What laboratory tests should be ordered to evaluate a possible multiple sclerosis relapse?

Blood Tests for MS Attack

When evaluating a possible MS relapse, blood tests are primarily used to exclude alternative diagnoses (mimics and pseudoattacks), not to confirm the relapse itself—the diagnosis of an MS attack remains fundamentally clinical, requiring objective neurological signs lasting at least 24 hours. 1

Core Principle: MS Relapse is a Clinical Diagnosis

An MS attack requires objective clinical findings on examination, not laboratory confirmation 1. Blood work serves to rule out conditions that can mimic relapses, such as:

• Infection (which can trigger pseudoattacks through temperature elevation)
• Metabolic disturbances
• Alternative autoimmune/inflammatory conditions

Recommended Laboratory Approach

Essential Exclusionary Testing

Based on current practice patterns and diagnostic algorithms 2, 3, 4, the following serum tests are most commonly ordered:

Infection screening:

• Complete blood count with differential
• C-reactive protein or erythrocyte sedimentation rate (ESR)
• Urinalysis (to exclude urinary tract infection as pseudoattack trigger)

Metabolic/endocrine:

• Thyroid stimulating hormone (TSH) - ordered by 31.6% of neurologists "always" 2
• Comprehensive metabolic panel

Autoimmune screening (when clinical red flags present):

• Antinuclear antibody (ANA) - ordered by 43.2% "always" 2
• Consider aquaporin-4 (AQP4) antibodies and myelin oligodendrocyte glycoprotein (MOG) antibodies if atypical features suggest NMOSD or MOGAD 5, 4, 6

Important Caveats

Avoid over-testing: Recent surveys show neurologists order an average of 17.2 tests when evaluating possible MS 2. However, many of these tests have poor specificity and can lead to false positives, diagnostic delay, and misdiagnosis 2. Focus testing based on clinical red flags rather than ordering extensive panels reflexively.

CSF analysis is NOT routinely needed for relapse confirmation 1, 3. CSF oligoclonal bands and IgG index are diagnostic tools for establishing the initial MS diagnosis, not for confirming individual relapses. CSF may be considered if:

• The clinical presentation is atypical
• Alternative diagnoses need exclusion
• This represents a first demyelinating event requiring diagnostic confirmation

Clinical Algorithm for Relapse Evaluation

1. Confirm true relapse clinically:

   • Objective neurological signs on examination
   • Duration ≥24 hours
   • Exclude pseudoattack (fever, infection, heat exposure)

2. Order targeted blood work:

   • CBC, CRP/ESR, urinalysis (exclude infection)
   • TSH, metabolic panel (exclude metabolic triggers)
   • ANA only if atypical features present

3. Consider MRI with gadolinium (not blood test, but critical):

   • Demonstrates active inflammation
   • More sensitive and specific than laboratory tests 1

4. Reserve specialized antibody testing (AQP4, MOG) for atypical presentations suggesting MS mimics 5, 4

Key Pitfall to Avoid

Do not delay treatment waiting for blood test results if clinical relapse is clear. The evidence supports that objective clinical examination is sufficient to diagnose a relapse 1, 3. Blood tests should run concurrently with clinical decision-making, not gate treatment initiation.