Diagnosing colorectal cancer involves a combination of medical history evaluation, physical exams, laboratory tests, and various imaging techniques. Here are the primary methods used to diagnose colorectal cancer:

1. Screening Tests

a. Fecal Occult Blood Test (FOBT)

• Description: This test checks for hidden (occult) blood in the stool, which can be a sign of cancer or large polyps.
• Types:
  • Guaiac FOBT (gFOBT): Uses a chemical reaction to detect blood in the stool.
  • Fecal Immunochemical Test (FIT): Uses antibodies to detect blood in the stool.
• Sources: American Cancer Society, Mayo Clinic

b. Stool DNA Test

• Description: This test looks for certain DNA mutations and blood in the stool that may indicate cancer.
• Example: Cologuard is a commonly used stool DNA test.
• Sources: Mayo Clinic, American Cancer Society

2. Imaging Tests

a. Colonoscopy

• Description: A procedure in which a long, flexible tube with a camera (colonoscope) is inserted through the rectum to examine the entire colon and rectum.
• Purpose: Allows for the detection and removal of polyps and biopsy of suspicious areas.
• Sources: National Cancer Institute, American Cancer Society

b. Flexible Sigmoidoscopy

• Description: Similar to a colonoscopy, but only examines the rectum and lower part of the colon.
• Purpose: Useful for detecting cancer and polyps in the lower colon.
• Sources: Mayo Clinic, American Cancer Society

c. CT Colonography (Virtual Colonoscopy)

• Description: A CT scan of the colon and rectum to produce detailed images.
• Purpose: Non-invasive alternative to colonoscopy for detecting polyps and cancer.
• Sources: American Cancer Society, National Cancer Institute

3. Biopsy

• Description: The removal of a small piece of tissue for examination under a microscope.
• Procedure: Performed during a colonoscopy or surgery if a suspicious area is found.
• Purpose: To confirm the presence of cancer cells and determine the type and aggressiveness of the cancer.
• Sources: American Cancer Society, Mayo Clinic

4. Laboratory Tests

a. Blood Tests

• Complete Blood Count (CBC): To check for anemia, which can be caused by bleeding from a tumor.
• Liver Function Tests: To assess whether cancer has spread to the liver.
• Tumor Markers: Tests for substances like carcinoembryonic antigen (CEA) that can be elevated in colorectal cancer.
• Sources: National Cancer Institute, American Cancer Society

Conclusion

Diagnosing colorectal cancer typically involves a combination of screening tests, imaging procedures, biopsies, and laboratory tests. Early detection through regular screening is crucial for effective treatment and improved outcomes.

Further Reading

• American Cancer Society: How Colorectal Cancer Is Diagnosed
• Mayo Clinic: Colon Cancer Diagnosis
• National Cancer Institute: Colorectal Cancer Screening (PDQ®)–Patient Version

These resources provide comprehensive information on the various methods used to diagnose colorectal cancer.