MV

Chapter 1: Clinical Chemistry — Instrumentation, Proteins, Lipids, Enzymes, Electrolytes, Endocrinology, Therapeutic Drug Monitoring, Toxicology, Vitamins

Proteins and Tumor Markers

  • Protein basics
    • Proteins: amino acids linked by peptide bonds; N- and C-termini defined; nitrogen content ~16%.
    • Protein structures: primary (peptide sequence), secondary (alpha-helix, beta-sheet), tertiary (3D folding), quaternary (multimeric assemblies).
  • Protein types and functions
    • Simple proteins (globular, e.g., albumin; fibrous, e.g., collagen).
    • Conjugated proteins (prosthetic groups: metalloproteins, lipoproteins, glycoproteins, mucoproteins, nucleoproteins).
    • Functions: energy source (amino acids), maintain osmotic pressure, buffering, transport, antibodies, receptors, enzymes, etc.
  • Plasma total protein and fractions
    • Synthesis: liver (albumin, most others), plasma cells (immunoglobulins).
    • Acute-phase response: positive acute-phase proteins rise; negative acute-phase proteins include prealbumin, albumin, transferrin.
    • Reference ranges (general): Total protein ~6.5–8.3 g/dL; Albumin ~3.5–5.0 g/dL.
  • Major proteins of clinical interest
    • Prealbumin (transthyretin): nutrition status; transporter of thyroid hormones; decreased in liver disease/inflammation; increased with steroids.
    • Albumin: transport of many ligands; major plasma water-absorption contributor; low in liver disease, malnutrition; high with dehydration.
    • a1-antitrypsin: acute-phase reactant; decreased in emphysema/liver disease; increased with inflammation.
    • AFP (alpha-fetoprotein): fetal marker; maternal AFP MoM screening (15–20 weeks); increases in hepatocellular carcinoma; gestational screening in pregnancy.
    • Haptoglobin, Ceruloplasmin, a2-macroglobulin, Transferrin, CRP; REF ranges vary by protein.
    • Immunoglobulins: IgG crosses placenta; IgM produced by fetus; major classes IgA, IgD, IgE, IgG, IgM; patterns change in gammopathies.
  • Protein testing methods
    • Albumin: dye-binding (bromcresol green/purple).
    • Globulins: calculated as Total Protein − Albumin.
    • Serum protein electrophoresis: separates into albumin, alpha, beta, gamma fractions; densitometry for quantification.
    • Immunochemical methods: nephelometry, immunonephelometry, RID, immunofixation.
  • Tumor markers (concepts and major markers)
    • PSA: prostate cancer risk; measured by immunoassays; free vs total PSA; velocity concepts.
    • AFP: hepatocellular carcinoma, germ-cell tumors; maternal serum AFP for fetal anomalies.
    • hCG: pregnancy and trophoblastic tumors; measurement via immunoassay.
    • CA 125, CA 19-9, CA 15-3: ovarian and other cancers; used for monitoring therapy and recurrence.
    • CEA: colorectal and other cancers; not exclusively diagnostic; monitor disease.
  • Clinical takeaway
    • Tumor markers are more useful for staging and monitoring rather than primary diagnosis; patterns across multiple markers provide better context.

Carbohydrates

  • Glucose metabolism overview
    • Fasted glucose maintained by hepatic glycogenolysis; gluconeogenesis during prolonged fasting.
    • Renal threshold for glucose: typically 160–180 mg/dL; glucose appears in urine once threshold exceeded.
  • Hormonal regulation of glucose
    • Insulin (β-cells): promotes uptake/storage of glucose; inhibits hepatic glucose output.
    • Glucagon, cortisol, epinephrine, growth hormone, ACTH, thyroid hormones: raise blood glucose via various pathways.
  • Diabetes mellitus and related syndromes
    • Type 1: autoimmune β-cell destruction; insulin-dependent; ketoacidosis risk.
    • Type 2: insulin resistance with variable insulin secretion; obesity/age associations.
    • Gestational diabetes mellitus (GDM): screening and diagnosis via OGTT; two-step approach common.
    • Diagnosis criteria (typical): FPG \ge 126 mg/dL or 2-h plasma glucose \ge 200 mg/dL (OGTT); IFG 100–125 mg/dL; HbA1c 6.5% threshold (per guidelines vary by era).
  • HbA1c and fructosamine
    • HbA1c reflects average glucose over ~2–3 months (RBC lifespan ~120 days).
    • Fructosamine reflects ~2–3 weeks of glucose levels.
  • Glucose measurement methods
    • Glucose oxidase and hexokinase as primary enzymatic methods; OGTT (75 g or 100 g) had standardized protocols; pediatrics and pregnancy-specific considerations.
  • Lipid-glucose interplay and monitoring in diabetes
    • Microalbumin testing for nephropathy risk; glycemia control correlates with risk reduction of complications.

Lipids and Lipoproteins

  • Lipid structure and transport
    • Fatty acids, triglycerides, cholesterol, phospholipids; lipoproteins transport lipids in blood: chylomicrons, VLDL, IDL, LDL, HDL; Lp(a).
  • Lipoprotein classes and composition
    • Chylomicrons: largest, highest TG; HDL: smallest TG, highest density; LDL: main cholesterol carrier; VLDL and IDL: intermediate forms; apolipoproteins (Apo A-1, Apo B-100, Lp(a)).
  • Clinical significance and guidelines
    • ATP III-style reference ranges: Total cholesterol, HDL, LDL, triglycerides; risk stratification for coronary heart disease (CAD).
  • Lipid testing methodologies
    • HDL: precipitation or direct homogeneous methods; LDL: Friedewald equation (not valid if TG > 400 mg/dL): \text{LDL} = \text{TC} - \text{(HDL} + \frac{\text{TG}}{5} \text{)}
    • Direct/assay LDL measurements; triglyceride enzymatic methods; enzymatic cholesterol assays (cholesteryl esterase, cholesterol oxidase, peroxidase).
  • Apolipoproteins and Lp(a)
    • Apo A-1 (HDL component, anti-atherogenic); Apo B-100 (LDL; CAD risk); Lp(a) a risk factor for atherosclerosis.
  • Lipid disorders and familial hyperlip