Lab tests in rheumatology Flashcards
What lab tests are used to assess acute phase response?
ESR and CRP
What do you measure with ESR
tendency of RBCs to sediment. depends on the ability of RBCs to aggregate under certain conditions- ESR incr. in proportion to the size of the RBC aggregates. ESR is affected by plasma proteins and the physical characteristics of the cells.
What do ESRs suggest? Why? limitations?
high ESR suggests inflammation. Inflammation causes incr. in acute phase reactants, which incr. the ESR. ESR can be elevated in conditions other than inflammatory rheumatic disease (MI, tissue damage).
pts age/2 (+10 for women) = normal ESR- so ESR incr. with age.
What is CRP
a protein that binds to many bacterial ligands. IT rises rapidly in inflammation and falls within days after inflammation subsides
again, non-specific
What are autoantibodies?
immunoglobulins directed against autologous intracellular, cell surface, or extracellular antigens. The presence of an autoantibody does not make a disease.
What is RF and how is it detected?
rheumatoid factor: this is an immunoglobulin against immunoglobuin- it binds to the Fc portion to IgG.
It is detected by latex agglutination: latex particles are coated with IgG. Put in pt’s serum. If there is RF, it will bind up the IgG molecules, and you can detect that. This can give a quantitative sense of the degree of autoantibodies.
What is the clinical utility of RF?
it is not very specific for rheumatoid arthritis (also commonly seen in Sjogren’s syndrome), though high titers are more suggestive of RA than low titers.
About 70% of RA pts have positive RF.
Less than 5% of normal ppl have RA (but many other conditions, including SLE, scleroderma, polymyositits chronic bacterial infections, and chronic inflammatory diseases also show elevated levels)
What is anti-CCP? sensitivity, specificity, disease
anti-cyclic citrullinated peptide newer autoantibody in RA that may be more relevant to pathogenesis- antibodies often develop before the disease is clinically evident. more specific (>96%) with slightly better sensitivity than RF (about 100% of RF pos pts are anti CCP pos; 40% of RF neg pts are anti-CCP pos).
Antinuclear antibodies
autoantibodies against intra-nuclear antigens
ANA advantages, specificity, sensitivity
the fluorescent ANA test is higly sensitive for SLE (>99%) but lower specificity (85%)
titter >1:80 is positive, and higher titers are more significant.
the pattern of ANA correlates with autoantigen specificity
How do you test for ANA
fluorescent anti-nuclear antibody test
add pts serum to test cells w big nuclei (cervical cells).
the ANA will bind to nuclear antigens.
wash, then incubate with fluorescein labeled anti-human IgG
look at under microscope
different patterns suggest different types of ANA
nucleolar binding is often seen in scleroderma
What ANA patterns might indicate SLE
diffuse, speckled, or rim//peripheral
what ANA patterns might indicate scleroderma?
nucleolar suggests diffuse scleroderma
centromere suggests limited scleroderma
Anti-dsDNA: clinical relevance, disease, sensitivity and specificity
highly specific for SLE but less sensitive (found in about 50%)
clinically associated with nephritis and titers correlate w/disease severity
Anti-smith
highly specific for SLE- but only found in about 30% of ppl w/SLE
antibodies against nuclear proteins involved in mRNA splicing (ribonucleorproteins)
