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
What immunologic cause can present with a false positive RPR?
syphilis
Antistrptolysin O antibody (ASO tidier) is found to be elevated following which type of infection?
group A streptococcal infection; may cause post-streptococcus reactive arthritis
What is level of uric acid is considered to elevated?
uric acid > 6.8 mg/dl
Characteristic of uric acid crystals
needle-shaped with a negative birefringent by polarized light microscopy
Characteristics of gouty arthritis
acute onset; monoarticular; often 1st MTP joint (podagra - hot, swollen, tender, dusky and red); presents often with nocturnal awakening; attacks knees, feet and ankles; tophi present; most common in men (90%) and in postmenopausal women
effects of alcohol on gouty arthritis?
alcohol promotes increased rate production and decreases excretion
tophi
nodular deposits of monosodium rate crystals in skin; often seen in gouty arthritis
A 46‐year‐old male presents with fatigue, malaise, pain in both wrists and bilateral swelling over MCP joints. He admits to previous history of lupus. The symptoms have been present for past 6 weeks. Physical exam reveals decreased strength in both hands, swollen wrists, PIPs and MCP joints bilaterally, and a nodule on the extensor surface of the left arm.
Which laboratory tests would you expect to be abnormal in this
case?
A. CBC indicating hemolytic anemia, leukocytosis and a negative RPR
B. Low complement (C3), decreased ferritin and elevated platelet
count
C. Positive anti‐CCP, elevated ESR and elevated rheumatoid factor
level
D. Positive ANA, negative rheumatoid factor and elevated CRP
E. Thrombocytosis, hypocalcemia and normal ESR
C. Positive anti‐CCP, elevated ESR and elevated rheumatoid factor level
Presence of a positive anti CCP plus a positive RF correlates to 99.5% specificity for RA. RF is positive 100% with nodules in RA patient.
gouty arthritis involving the 1st MTP joint (podagra - hot, swollen, tender, dusky and red)
severe tophaceous gout with large tophi and joint destruction in the hands
Chronic management for gouty arthritis?
xanthine oxidase inhibitor or probenecid (blocks tubular resorption of urate and increases uric acid excretion)
Treatment for acute gout?
NSAIDs (pain relief)
Colchine (watch for GI toxicity)
Steroids (decrease inflammation, not chronic treatment)
Radiography
poor visualization of soft tissues; can show RA symmetrical involvement of MCP; decreased bone loss with osteopenia and erosions; but plain radiographs may not detect early erosive arthritis disease
Ultrasonography (US)
sensitive imaging for soft tissue abnormalities and erosions; can also aid in injecting and aspirating joints
What imaging is ideal for soft tissue imaging and can aid in injecting and aspirating joints?
Ultrasonography (US)
MRI
gold standard for soft tissue abnormalities; good for spine imaging as well; but is expensive and cannot do at the bedside; contrast is contraindicated in patients with kidney disease
CT
best for bony abnormalities, erosions, fractures and inflammatory arthritis; more sensitive than MRI for bone erosions
What is the best imaging for bony abnormalities?
CT
A 50‐year‐old carpenter presents with pain, swelling and decreased range of motion in the right elbow (he is right side dominant). The elbow is swollen and very tender to touch. He relates to doing a lot of hammering, lifting boards and sawing.
Which imaging study is indicated in the evaluation of the patient’s complaint?
A. CT of right arm – attention elbow
B. Plain radiography (x‐rays) of elbow
C. MRI right arm – attention elbow
D. Ultrasonography – attention right elbow
E. Bone scan – attention right elbow
D. Ultrasonography – attention right elbow
Ultrasound is sensitive for soft tissue abnormalities, soft tissue swelling, synovitis, tendonitis, bursitis. Aid in aspirating or injecting joint
common joints affected in RA patients; look for symmetry and wrist, knees and ankles
common joints affected in OA; cervical and lumbar spine; knees and big toe
cardinal features of inflammation?
pain, swelling, redness, heat and tenderness
symmetrical polyarthritis of the wrist; RA
acute monoarthritis in gouty arthritis; podagra
Swan Neck deformity seen in RA; hyperextension
Boutonniere deformity seen in RA; hyperflexion
bony deformity of the DIP and PIP joints seen in OA; best imaging is CT
