By Ana Sandoiu —– Updated on March 7, 2025
Medically Reviewed by: Jason Paul Chua, MD, PhD
In many if not most cases, neurologists can diagnose multiple sclerosis (MS) on the basis of symptoms, along with an MRI scan of the brain and spinal cord. But when results aren’t conclusive, they might turn to a spinal tap, also known as a lumbar puncture.
Read on to learn what a spinal tap entails, what it can and can’t reveal, and whether it poses any risks.
Spinal Tap Results and What They Mean
A spinal tap involves the removal of a sample of cerebrospinal fluid — the fluid that surrounds the brain and spinal cord.
A neurologist cannot 100 percent confirm or rule out MS by analyzing these fluids, says Barbara Giesser, MD, a multiple sclerosis specialist with Pacific Neuroscience Institute and a professor emeritus of clinical neurology at the David Geffen UCLA School of Medicine.
Even if spinal tap results are negative for MS, she notes, about 10 percent of people with MS have normal spinal fluid. “And other things [besides MS] can cause a positive result,” she says.
Despite these flaws, a spinal tap can be an important tool for MS diagnosis.
Researchers will analyze cerebrospinal fluid for the following:
- White Blood Cell Count White blood cells are part of your immune system. In MS, the total number of white blood cells is up to seven times higher than normal.[1] Levels of monocytes, basophils, and neutrophils (types of white blood cells) are also higher than normal.[3]
- Immunoglobulin G (IgG) Index Immunoglobulins are antibodies produced by plasma cells. [4] IgG is the most common type of immunoglobulin in the human body.
- [4] High IgG levels can signal MS or simply inflammation or trauma. So, to distinguish between the two, researchers calculate a so-called IgG index. A high IgG index can signal MS in about 90 percent of people with the condition.[5]
- Neurofilaments Neurofilaments and neurofilament proteins help create the structure that supports your neurons (nerve cells).[6] If fragments of these structures are in your spinal fluid, that could mean your myelin — the protein that covers and protects your neurons — has been damaged, as is the case in MS.[1][6]
- Oligoclonal Bands These are also called bands of immunoglobulins. When these are higher than normal, they signal a high level of inflammation in the body. This inflammation could result from damage to the myelin sheath, which would indicate MS.[7][1] About 85 percent of people with MS show oligoclonal bands in their spinal fluid.[2] Sometimes, testing does not reveal oligoclonal bands, especially in the early stages of the illness, but they appear later as the disease progresses.[2]
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