Clinical Context
This question tests the application of screening test results in clinical decision-making — a high-yield concept in NEET PG biostatistics and preventive medicine.
Understanding the Positive FIT Result
Key Point
A positive faecal immunochemical test (FIT) in a colorectal cancer screening programme is an indication for colonoscopy — the gold standard for definitive diagnosis. This is the established clinical pathway per national and international guidelines (USPSTF, Indian guidelines for colorectal cancer screening).
Calculating Positive Predictive Value (for context)
Using Bayes' theorem with Sensitivity = 0.92, Specificity = 0.87, Pretest probability = 0.03:
PPV=(0.92×0.03)+(0.13×0.97)0.92×0.03=0.15370.0276≈18%
High-YieldNEET PG
Even though the PPV is only ~18%, this represents a 6-fold increase over the baseline 3% pretest probability. The positive likelihood ratio (LR+) = 0.92 / 0.13 ≈ 7.1, which is moderately strong evidence for disease.
Why Colonoscopy is the Most Appropriate Next Step
In the "best next step in management" framework:
- 1.
Colonoscopy is the established next step after a positive FIT in any screening programme — this is guideline-driven clinical action (Harrison's Principles of Internal Medicine, 21st ed.)
- 2.
Calculating PPV is a background statistical exercise that informs counselling, but it is NOT itself a "management step" — it does not change the clinical pathway
- 3.
A positive FIT mandates colonoscopy regardless of the exact PPV calculation, because the post-test probability (18%) is substantially above the pre-test probability (3%)
- 4.
Reassurance and repeat FIT (Option A) would be inappropriate — a positive result must be investigated
- 5.
Referral for chemotherapy (Option D) is premature without histological diagnosis
Why Option C is Incorrect as the "Best Next Step"
Clinical Pearl
While counselling on PPV is good practice and should accompany the referral, it is not the most appropriate next step in management. The actionable clinical decision is to proceed to colonoscopy. Framing "calculate PPV" as the primary next step conflates a statistical exercise with a management action.
Management Algorithm
| Step | Action |
|---|
| 1 | Positive FIT result |
| 2 | Counsel patient (including PPV context) |
| 3 | Proceed to colonoscopy ← Most appropriate next step |
| 4 | Definitive diagnosis ± treatment |
Key Point
Per Harrison's and standard screening guidelines, a positive FIT → colonoscopy is the correct clinical pathway. The "best next step" is colonoscopy (Option B).
