Laboratory or imaging test		Condition
Complete blood count
	Anemia	Many inflammatory arthritides, especially SLE, RA, IBD, and human parvovirus B19 infection
	Thrombocytopenia	SLE, human parvovirus B19 infection
	Thrombocytosis	Acute-phase reaction, vasculitis, infection
	Leukopenia	SLE, RA, Felty's syndrome, Sjögren's syndrome, human parvovirus B19 infection
	Leukocytosis	RA, vasculitis, reactive arthritis, infection
	Eosinophilia	SLE, RA, IBD, sarcoidosis, dermatomyositis, scleroderma, Churg-Strauss syndrome, PAN, eosinophilic fasciitis, cholesterol emboli
Chest radiograph
	Infiltrates or nodules	RA, sarcoidosis, Wegener's granulomatosis, Churg-Strauss syndrome
	Serositis	SLE, RA
	Upper lobe fibrosis	Ankylosing spondylitis
	Diffuse fibrosis	RA, scleroderma, polymyositis
Rheumatoid factor		Healthy persons; RA, SLE, Sjögren's syndrome, sarcoidosis, reactive arthritis, PMR, polymyositis, psoriatic arthritis, endocarditis, chronic infections, cancer, chronic liver disease, many nonrheumatic causes
Joint aspiration
	Culture	Infection
	Crystals	Gout, pseudogout
	White blood cell count	Inflammation: > 2,000 per mm3 (2 × 109 per L)
		Probable infection: > 50,000 per mm3 (50 × 109 per L)
Inflammatory markers: elevated erythrocyte sedimentation rate or C-reactive protein (CRP)		Infection, most inflammatory arthritides, advanced age, PMR, giant cell arteritis, cancer, anemia, pregnancy; menses
Antinuclear antibody		Healthy persons; SLE, RA, scleroderma, Sjögren's syndrome, vasculitis, polymyositis, medications, many nonrheumatic causes
Hepatic transaminase: elevated aspartate transaminase or alanine transaminase		SLE, PAN, sarcoidosis, hemochromatosis, Sjögren's syndrome, infectious hepatitis, polymyositis
Urinalysis
	Hematuria	SLE, Wegener's granulomatosis, PAN
	Proteinuria	SLE; Wegener's granulomatosis, amyloidosis
Elevated alkaline phosphatase		Bone metastases, Paget's disease, osteomalacia, PMR, ankylosing spondylitis, hyperparathyroidism
Electrocardiogram: atrioventricular block		Lyme disease, neonatal lupus, ankylosing spondylitis
Double-stranded DNA		SLE, especially lupus nephritis
Anti–SS-A (anti-Ro) and anti–SS-B (anti-La) antibodies		Sjögren's syndrome, SLE; healthy persons
HLA-B27		Healthy persons; spondyloarthropathies, reactive arthritis
Elevated uric acid		Gout, psoriatic arthritis, Paget's disease; healthy persons
False-positive VDRL		SLE, anticardiolipin antibody syndrome
Cytoplasmic antineutrophil cytoplasmic autoantibody (c-ANCA)		Wegener's granulomatosis
Elevated creatinine		SLE, Wegener's granulomatosis, vasculitis
Elevated creatine kinase (CPK)		Polymyositis, dermatomyositis, hypothyroidism
Elevated calcium		Hyperparathyroidism, cancer, sarcoidosis