Makindo Medical Notes

What CEA is 🧬

• Glycoprotein (~180–200 kDa) involved in cell adhesion during fetal life; expression is low in healthy adults.
• Units: ng/mL ≡ μg/L (same thing).
• Half-life: ~3–7 days ➜ after curative surgery, CEA should trend down toward normal within ~4–6 weeks if no residual disease.

Typical reference ranges 📏

• Non-smokers: 0–2.5 ng/mL (μg/L)
• Smokers: often slightly higher, up to ~5 ng/mL
• “Elevated”: >5 ng/mL is commonly flagged (assay- and lab-specific; always check your lab’s range).

Tip: Always try to use the same laboratory/assay for serial monitoring—inter-assay differences can shift values.

When to order CEA (the useful use-cases) 🎯

• Before CRC surgery/therapy: Establish a baseline (prognostic & helps future comparisons).
• After curative CRC resection: Serial monitoring to detect recurrence (trend matters more than a single value).
• Metastatic CRC on treatment: Track response alongside imaging and clinical review.
• Medullary thyroid carcinoma (MTC): Follow alongside calcitonin (CEA can rise with tumor dedifferentiation).

Not recommended for general population screening or as a one-off “cancer check.”

How to interpret a rise 📈

• Trends & doubling time: A confirmed upward trend across ≥2–3 measurements is more concerning than a single bump. Faster “CEA doubling time” can suggest more aggressive or recurrent disease.
• Rule of thumb thresholds (CRC):
  • Persistently >10 ng/mL → higher suspicion for recurrence/metastases (but not diagnostic).
  • >20 ng/mL → often associated with metastatic disease, especially to the liver—yet false positives exist.
• Non-producers: A subset of CRCs do not make CEA—levels may stay normal despite active disease.

What else elevates CEA? (Cancer & non-cancer) 🧩

• Cancers: Colorectal (most common use), pancreatic, gastric, cholangiocarcinoma, lung, breast, ovarian, liver, medullary thyroid, prostate.
• Benign: Heavy smoking, chronic liver disease/cholestasis, pancreatitis, inflammatory bowel disease, peptic ulcer disease, COPD, infections, hypothyroidism (usually mild elevations).

Pearl: Because the liver clears CEA, cholestasis/liver mets can raise values independently of tumor burden.

Follow-up cadence (typical CRC practice) ⏱️

• After curative resection: many protocols check CEA every 3–6 months for 2–3 years, then every 6 months to 5 years (integrated with clinical review and appropriate imaging/colonoscopy). Use local/national guidelines.

Performance at a glance 🔎

• Diagnosis/screening: Limited sensitivity/specificity → not recommended.
• Recurrence detection: Moderate sensitivity; best as part of a multimodal follow-up strategy (history, exam, imaging, colonoscopy).
• Prognosis: Very high pre-op levels may correlate with worse outcomes in CRC, but management decisions hinge on comprehensive staging and pathology.

Pre-analytical & assay caveats ⚠️

• Biotin supplements (high-dose) can interfere with some immunoassays → pause 24–48h if safe, per lab guidance.
• Hemolysis/lipemia/assay drift can affect results—interpret alongside clinical picture and imaging.
• If a result seems discordant, repeat and confirm with the same lab before acting.

Bottom line 🧠

CEA is a monitoring tool, not a stand-alone cancer test. Use it to follow known CEA-secreting tumors—especially colorectal cancer—prefer trends over single values, and always interpret in context of symptoms, exam, imaging, and histology.

Reference ranges (recap) 📚

• Non-smokers: 0–2.5 ng/mL (μg/L)
• Smokers: up to ~5 ng/mL may be seen
• “Elevated” threshold: commonly >5 ng/mL (check your lab)

Further reading

• Major society guidance (e.g., NCCN/ASCO/ESMO) on CRC follow-up incorporates serial CEA with clinical assessment and imaging; consult current local protocols for exact intervals and thresholds.