Key Concept: Immunologic tests are not useful as screening tests

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Medscape

Introduction to Rheumatic Diseases

Key Concept/Objective: To understand that immunologic tests are not

useful as screening tests.

As a class, immunologic tests have low specificity and only moderate

sensitivity. They are more expensive than other clinical laboratory

tests, and the results are less reproducible. Immunologic tests should

never be used as screening tests; their greatest utility occurs when the

pretest probability of disease is high. The misuse of immunologic tests

frequently confounds the diagnosis and leads to unnecessary rheumatology

referrals. The use of so-called arthritis panels, in which many

serologic tests are bundled together, increases the likelihood of an

abnormal test result occurring in a patient without rheumatic disease;

such panels should be avoided. It is common for young women to test

positive for ANA; approximately 32% of young women will test positive

for ANA at low titers. A positive ANA in and of itself is by no means

diagnostic of systemic lupus erythematosus. The probability of testing

positive for rheumatoid factor increases with age even in healthy

persons. Additionally, conditions other than rheumatoid arthritis can be

associated with elevations in rheumatoid factor; because of this, a

positive test result for rheumatoid factor is not diagnostic of

rheumatoid arthritis. A careful and detailed history is the most

important part of the evaluation of a patient with arthritis. Laboratory

findings should be evaluated in the context of the information obtained

by a detailed history and physical examination. Diagnoses of rheumatic

diseases should not be based solely on the findings of immunologic

tests.

http://www.medscape.com/content/2003/00/46/35/463550/ans8.html

I'll tell you where to go!

Mayo Clinic in Rochester

http://www.mayoclinic.org/rochester

s Hopkins Medicine

http://www.hopkinsmedicine.org