Clinical Biochemistry Notes

Learning Objectives

  • Understand key biochemical markers in blood.
  • Differentiate between plasma and serum.
  • Recognize differences among sample collection tubes.
  • Explain how sample collection methods impact laboratory results.

Purpose of Laboratory Tests

  • Diagnosis: Identifying the cause of symptoms.
  • Monitoring Disease Progression: Tracking how diseases develop over time.
  • Treatment Monitoring: Assessing effectiveness of therapies.
  • Population Screening: Detecting diseases early in healthy individuals.
  • Treatment Complications: Identifying side effects from therapies.
  • Survivability and Employability Assessment: Evaluating prognosis to inform life decisions.
  • Data Accuracy: Validating unexpected laboratory results.
  • Research: Conducting studies for scientific knowledge.
  • Preventing Malpractice: Ensuring adherence to medical standards.
  • Health Education: Training medical practitioners.
  • Nutritional Status Evaluation: Assessing health in well individuals.

Types of Patient Samples

  • Excreta/Accessible Samples:
    • Urine
    • Stool
    • Saliva and sputum
    • Semen
    • Sweat
    • Hair
    • Others
  • Internal Body Samples:
    • Blood
    • Cerebrospinal fluid (CSF)
    • Amniotic fluid
    • Biopsy Tissue
    • Bone marrow
    • Others

Biochemical Markers of Health

  • Investigate how specific biochemical molecules reflect health status.

Laboratory Organization

  • Core Lab Facility: 24/7 operation, high volume tests, automation, essential tests.
    • Electrolytes, blood gases, endocrine markers, lipids, proteins, tumor markers, vitamins, toxicology.
  • Special Chemistry: Less frequent tests, manual methods.
  • Point of Care Testing (POCT): Tests near patient site, quick results for urgent decisions.

Importance of the Test

  • Tests act as markers to differentiate health from disease.
  • Ideal markers should be:
    • Disease-specific
    • Easily measurable
    • Reflect severity of disease
    • Allow for early detection
    • Unaffected by biological variations.

Blood Collection

  • Types of Blood Sources:
    • Veins
    • Arteries
    • Skin puncture (capillary blood)
  • Collection Methods:
    • Syringe
    • Evacuated tubes with various additives.

Blood vs Plasma vs Serum

  • Whole blood: The red fluid collected.
  • Plasma: Fluid after centrifugation, includes proteins and clotting factors.
  • Serum: Fluid after clotting, lacks clotting factors.

Blood Composition

  • Separation Layers from centrifugation:
    • Plasma: 55% volume, proteins, electrolytes, nutrients.
    • Buffy Coat: White blood cells and platelets.
    • Hematocrit: Red blood cells.
  • Plasma comprises mostly water (95%).

Collection Tubes and Additives

  • Evacuated Tubes: Colour-coded, designed for specific tests.
  • Red-top tubes: No additives, collect serum after clotting.
  • Gold-top tubes: Contain gel barrier to separate serum from cells.
  • Gray-top tubes: Contain preservatives to stabilize glucose levels.
  • Green-top tubes: Use heparin as an anticoagulant.
  • Lavender-top tubes: Contain EDTA, prevent coagulation for hematology.
  • Blue-top tubes: Contain sodium citrate, for coagulation tests.
  • Brown/ Royal Blue tubes: Specially cleaned for trace metal studies.

Laboratory Test Procedure

  1. Test requested by physician
  2. Specimen collected
  3. Specimen transported to lab
  4. Accessioned in lab
  5. Processed and analyzed
  6. Results reviewed by technologist
  7. Results released to patient records.

Variations and Error Sources

  • Clinical Variations: Individual differences (age, sex, race).
  • Analytical Variations: All tests have variability; affected by:
    • Sample collection and transport
    • Laboratory test environment
    • Analysis processes.

Sources of Sample Collection Errors

  • Right tube and method must be used.
  • Specimen must be properly stored and labeled to avoid misidentification.
  • Common sources of errors include label discrepancies (patient name, ID).

Effects of Prolonged Venous Stasis

  • Increased concentrations of certain substances (e.g., proteins).
  • Decreased potassium concentration due to sieving effect.

Position of Patient During Blood Draw

  • Changes in position (supine vs standing) can affect blood volume and composition.

Hemolysis and Other Interferences

  • Hemolysis can falsely elevate potassium and affect colorimetric tests.
  • Lipemia and proteinemia may disrupt lab results.

Questions for Review

  1. What will be in the supernatant of a green-top tube post-centrifugation?
  2. Why are gray-top tubes used for glucose measurement?