Serology and Lab Testing (Johnston) Flashcards
What does the diagnosis of RA depend on?
history and physical exam; no single test is diagnostic (but supportive)
What are the two markers of inflammation in RA?
ESR - good marker for chronic inflammatory disorders
CRP - more sensitive and good for assessment of disease activity
ESR markers
marker of inflammation; rises with age and higher in women; non specific indicator of inflammation; good marker for chronic inflammatory disorders
CRP
non specific mark of inflammation; assess disease activity; synthesized in the liver; can activate complement and promote phagocytosis; >8mg/L is inflammation; more sensitive than ESR and rises and falls quicker
Why is ESR a better marker for chronic inflammatory conditions than CRP
CRP is an acute phase reactant that rises and falls quicker than ESR
Why should serologies never be used as the sole criteria for RA diagnosis?
limitations in sensitivity ad specificity (too much variation)
Rheumatoid Factor (RF)
IgM antibody that targets the Fc portion of IgG; produced by B cells in synovial joints; present in 70% of RA patients and 100% in nodular RA
Rheumatoid Factor (RF) is a confirmatory test for which pathology?
nodular RA; found in 100% of patients
What is the most common type of Rheumatoid Factor (RF)?
IgM (but can be any subclass)
What percent of healthy patients will have a false positive with Rheumatoid Factor (RF) testing?
1-4% and in 20% patients >60 yrs
What percentage of RA patients are RF negative?
20-30%
Anti-CCP
antibodies to citrullinated proteins; present in 70% of early RA patients; more specificity than RF in RA patients
A patient that is CCP plus RF positive has what specificity of having RA?
99.5% specificity for RA
Homogenous pattern of ANA on immunofluorescence should make you suspect what disorder?
lupus; if histone antibody than >95% chance of drug induced lupus
Rim pattern of ANA on immunofluorescence should make you suspect what disorder?
SLE (anti-dsDNA)
Speckled pattern of ANA on immunofluorescence should make you suspect what disorder?
anti-SM (smith) = lupus
anti- SS-A/SS-B = Sjogren syndrome
Characteristic of SLE
malar rash; discord rash; photosensitivity; oral ulcers; arthritis; and serositis