11-CLINICAL-CHEMISTRY-version-2.0

Clinical Chemistry

Learning Objectives

• Understand clinical chemistry basics

• Identify different analytical techniques used in the lab

• Describe routinely requested clinical chemistry assays

What is Clinical Chemistry?

• Branch of medical science analyzing biological materials (usually bodily fluids) for diagnosis

Basic Analytical Techniques

Spectrophotometry

• Measures light intensity at specific wavelengths

• Determines concentration of colored solutions

• Utilizes prisms/gratings to isolate light range

• Types of light used:

  • Visible light

  • Ultraviolet light (< 400 nm)

  • Infrared light (> 700 nm)

Nephelometry

• Measures light scattered by a substance at right angles

• Depends on particle size and wavelength

Turbidimetry

• Measures light blocked by particle suspension (absorbance)

• Dependent on particle size and concentration

Electrophoresis

• Charged molecules migrate through an electrical field

• Cations move to cathode; Anions move to anode

Flame Emission Spectrophotometry

• Measures light emitted by excited atoms

• Characteristic colors for elements:

  • Sodium: intense yellow

  • Potassium: violet

  • Calcium: brick red

Atomic Absorption Spectrophotometry

• Measures light absorbed by ground state atoms

• Commonly measures trace metal concentrations

• Uses hollow cathode lamp as light source

Routinely Tested Clinical Chemistry Assays

Blood Glucose

• Primary energy source; increases after eating

• Short-term: Liver and skeletal muscles; Long-term: Adipose tissues

• Can appear in urine if renal threshold exceeded (160-180 mg/dL)

• Clinical significance: Diabetes mellitus (defect in insulin production)

• Tests include FBS, RBS, OGTT, 2HPPBS, and HbA1C for long-term glucose measurement

Blood Lipid Profile

• Lipids: Insoluble in water, soluble in organic solvents; serve as secondary energy source

• Classification:

  • Fatty Acids: Simplest form, not routinely measured

  • Triglycerides: Storage form, increase serum turbidity post-meal

  • Cholesterol: Steroid alcohol, important for hormones and digestion

  • Phospholipids: Abundant, evaluated for fetal-lung maturity

  • Lipoproteins: Transport lipids, classified by density (HDL, LDL, VLDL)

Kidney (Renal) Function Tests

• Creatinine: Waste product of muscle metabolism; increased levels indicate renal issues

• Blood Urea Nitrogen (BUN): Indicator of protein metabolism; low/high levels suggest various conditions

• Glomerular Filtration Rate (GFR): Assess kidney function, used for various risk factors

Liver Function Tests

• Bilirubin: Breakdown product of red blood cells, two forms (unconjugated and conjugated)

• Liver Enzymes:

  • AST, ALT (liver-specific), De Ritis Ratio for hepatic disorders

  • ALP, GGT for liver/bone disease and alcohol-related damage

• Total Serum Proteins: Measures albumin and globulin; low levels suggest liver/kidney issues

Cardiac Function Tests

• Evaluate heart health, especially after myocardial infarction

• Troponin test: Most specific for myocardial damage

• Myoglobin: Cardiac biomarker alongside troponin

Tumor Markers (Special Chemistry Tests)

• Biomarkers indicating cancerous conditions:

  • AFP (hepatocellular carcinoma)

  • CEA (gastrointestinal cancer)

  • PSA (prostate cancer)

  • hCG (gestational disease)

  • NSE, CA 125, CA 19-9, CA 15-3, Calcitonin, and Desmin for various cancers.