Laboratory Evaluations for Behçet's Syndrome
There is no specific diagnostic laboratory test for Behçet's syndrome; diagnosis remains clinical, but laboratory evaluations serve to exclude alternative diagnoses, assess inflammatory activity, and evaluate organ involvement. 1
Essential Laboratory Tests
Basic Inflammatory and Hematologic Markers
- Complete blood count (CBC) to assess for leukocytosis, thrombocytosis, or anemia that may indicate active inflammation 2, 3
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are elevated during active disease and useful for monitoring disease activity 4
- Systemic Immune-Inflammation Index (SII) calculated as neutrophils × platelets/lymphocytes may be helpful, with values >552 × 10³/mm³ suggesting active disease with 81% sensitivity and 82% specificity 4
Organ-Specific Evaluations Based on Clinical Presentation
For gastrointestinal involvement:
- Endoscopy and/or imaging to confirm gastrointestinal involvement 1
- Rule out NSAID ulcers, inflammatory bowel disease, and tuberculosis infection 1
For vascular involvement (deep vein thrombosis):
- Imaging studies (ultrasound, CT, or MRI) to document thrombosis 1
- Important caveat: Anticoagulation studies are generally not indicated as thrombosis in Behçet's results from vessel wall inflammation rather than hypercoagulability 1
For neurological involvement:
- Cerebrospinal fluid (CSF) examination showing elevated protein with normal cell count (albumino-cytological dissociation pattern) 5
- Brain MRI to identify parenchymal lesions, particularly at the meso-diencephalic junction, ponto-bulbar regions, thalamus, or basal ganglia 5
- Screen for extracranial vascular disease when cerebral venous thrombosis is present 1
For ocular involvement:
- Close ophthalmologic collaboration is essential; laboratory tests primarily exclude infectious causes 1
Tests to Exclude Alternative Diagnoses
- Serum electrolytes, renal function, and liver function tests to exclude other systemic conditions 2
- Infectious disease screening including tuberculosis testing when gastrointestinal or systemic symptoms are present 1
- Autoimmune serologies may be considered to exclude other rheumatologic conditions, though these are typically negative in Behçet's 2
Pathergy Test
- Skin pathergy test remains diagnostically valuable, though sensitivity has decreased over time 2, 3
- Positive pathergy test (pustule formation 24-48 hours after needle prick) supports diagnosis but is not required 2
- Pathergy test positivity was 39.9% in a recent cohort of 777 patients 3
HLA Testing
- HLA-B51 testing may provide supportive evidence, as it shows high prevalence in Behçet's patients, particularly along the ancient Silk Road distribution 2
- However, HLA-B51 is neither sensitive nor specific enough to be diagnostic on its own 2
Important Diagnostic Considerations
Critical pitfall: Do not delay treatment waiting for confirmatory laboratory results, as Behçet's diagnosis is primarily clinical based on the International Study Group criteria (recurrent oral ulcers plus two of: recurrent genital ulcers, eye lesions, skin lesions, or positive pathergy test) 2
Heterogeneity alert: Different clinical subsets (mucocutaneous-only, ocular, vascular) display distinct molecular expression profiles and may represent a syndrome rather than a single disease entity 6. Laboratory abnormalities may vary significantly between these subsets 6
Gender and severity: Male patients, particularly young men, tend to have more severe disease with major organ involvement (ocular, cardiovascular, neurologic), which should guide the intensity of laboratory monitoring 3