Rheumatology Workup - Laboratories Studies in Rheumatic Diseases • Septic arthritis - Gram stain and culture of synovial fluid • Gout or pseudogout - Compensated polarized light microscopy to examine a drop of synovial fluid for intracellular urate crystals (gout) or calcium pyrophosphate dihydrate crystals (pseudogout) • Ankylosing spondylitis - Sacroiliac joint radiography to demonstrate bilateral sacroiliitis • Osteoarthritis - Radiography of the affected joint • Systemic lupus erythematosus (SLE) - Antinuclear antibody (ANA) test; if positive, test for Smith (Sm) and double-stranded DNA antibodies, which are more specific for SLE but present in only 30% and 60% of SLE patients, respectively Screening Tests for All Types of Inflammatory Arthritis: • Erythrocyte sedimentation rate (ESR) • C-reactive protein (CRP) • Rheumatoid factor (RF) and cyclic citrullinated peptide (CCP) antibody • ANAs RF test should be obtained when rheumatoid arthritis (RA) is considered at least moderately possible. - Positive in as many as 20% of healthy elderly persons - CCP antibody testing has higher specificity than the RF test but lower sensitivity - >95% of patients with SLE have ANAs; thus, a negative ANA result is a strong indicator that SLE is not present. CRP Level: • A nonspecific measure of inflammation and is obtained as an alternative to obtaining the ESR. • In contrast to the ESR, the CRP level: (1) Can be measured on frozen serum (2) Is not influenced by the presence of anemia or hyperglobulinemia (3) Rises more rapidly in response to an inflammatory stimulus, and (4) may require more time for the laboratory result to be available (i.e., more than 24 hours, as opposed to 1 hour for the ESR). Screening Tests for Acute Polyarthritis: • Blood cultures • Antistreptolysin O titer • Parvovirus B-19 immunoglobulin G (IgG) and immunoglobulin M (IgM) levels • Hepatitis B serology • ANAs • Additional tests: HIV test, a rubella titer, ACE level, CXR, ANCA test Screening Tests for Chronic Polyarthritis: • Complete blood count (CBC) • ESR and CRP level • ANAs • RF and CCP antibody • Chemistry profile, including liver function tests (LFTs) and a serum creatinine level • Serum uric acid level • Urinalysis • Others – to consider: TSH level, serum ferritin level, and iron saturation of serum transferrin Screening Tests for Diffuse Arthralgias and Myalgias: • ESR and CRP level to exclude inflammatory disease (e.g., polymyalgia rheumatica) • Creatine kinase and aldolase level to exclude myositis • Thyroid testing • Chemistry profile (e.g., calcium, phosphorus, electrolyte, glucose, and total protein) to exclude metabolic or endocrine disorders Additional Tests for Diffuse Arthralgias and Myalgias: • 25-hydroxy vitamin D level (in elderly housebound individuals, to exclude osteomalacia) • Sacroiliac joint radiography (to exclude ankylosing spondylitis, especially in women younger than 45 years with neck, chest wall, and low back pain) • HLA-B27 (to support a diagnosis of reactive arthritis) • Hepatitis B and C serology testing • Serum and urine protein electrophoresis (to exclude multiple myeloma) • ANA and RF (if clinical features suggest RA, SLE, or another connective-tissue disease) #Rheumatic #Disease #Rheumatoid #Arthritis #laboratory #workup #diagnosis #testing #Rheumatology
