How Measles Is Diagnosed

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Measles, also known as rubeola, is diagnosed by your symptoms, particularly fever, spots in your mouth, and the measles rash, as well as blood tests to confirm that you have measles and not one of several other conditions that can mimic some of its signs and symptoms, such as scarlet fever or mono.

Nearly 246 people worldwide, usually children, die per day from this preventable disease.

Measles-related deaths most frequently occur in developing countries with poor healthcare systems, but there are more and more outbreaks of measles in the United States and Europe due to lowered vaccination rates.

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If you or your child have developed the symptoms of measles, particularly a high fever with the measles rash and bright red spots with white centers in your mouth (Koplik's spots), it's probably safe to say that you have measles. If you or your child are unvaccinated and have been exposed to someone with measles or traveled internationally, measles is even more likely.

Although many childhood illnesses are accompanied by a rash, the measles rash is pretty easy to differentiate from other rashes. Two to four days after the other symptoms begin, the rash starts on your hands and face, rather than on your trunk, as most other viral rashes do. It spreads down to the rest of your body and feet over the next few days. Another difference is that your fever usually persists and may get even higher throughout the course of the rash, which lasts for five to six days.

If you think you or your child has measles, call your healthcare provider right away, but don't leave your house unless your practitioner instructs you to. Considering that nine out of 10 unvaccinated people who are exposed to someone with measles get it too, you can end up putting a lot of people at risk.

Your healthcare provider may make special arrangements with you in order to make a diagnosis.

Labs and Tests

Your healthcare provider will look for the very same signs and symptoms you did in your self-check when considering measles, as well as ask about your vaccination and travel history. Even if you've been immunized, it's possible to get measles, though unlikely as two doses of the measles, mumps, and rubella (MMR) vaccine are 94%-97% effective. Suspected cases of measles are required to be reported to local health departments within 24 hours.

To confirm a case of measles, your healthcare provider will likely run some blood tests and take a throat and/or nose swab. These tests detect the virus-specific indirect immunoglobulin M (IgM), an antibody that's usually present about three days after your rash appears. The antibody may not show up before then, will generally peak at day 14, and is usually gone about 30 days after your rash first appears. You may also have a urine sample taken since the measles virus can be present there as well.

Your samples may be sent to your state health department or the Centers for Disease Control and Prevention (CDC) where they may be cultured in order to determine the genotype of the virus. Genotyping can help discover or rule out links between measles cases and outbreaks, as well as distinguish whether you actually contracted the measles virus or you're reacting to a recent measles vaccination.

Measles Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Child

Differential Diagnoses

Your healthcare provider may need to rule out other illnesses before diagnosing you with measles. This is especially true because measles is fairly rare in the United States and most practitioners have never seen anyone with it. That said, measles is fairly easy to diagnose when you know what you're looking for and blood tests can confirm it. Other illnesses your healthcare provider may rule out depend on how long you've been showing symptoms of measles.

Before the Rash Appears

During the few days before the measles rash appears, it may seem like you have a respiratory virus such as the flu, respiratory syncytial virus (RSV), or a rhinovirus, which is typically the virus responsible for the common cold. Two to three days after symptoms begin, the Koplik spots may appear in your mouth. They can be mistaken for Fordyce spots, which are enlarged oil glands.

However, your fever is generally higher with measles than with other viral infections, which is one clue that you don't have a typical viral infection.

Measles can also be mistaken for dengue fever before or after the appearance of the rash, but this can be ruled out with a blood test.

After the Rash Appears

Once the rash has appeared three to five days after your other symptoms, other illnesses that your healthcare provider may want to rule out could include:

  • Other viruses that can cause rashes: These include chickenpox, roseola, rubella, hand-foot-and-mouth disease, and parvovirus, also known as the fifth disease. Usually, healthcare providers can easily rule these other viruses out by how your rash looks, as well as your other symptoms.
  • Scarlet fever and toxic shock syndrome (TSS): These group A Streptococcus infections can cause rashes as well, but scarlet fever can be ruled out by your other symptoms; toxic shock syndrome is usually accompanied by low blood pressure and kidney problems.
  • Reaction to drugs: A rash that's caused by hypersensitivity to a certain drug can look like a measles rash, but your healthcare provider can quickly rule this out if you haven't been recently exposed to any drugs. If there is still a question, it will become obvious once you quit taking the drug because the rash will go away once the drug is out of your system.
  • Meningococcemia: This bacterial infection, which is caused by the same type of bacteria that causes meningitis, may have very similar symptoms to measles, including a rash. A blood test will determine if you have this infection or measles.
  • Rocky Mountain spotted fever: This bacterial disease is spread by ticks and also has similar symptoms to measles, including a rash. It's diagnosed with a blood test or skin biopsy.
  • Infectious mononucleosis: Known to most of us simply as "mono," this viral infection may also present with similar symptoms, including a rash, particularly after you've taken certain antibiotics. A blood test can rule out or confirm mono.

Frequently Asked Questions

  • What illnesses can be mistaken for measles?

    Other illnesses that cause respiratory symptoms and a rash may be mistaken for measles. These could include chickenpox, roseola, rubella, hand-foot-and-mouth disease, fifth disease, scarlet fever, toxic shock syndrome, or an allergic reaction. A healthcare provider can make the diagnosis based on your symptoms, an exam, and a blood test. 

  • What is a titer test for measles?

    Yes. A titer test will show whether or not you have IgG antibodies in your blood, which can mean that you’ve been vaccinated, are immune to measles, or that you were previously infected by the virus and have recovered. Your healthcare provider will take a blood sample to run the test.

  • Should I see a healthcare provider to diagnose measles?

    Yes. Measles is initially diagnosed based on symptoms such as fever, rash, and spots in the mouth. However, it’s possible to mistake these signs for measles instead of other conditions. You should see a healthcare provider to confirm you don't have an illness such as scarlet fever or mononucleosis, which require different treatments. 

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Measles Cases and Outbreaks

  2. Centers for Disease Control and Prevention. Measles (rubeola). Signs and symptoms.

  3. Povey M, Aris E, Cheuvart B, Hall G, Cohet C, Willame C. Effectiveness of "Priorix" against measles and mumps diseases in children born after 2004 in the United Kingdom: A retrospective case-control study using the Clinical Practice Research Datalink GOLD DatabasePediatr Infect Dis J. 2021;40(6):590-596. doi:10.1097/INF.0000000000003111

  4. Centers for Disease Control and Prevention. Measles, Mumps, and Rubella (MMR) Vaccination: What Everyone Should Know

  5. Centers for Disease Control and Prevention. Measles (Rubeola). The Measles Virus Laboratory at CDC

  6. Centers for Disease Control and Prevention. Scarlet Fever: All You Need to Know

  7. Centers for Disease Control and Prevention. Rocky Mountain Spotted Fever (RMSF)

Additional Reading

By Ingrid Koo, PhD
 Ingrid Koo, PhD, is a medical and science writer who specializes in clinical trial reporting