A screening test for a rare disease has a likelihood ratio positive (LR+) of 8 and a likelihood ratio negative (LR−) of 0.1. Which statement best describes the clinical utility of this test?
A. The test is poor for ruling in the disease (low LR+) but excellent for ruling out the disease (high LR−)
B. The test has poor clinical utility for both ruling in and ruling out the disease
C. The test is excellent for ruling in the disease (high LR+) but poor for ruling out the disease (low LR−)
D. The test is excellent for both ruling in and ruling out the disease
Explanation
Understanding Likelihood Ratios (LR+ and LR−)
Key Point
Likelihood ratios quantify how much a test result changes the probability of disease. They are independent of prevalence and directly inform clinical decision-making.
LR− < 0.1: Strong evidence against disease (rules out)
LR− 0.1–0.2: Good-to-excellent evidence against disease
LR− 0.2–0.5: Moderate evidence against disease
LR− = 1: Test provides no diagnostic information
Analysis of This Test
Table
Metric
Value
Interpretation
LR+
8
Moderate-to-good evidence for ruling IN disease (5–10 range)
LR−
0.1
Good-to-excellent evidence for ruling OUT disease (≤ 0.1)
High-YieldNEET PG
An LR+ of 8 means a positive test increases the post-test odds of disease by a factor of 8 — this is considered moderate-to-good for ruling in disease. An LR− of 0.1 means a negative test decreases the post-test odds of disease by a factor of 10 — this is considered excellent for ruling out disease. Together, both values indicate a clinically useful test for both purposes.
Why Option A is wrong: Option A states the test is "poor for ruling out the disease," but an LR− of 0.1 is at the threshold of excellent for ruling out (the standard cutoff is ≤ 0.1). Calling it "poor" is factually incorrect.
Why Option C is correct: With LR+ = 8 (moderate-to-good for ruling in) and LR− = 0.1 (excellent for ruling out), the test demonstrates good clinical utility for both ruling in and ruling out disease. Per standard epidemiological thresholds (Park's Textbook of Preventive and Social Medicine; Sackett et al., Evidence-Based Medicine), both values fall in the clinically useful range.
Mnemonic
SnNOut / SpPIn
SnNout: High Sensitivity → Negative test result → rule Out disease
SpPIn: High Specificity → Positive test result → rule In disease
Clinical Pearl
A test with LR+ ≥ 5 and LR− ≤ 0.2 is generally considered useful for both ruling in and ruling out disease. This test meets both criteria, making Option C the best descriptor of its clinical utility (Park's Textbook of PSM, 26th edition; Sackett DL, Evidence-Based Medicine).
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