Diagnostic Rheumatologic Evaluations Flashcards
Sensitivity
If the test is highly sensitive and the test result is negative you can be nearly certain that they don’t have disease. Sensitive test helps RULE OUT disease when the result is negative. Sensitivity - rule out or “Snout”
Specificity
If the test result for a highly specific test is positive you can be nearly certain that they actually have the disease. A very specific test RULES IN disease with a high degree of confidence. Specificity - rule in or “Spin”
Acute Phase Reactants
- ESR (erythrocyte sedimentation rate);
- CRP (c-reactive protein);
- Platelets and ferritin are other acute phase reactants
ESR
Rate RBC sediment 1 hour. Anticoagulated blood placed in an upright tube, Westergren tube, and the rate at which the RBCs fall is measured and reported in mm/h.
The red cells form stacks called ______ which settle faster
Rouleaux
What can increase ESR?
Increases in: Infection, Malignancy, Connective tissue disorders ………. Non-inflammatory conditions causing elevation include: Advancing age, Female sex, Obesity, Pregnancy, Anemia.
Estimating ESR: Rule of Thumb
ESR < age in years (+ 10 if female) / 2; Normal ESR does NOT exclude inflammatory condition
What triggers CRP?
Inflammatory conditions cause release of interleukin-6 and other cytokines that trigger the synthesis of CRP and fibrinogen by the liver. During the acute phase response, levels of CRP rapidly increase within 2 hours of acute insult. Reaches peak at 48 hours.
Role of CRP
Physiological role is to bind to phosphocholine expressed on the surface of dead or dying cells (and some types of bacteria) in order to activate the complement system. ……….. Shorter half-life than ESR. With resolution of the acute phase response, CRP declines with a relatively short half-life, 18 hours.
What causes an increase in CRP?
Acute & chronic inflammatory conditions: Bacterial, viral, or fungal infections; Rheumatologic, Malignancy, Tissue injury or necrosis.
How do we use older CRP tests?
The older tests for CRP is adequate for monitoring severe inflammatory conditions. Older test does not have the ability to measure levels accurately within the range needed for cardiac risk detection.
When to order ESR/CRP?
Concern that there is inflammatory process and to help document degree of inflammation ……………Inflammatory arthritis such as RA, Polymyalgia Rheumatica, Vasculits. Typically not elevated in seronegative spondylarthropathies
Anti-Nuclear Antibody (ANA)
Autoantibodies that bind to contents of the cell nucleus. In normal individuals, the immune system produces antibodies to foreign proteins (antigens) but not to human proteins (autoantigens). Patterns of fluorescence visually represent the distribution of antibodies to specific types of nuclear antigens.
Positive ANA Tests
A positive test is identified arbitrarily as the level of ANA exceeding that seen in 95% of normal individuals. + varies with lab, typically 1:80 or 1:160. + titer < 1:160 are present in up to 20% of the healthy population, especially the elderly. + titer > 1:160 found in 5% of healthy individuals
Types of ANA Reuslts
Homogenous: Lupus, drug induced lupus ………. Speckled: Lupus, scleroderma, Sjogren’s ……… Nucleolar: scleroderma, polymyositis ……… Centromere: limited scleroderma (CREST)
Significance of +ANA
Depends on clinical context. Should be used as a confirmatory test when an autoimmune disease is strongly suspected clinically. ANA does not confirm a diagnosis of SLE. Lack of ANA makes SLE unlikely. Variations in ANA titers do not correlate with disease activity in autoimmune diseases.
Associated + ANA
Medications (procainamide, hydralazine, INH), Hepatic, diseases, Endocrine disorders – THYROID disease!
Renal failure, Healthy individuals, Normal elderly >70, SLE, Rheumatoid arthritis, Scleroderma, Sjogrens syndrome, Myositis
Anti-Cytoplasmic Antibody (ANCA)
Antibodies directed against components of granules present in the cytoplasm of neutrophils. ANCA strongly associated with systemic vascultis.
