Mrs. Simpson, a 38-year-old female, presented for biopsy and excision of a recently discovered lump in her right breast

Mrs. Simpson, a 38-year-old female, presented for biopsy and excision of a recently discovered lump in her right breast. Along with her routine preoperative blood work, her physician requested a blood test for CA 27.29. Subsequent requests for CA 27.29 levels were made for her two-week post-op follow-up visit and at one year and two years following her surgery. Results are shown in the table below. All testing was performed by the same laboratory, using the same immunoassay instrumentation and reagent systems. Reference interval for CA 27.29 using this test system is 0–40 U/mL.

Sample Result (U/mL)
Pre-op 602
2 weeks post-op 38
1 year post-op 41
2 years post-op 60

Issues and Questions to Consider

  1. Why did the values fall after surgery?
  2. Which value(s) indicate significant changes from the previous value?
  3. How would interpretation of these results be affected if the laboratory had changed instrument manufacturers during the time period represented?