Biochemical Markers for Disease Diagnosis

Biochem Markers: Cardiac & Basics - Diagnostic Detectives

• Biochemical Marker: Substance indicating biological state (normal, disease, drug response).
• Ideal Marker Traits:
  • High specificity & sensitivity.
  • Organ-specific.
  • Prognostic value.
  • Easy, rapid, cost-effective assay.
  • Short half-life for monitoring.
• Cardiac Markers:
  • Troponins (cTnI, cTnT): Key for MI diagnosis.
    • Rise: 2-4 hrs; Peak: cTnI 12-24 hrs, cTnT 24-48 hrs.
    • Duration: cTnI 7-10 days, cTnT 10-14 days.
  • CK-MB:
    • Rise: 3-6 hrs; Peak: 12-24 hrs; Duration: 2-3 days.
    • For re-infarction. Index: $(CK-MB / Total CK) \times 100 > \textbf{6}%$.
  • Myoglobin: Earliest ( 1-2 hrs), non-specific.
  • BNP/NT-proBNP: For Heart Failure. BNP < 100 pg/mL excludes acute HF.
  • LDH: LDH1 > LDH2 (flipped pattern) in MI; late marker.

⭐ cTnI is highly cardiospecific; cTnT may be elevated in renal failure without acute cardiac injury.

Biochem Markers: Liver & Renal - System Scanners

Liver Markers (LFTs):

• ALT (SGPT): Liver-specific; ↑ hepatocellular injury.
• AST (SGOT): Liver, heart, muscle; ↑ liver injury, MI.
  • AST/ALT >2: Alcoholic liver disease.
  • AST/ALT <1: Viral hepatitis.
• ALP: Liver (cholestasis), bone; ↑ cholestasis, bone disease.
• GGT: Sensitive: alcohol liver damage, cholestasis.
• Bilirubin (Total/Direct):
  • ↑ Indirect: Pre-hepatic (hemolysis).
  • ↑ Direct: Post-hepatic (obstruction).
• Albumin: ↓ chronic liver disease, nephrotic syn.; liver synth. function.

Renal Markers (RFTs):

• Serum Creatinine: Muscle origin; ↑ renal impairment. (Normal: 0.6-1.2 mg/dL)
• BUN: Protein metabolism; ↑ renal failure, dehydration. (N: 7-20 mg/dL)
• BUN/Creatinine Ratio:

  • 20:1: Pre-renal.

  • <10:1: Intra-renal.
• eGFR: Best kidney function index. (N: >90 mL/min/1.73m²)
• Microalbuminuria: 30-300 mg/day; early diabetic nephropathy.

⭐ AST/ALT ratio (De Ritis ratio): >2 strongly suggests alcoholic liver disease, while a ratio <1 is common in viral hepatitis or NAFLD.

Biochem Markers: Tumor, Endocrine, Genetic - Cellular Secrets

• Tumor Markers (Neoplasia)
  • Alpha-fetoprotein (AFP): ↑ Hepatocellular carcinoma (HCC), non-seminomatous germ cell tumors (NSGCT).
  • Carcinoembryonic Antigen (CEA): ↑ Colorectal, pancreatic, lung, breast cancer. Monitor recurrence, not for screening.
  • Prostate-Specific Antigen (PSA): ↑ Prostate cancer, BPH. Screening & monitoring. Normal < 4 ng/mL.
  • CA-125: ↑ Ovarian cancer (epithelial). Monitor therapy response & recurrence.
  • CA 19-9: ↑ Pancreatic cancer, cholangiocarcinoma.
  • Human Chorionic Gonadotropin (hCG): ↑ Trophoblastic tumors (choriocarcinoma, hydatidiform mole), testicular tumors.
  • Calcitonin: ↑ Medullary thyroid carcinoma.
• Endocrine Disorders
  • HbA1c (Glycated Hemoglobin): Long-term glycemic control in Diabetes Mellitus (DM). Target < 7%. Diagnosis: ≥ 6.5%.
  • Thyroid Stimulating Hormone (TSH): Best initial test for thyroid function. ↑ Primary hypothyroidism, ↓ Primary hyperthyroidism.
• Genetic Disorders
  • Phenylalanine (plasma): ↑ Phenylketonuria (PKU). Essential for newborn screening.
  • Homogentisic acid (urine): ↑ Alkaptonuria.

⭐ AFP levels > 400-500 ng/mL are highly suggestive of hepatocellular carcinoma in at-risk patients (e.g., cirrhosis).

High‑Yield Points - ⚡ Biggest Takeaways

• Troponins (I & T): Gold standard for Myocardial Infarction (MI) diagnosis.
• ALT: More specific marker for hepatocellular injury than AST.
• Serum Creatinine & eGFR: Key indicators of kidney function.
• HbA1c: Reflects average blood glucose over 2-3 months; crucial for diabetes management.
• Tumor markers (e.g., PSA, AFP, CA-125): Aid in cancer diagnosis, prognosis, and monitoring.
• Lipase: Preferred over Amylase for diagnosing acute pancreatitis due to higher specificity.