Question

4a. A new test system to detect rheumatoid arthritis also reacts positively with the serum of up to 20% of patients with septic arthritis. This cross reactivity demonstrates the low of the test. (2) Is this test system a good one for confirming RA? or why not. (2) Explain why 4b.If the test exhibited very few false negatives what is being exhibited by the assay?(2) Explain why Is this test system a good one for screening for RA? or why not (2)

Answer 1

Answer: 4.a

As the new test to detect or diagnose the rheumatoid arthritis also reacted positively with the serum of up to 20 % of serum of the patients with septic arthritis. This cross reactivity demonstrates the low SPECIFICITY .

This test system is not good for confirming RA because in this test system 20% false positive are also detected. That means it can detect positive for the 20% of the people who are not having rheumatoid arthritis (RA). In another way we can say that the specificity of the test is only up to 80 %. Hence, it is having a test system with low specificity for the detection of RA.

4.b answer:

If the test exhibit very few negative it means the test is having high Sensitivity. Sensitivity refers to the ability of the test to detect the true positive cases.

As in this system of testing only few false negative cases are being detected this test system is a good system to detect or diagnose RA. Because this will able to detect all the positive cases and a few negative cases that can further be isolated via other methods and several other criteria for the confirmatory diagnosis of RA like EULAR.

Moreover this is a good method of detecting RA as it is having high sensitivity that the all RA positive can be detected easily.

Thank you