There is currently no single, definitive test that allows doctors to diagnose multiple sclerosis (MS). This means that doctors must rule out other similar diagnoses through a process of elimination. Neurologists (doctors specializing in disorders of the nervous system) may use blood tests, MRI, or lumbar puncture (also called a spinal tap) to help diagnose MS or rule out conditions that resemble it.

MS is a disease of the central nervous system (CNS), which includes the brain and spinal cord. MS is caused by an abnormal immune system response that attacks myelin, the fatty tissue that insulates nerves. The loss of myelin can lead to disrupted communication between the brain and the body. MS can cause a wide range of symptoms, which vary depending on how severe an individual case is: Some people with MS are unable to walk, for example, while others have minimal effects.

Although there is no cure for MS, many treatments exist that can manage its symptoms, slow its progression, and help people recover from attacks. But before a person’s MS can be treated, they need an accurate diagnosis.

Using Blood Tests To Rule Out Other Conditions

Many blood tests can help doctors rule out other conditions during the diagnostic process, helping to pinpoint a diagnosis of MS.

B12 and Folate Tests

Some of the most common symptoms of MS include weakness, fatigue, dizziness, tingling in the feet and hands, and forgetfulness or mental changes. Many of these overlap with the symptoms of anemia caused by vitamin deficiency (low levels of B12 or folate). Testing for these vitamins in the blood can help rule out vitamin-deficiency anemia as the cause of MS-like symptoms.

Antinuclear Antibody, Erythrocyte Sedimentation Rate, and Rheumatoid Factor Tests

Symptoms like fatigue and pain are common in people with lupus and rheumatoid arthritis. Antinuclear antibody, erythrocyte sedimentation rate, and rheumatoid factor blood tests help detect these particular disorders.

Many MyMSTeam members also have similar symptoms, so these blood tests can help doctors determine which condition or conditions are present.

Lyme Disease, HIV, and HTL-1 Tests

When diagnosing MS, doctors use blood tests to rule out certain infections. This includes Lyme disease, human immunodeficiency virus (HIV), and human T-lymphotropic virus cell type 1 (HTLV-1).

Symptoms of Lyme disease may include aching muscles and joints, while HIV symptoms that overlap with those of MS include body pain and fatigue. HTLV-1 can cause tingling of the hands and feet, sexual dysfunction, and abnormal reflexes, which can all be seen in MS.

Anticardiolipin Antibody Tests

Antiphospholipid antibody syndrome is another condition that can resemble MS (as well as lupus). This disease can cause abnormal blood clotting, along with headaches, weakness, vision changes, and speech changes that can mimic MS symptoms. A blood test called anticardiolipin antibody test can help confirm antiphospholipid antibody syndrome, and a negative test can point toward another disease, like MS.

Angiotensin-Converting Enzyme Tests

Angiotensin-converting enzyme (or ACE) tests measure the level of this particular enzyme in the blood. High levels can indicate sarcoidosis, an inflammatory condition that can cause fatigue, headaches, and soreness or stiffness of the joints, all common MS symptoms.

Testing Before Starting Disease-Modifying Treatments

Before prescribing a disease-modifying treatment (DMT), doctors typically conduct blood tests to see which medicines are safe. For example, your health care team will probably order blood tests before prescribing certain medications that reduce the immune system’s activity against the CNS. These blood tests are important because people taking these types of drugs can be at risk of certain infections as well as blood cell level abnormalities.

For example, ozanimod (sold as Zeposia) can lower lymphocyte (white blood cell) counts and increase your risk for infections, some of which can be fatal. Therefore, blood cell counts are monitored before therapy.

These medications can also affect liver function, so doctors will check liver enzyme levels in the blood before you take them.

Alemtuzumab (Lemtrada) can affect kidney function, and ocrelizumab (Ocrevus) has been known to reactivate the hepatitis B virus in those who’ve been infected. Blood tests can be done to look for both of these issues before treatment begins.

Finally, doctors considering using formulations of natalizumab (such as Tysabri) should perform a blood test to detect John Cunningham virus (JCV). People with weakened immune systems who carry JCV are at increased risk of a rare brain infection that can result in progressive multifocal leukoencephalopathy, which is often fatal.

Monitoring During MS Treatment

Once you and your doctor have chosen a DMT, you may need to continue undergoing blood tests to keep tabs on any side effects. For example, interferon beta medications — including Avonex, Betaseron, Extavia, Plegridy, and Rebif — have been known to cause liver damage, so ongoing blood tests are necessary to monitor liver enzymes.

The majority of disease-modifying therapies for MS also require regular, ongoing complete blood count (or CBC) tests, which monitor white blood cells, red blood cells, hemoglobin, hematocrit, and platelets. Abnormalities in these levels can lead to blood clotting, abnormal bleeding, infections, anemia, and more, so it’s important to ensure they’re within healthy limits.

Will Blood Tests Diagnose MS in the Future?

No two people with MS are the same, but there’s reason to be optimistic that diagnostic blood tests may be quicker and more conclusive in the future. For instance, research into biomarkers may hold a great deal of promise. Biomarkers are biological molecules found in a person’s bodily fluids (including blood) and tissues that can point to particular health conditions.

Medical technology company Numares is developing a blood test that differentiates between progressive and relapsing forms of MS, thereby shedding light on whether a particular treatment is working. University College London’s Dr. Sharmilee Gnanapavan is comparing markers of nerve damage from MS in people taking alemtuzumab and ocrelizumab.

Finally, a team of researchers at the University of Huddersfield found that MS may be detectable in the breath. With additional research and testing, this could mean that a simple breath test may one day take much of the guesswork out of the diagnostic process.

The use of biomarkers to diagnose MS shows promise, particularly when combined with imaging studies and other evaluation tools.

Talk With Others Who Understand

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 192,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Have questions about blood tests? Do you get nervous before getting your blood drawn? Comment below or start a new conversation on MyMSTeam.