Multiple Sclerosis (MS)

Tests used in MS diagnosis

Why blood tests can't diagnose MS

Types of MS

Questions to ask your neurologist

• Do I meet the McDonald criteria for MS?
• Have AQP4 and MOG antibodies been checked?
• Which disease-modifying therapy is right for my type of MS?
• How often should I have MRI monitoring?

Frequently Asked Questions

Why MS has no single confirmatory blood test

There is no blood test that diagnoses multiple sclerosis. Diagnosis rests on the McDonald criteria, which require evidence of damage occurring in more than one part of the central nervous system and at more than one point in time, established by clinical episodes together with MRI findings and, where needed, oligoclonal bands in cerebrospinal fluid. Blood tests are ordered for the opposite purpose: to exclude conditions that imitate MS on scans or symptoms, including vitamin B12 deficiency, lupus, Sjögren's syndrome, sarcoidosis, Lyme disease, syphilis and neuromyelitis optica, the last of which is distinguished by testing for aquaporin-4 antibodies and is treated quite differently.

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

1. Multiple Sclerosis. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK499849

References

Sources cited on this page. PubMed links open the original abstract.

1. Compston A, Coles A. Multiple sclerosis. Lancet. 2008;372(9648):1502–1517. PMID 18940887 · doi:10.1016/S0140-6736(08)61620-7

How MS is diagnosed – the McDonald criteria

Multiple sclerosis is diagnosed using the McDonald criteria (revised 2017), which establish "dissemination in space" (lesions in at least two different parts of the CNS) and "dissemination in time" (evidence of at least two separate attacks or ongoing disease activity). Key diagnostic investigations:

• MRI brain and spinal cord: The cornerstone investigation. MS lesions (plaques) are white matter lesions with characteristic locations: periventricular, cortical/juxtacortical, infratentorial (brainstem/cerebellum), and spinal cord. Active lesions enhance with gadolinium contrast (indicating acute inflammation with blood-brain barrier breakdown). The number, location, and enhancement status of lesions determines whether McDonald criteria are met and guides prognosis (lesion burden correlates with long-term disability).
• CSF analysis (lumbar puncture): Oligoclonal bands (OCBs) – antibody fragments present in CSF but absent from serum – are found in approximately 90–95% of MS patients. OCBs are a marker of intrathecal immunoglobulin production and support the diagnosis when MRI criteria are not fully met. A raised IgG index and pleocytosis (mild lymphocyte increase) are also typical but less specific.
• Visual evoked potentials (VEPs): Slow or absent VEP responses indicate demyelination in the optic nerve – supporting dissemination in space even when optic neuritis was asymptomatic or occurred years before presentation.

Blood tests in MS – what they rule out, not rule in

There is no blood test that diagnoses MS. Blood tests are used to exclude conditions that mimic MS:

• AQP4-IgG (aquaporin-4 antibody): The most important MS mimic – neuromyelitis optica spectrum disorder (NMOSD). Severe optic neuritis and transverse myelitis in NMOSD are distinguished from MS by this antibody, which is present in 70–80% of NMOSD patients and absent in MS. NMOSD is treated differently – rituximab, eculizumab – not with standard MS therapies, which can paradoxically worsen NMOSD.
• MOG-IgG (myelin oligodendrocyte glycoprotein antibody): Another MS mimic – MOG antibody disease (MOGAD). Associated with optic neuritis, ADEM (acute disseminated encephalomyelitis), and cortical encephalitis. Responds better to steroids than MS treatments.
• B12, HIV, syphilis VDRL, Lyme serology: Infectious and nutritional causes of spinal cord disease (subacute combined degeneration, HIV myelopathy, syphilitic myelitis, Lyme neuroborreliosis) that can present with MS-like symptoms.
• ANA, anti-dsDNA, ANCA: SLE and vasculitis can cause white matter lesions and neurological events mimicking MS – particularly in younger women.