes.

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Patient preparation

  • Preanalysis
    • Clinical question
    • Request for analyses
    • Patient sampling
    • Transit to lab
  • Analysis
  • Postanalysis
    • Collection
    • Interpretation
    • Reporting
    • Answer

Urinary sample collection

Proper sample collection is essential to maintain as high sensitivity and specificity as possible. A sterile container for urine collection is obligatory to prevent contamination. The patient should not provide a sample if they've peed in the previous 4 hours, as in these cases the urine is "too fresh" to show signs of bacterial infection. Morning urine is usually best. The male should withdraw the foreskin and the female should spread the labia when making the sample, to prevent contamination. The initial urine should be discarded; mid-stream urine should be used.

Sources of errors

Preanalytical errors are errors which occur in the preanalytical phase, including ordering the test, patient identification, patient preparation ahead of analysis, sample collection, and sample transportation to the lab. Preanalytical errors account for 80% of all errors of laboratory investigations.

Preanalytical factors:

  • Preparation of patient
    • Identification
    • Diet
      • Fasting affects glucose, triglycerides
    • Drugs
    • Smoking
    • Pregnancy
    • Exercise
      • Epinephrine, cortisol increase
    • Dehydration
    • Infection
      • Iron parameters wrong
      • TSH, thyroid hormones wrong
  • Sample taking
    • Posture
      • Increased in standing position: RBC, WBC, Hb, HTC, …
    • Time of sample taking
      • Cortisol highest in morning
      • TSH highest in evening
    • Strangulation
      • Max 1 min!
    • Simultaneous infusions
    • Identification of the sample
    • Patting the vein
    • Shaking the tubes too much
    • Correct tube
    • Correct order
    • Correct vessel
    • Correct filling of tube
  • Sample preparation
    • Haemolysis
      • Increased LDH, K+
      • Decreased RBC
      • Interferes with photometry, haemostasis
    • Clotting
    • Lipaemia
    • Centrifugation
    • The elapsed time from sample taking
      • Blood gas: max 30 min
    • Temperature
      • Usually room temperature
      • Store on ice: ACTH, renin, aldosterone
    • Sunlight
    • Labelling
    • Delivery
  • Errors in case of urine collection:
    • First morning urine
      • Unsanitary
      • Clean container
      • Duration of sample storage
    • 24-hour urine
      • Many possible errors

Types of tubes

Order Tube Additive Colour Blood product Use
0. Blood culture – – Culture
1. Haemostasis tube Sodium citrate Light blue Plasma Coagulation studies
2. Sedimentation tube Sodium citrate Black Plasma ESR
3. Plain tube Nothing Red Serum Biochemistry, immunology, serology
4. Serum tube Gel + clot activator Yellow Serum Biochemistry, immunology, serology
5. Heparin tube Lithium heparin Green Plasma Blood gas values
6. EDTA tube EDTA Purple Plasma CBC
7. Glycolysis inhibitor Fluoride, oxalate Grey Plasma Glucose, lactate