What causes low iron saturation, elevated Carcinoembryonic Antigen (CEA) tumor marker, and consistently elevated platelet count (thrombocytosis)?

Colorectal Cancer Until Proven Otherwise

The combination of low iron saturation, elevated CEA, and persistent thrombocytosis strongly suggests colorectal carcinoma, particularly right-sided colon cancer, and warrants urgent colonoscopy and imaging evaluation.

Primary Diagnostic Consideration

This triad of findings is highly characteristic of gastrointestinal malignancy, specifically colorectal cancer:

• Iron deficiency from chronic blood loss occurs in 51% of colorectal cancer patients, with low ferritin levels found in 60% of those tested 1
• Elevated CEA is present in approximately 45% of colorectal cancer cases and is produced by 90% of colorectal tumors 1, 2
• Thrombocytosis commonly accompanies malignancy as a paraneoplastic phenomenon, particularly with chronic blood loss and inflammation

High-Risk Features for Right-Sided Colon Cancer

The pattern you describe is particularly concerning for proximal (right-sided) colon cancer because:

• Right colon tumors cause significantly more iron deficiency than left-sided lesions due to chronic occult bleeding 1, 3
• Female patients, those with right colon tumors, and tumors ≥3 cm are at highest risk for iron deficiency anemia 1
• Serum hemoglobin, iron, and ferritin are all significantly lower when tumors exceed 3 cm in diameter 3

Clinical Significance of Each Finding

Low Iron Saturation

• Gastrointestinal malignancy is a critical cause of chronic iron deficiency 1
• The larger the tumor (>3 cm), the more severe the iron deficiency 3
• Proximal colon cancers bleed more chronically than distal lesions, causing more profound iron depletion 3

Elevated CEA

• While CEA lacks sensitivity for early-stage screening, an elevated level in the context of iron deficiency is highly suspicious for colorectal cancer 2, 4
• CEA >8 ng/ml is highly suggestive of active malignancy, even without clinical symptoms 5
• Approximately 90% of patients with progressive colorectal cancer will show CEA elevation during their disease course 5

Persistent Thrombocytosis

• Reactive thrombocytosis occurs with chronic inflammation, iron deficiency, and malignancy
• The combination with the other findings makes malignancy the primary concern rather than isolated reactive causes

Immediate Workup Required

Urgent colonoscopy with biopsy is the definitive diagnostic test 1, 3

Additional essential studies:

• CT chest/abdomen/pelvis to assess for metastatic disease, as elevated CEA correlates with advanced stage 2, 5
• Complete iron panel including serum iron, TIBC, and ferritin to confirm iron deficiency 1, 3
• Baseline CEA level for future monitoring if cancer is confirmed 2

Critical Pitfalls to Avoid

• Do not attribute iron deficiency to dietary causes in adults without first excluding GI malignancy, especially with concurrent CEA elevation 1
• Do not delay colonoscopy for empiric iron supplementation trials—this combination demands immediate investigation 1, 3
• Do not assume benign causes of thrombocytosis when other red flags are present
• Right-sided tumors are easily missed on flexible sigmoidoscopy; full colonoscopy is mandatory 1, 3

Prognostic Implications if Cancer Confirmed

• Preoperative CEA elevation correlates with reduced overall survival and is a poor prognostic sign 2
• Tumor size >3 cm and right colon location indicate higher likelihood of significant disease burden 1, 3
• If CEA fails to normalize after surgical resection, this indicates inadequate resection or occult metastatic disease 2