Biostatistics & Research · patient case question
What is a FALSE POSITIVE result?
Patient case: Evidence, and a Patient Irradiated Ten Years Ago
Patient: 66-year-old male
Chief Complaint: Two non-restorable mandibular molars requiring extraction.
Background: Squamous cell carcinoma of the floor of mouth treated ten years ago with surgery and RADIOTHERAPY to the head and neck, total dose approximately 66 Gy. Currently disease-free. His new dentist is reviewing the published evidence on managing extractions in irradiated bone.
Medications: None
Vital Signs: BP 132/80 mmHg · HR 74 bpm · RR 16 · T 98.4°F
Findings: Teeth #30 and #31 are non-restorable with periapical radiolucencies. Overlying mucosa is intact. Xerostomia with rampant cervical caries on the remaining dentition. Trismus with maximum opening 32 mm.
Show answer and explanation
Correct answer: B. The test indicates disease is present when the patient does not actually have it
- A. That describes a TRUE NEGATIVE.
- B. CORRECT. A FALSE POSITIVE is a positive test result in a person who does NOT have the condition. Its consequences are unnecessary anxiety, further investigation, and sometimes unnecessary treatment — a false positive on a caries-detection device leads to a restoration in sound enamel.
- C. That describes a TRUE POSITIVE.
- D. That describes a FALSE NEGATIVE — the more dangerous error in most clinical settings, because disease goes undetected and untreated.
Note: The formulas, which are worth writing out rather than memorising as strings: SENSITIVITY = TP / (TP + FN) — the proportion of DISEASED people the test correctly identifies, so a sensitive test rules disease OUT when negative (SnNout). SPECIFICITY = TN / (TN + FP) — the proportion of HEALTHY people correctly identified, so a specific test rules disease IN when positive (SpPin). ⚑ Sensitivity is TP/(TP+FN), NOT TN/(TN+FN) — that miswriting circulates in several files in this series.
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