What is the effect of a positive test result with a high LR+?

What is the effect of a positive test result with a high LR+?

• A. Strong evidence for disease
• B. No information
• C. Decreases probability of disease
• D. Confirms only when prevalence is high

Answer: (A)

A positive test result with a high LR+ provides strong evidence that the disease is present. The likelihood ratio for a positive result (LR+) tells you how much more likely a positive test is in someone with the disease than in someone without it. When LR+ is high, a positive result markedly increases the odds that the patient has the disease, effectively moving the patient’s probability from a pre-test estimate to a much higher post-test probability. For example, if your pre-test probability is moderate, a high LR+ can push the post-test probability well into a range where you would reasonably diagnose the disease. The exact shift depends on the starting pre-test probability, because post-test odds = pre-test odds × LR+. But the key idea is that a high LR+ makes a positive result very informative for confirming disease, more than a low LR+ would. The other options don’t fit because a positive result with a high LR+ is not no information, nor does it usually decrease the disease probability, and it isn’t something that only applies when prevalence is high. The main point is that a high LR+ means strong diagnostic evidence toward the disease.

A positive test result with a high LR+ provides strong evidence that the disease is present. The likelihood ratio for a positive result (LR+) tells you how much more likely a positive test is in someone with the disease than in someone without it. When LR+ is high, a positive result markedly increases the odds that the patient has the disease, effectively moving the patient’s probability from a pre-test estimate to a much higher post-test probability.

For example, if your pre-test probability is moderate, a high LR+ can push the post-test probability well into a range where you would reasonably diagnose the disease. The exact shift depends on the starting pre-test probability, because post-test odds = pre-test odds × LR+. But the key idea is that a high LR+ makes a positive result very informative for confirming disease, more than a low LR+ would.

The other options don’t fit because a positive result with a high LR+ is not no information, nor does it usually decrease the disease probability, and it isn’t something that only applies when prevalence is high. The main point is that a high LR+ means strong diagnostic evidence toward the disease.