MedlinePlus

Health topics, lab test explanations and medical test results

MedlinePlus provides health information from the U.S. National Library of Medicine, including condition and symptom overviews and explanations of tests with matching pages.

Explain lab test

Explain what a MedlinePlus medical test measures, why it may be ordered, how it is done, preparation, risks, and what results mean. Only tests with a matching MedlinePlus Medical Tests page are available.

Your information

Test

Test name on a lab form or report, for example A1C, CBC, or TSH.

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Example results

Hemoglobin A1C (HbA1c) Test

View MedlinePlus test page

Also called

HbA1C
A1C
glycohemoglobin
glycated hemoglobin
glycosylated hemoglobin

What the test measures

A hemoglobin A1C (HbA1C) test is a blood test that shows your average level of blood glucose , also called blood sugar, over the past two to three months. Glucose is a type of sugar in your blood that comes from the foods you eat. Your cells use glucose for energy. A hormone called insulin helps glucose get into your cells. If you have diabetes your body doesn't make enough insulin, or your cells don't use it well. As a result, glucose can't get into your cells, so your blood glucose levels increase. Glucose in your blood sticks to hemoglobin, a protein in your red blood cells. As your blood glucose levels increase, more of your hemoglobin will be coated with glucose. An A1C test measures the percentage of your red blood cells that have glucose-coated hemoglobin. An A1C test can show your average glucose level for the past three months because: • Glucose sticks to hemoglobin for as long as the red blood cells are alive. • Red blood cells live about three months. High A1C levels are a sign of high blood glucose from diabetes. Diabetes can cause serious health problems , including heart disease , kidney disease , and nerve damage . But with treatment and lifestyle changes, you can control your blood glucose levels.

What it is used for

Your blood glucose level changes all the time. If you're checking it at home, you are measuring what your blood glucose level is at that time. An A1C test gives you an average level of your blood glucose level over the past two to three months. An A1C test may be used to screen for or diagnose: • Type 2 diabetes . With type 2 diabetes your blood glucose gets too high because your body doesn't make enough insulin or doesn't use insulin well. The glucose then stays in your blood and not enough goes into your cells. • Prediabetes . Prediabetes means that your blood glucose levels are higher than normal, but not high enough to be diagnosed as diabetes. Lifestyle changes, such as healthy eating and exercise , may help delay or prevent prediabetes from becoming type 2 diabetes. If you have diabetes or prediabetes, an A1C test can help monitor your condition and check how well you've been able to control your blood glucose levels. The A1C test isn't used to diagnose type 1 diabetes but may be used for monitoring your blood glucose levels.

Why you might need it

The Centers for Disease Control (CDC) recommends A1C testing for diabetes and prediabetes if: • You are over age 45. If your results are normal, your provider will tell you how often you should be tested based on your age and risk factors. If your results show you have prediabetes, you will usually need to be tested every 1 to 2 years. Ask your provider how often to get tested and what you can do to reduce your risk of developing diabetes. If your results show you have diabetes, you should get an A1C test at least twice a year to monitor your condition and treatment. • You are under 45 and are more likely to develop diabetes because you: Have prediabetes. Are overweight or have obesity . Have a parent or sibling with type 2 diabetes. Have high blood pressure or high cholesterol levels. Have heart disease or have had a stroke . Are physically active less than 3 times a week. Have had gestational diabetes (diabetes during pregnancy) or given birth to a baby over 9 pounds. Are African American, Hispanic or Latino, American Indian, or an Alaska Native person. Some Pacific Islander and Asian American people also have a higher risk of developing diabetes. Have polycystic ovarian syndrome (PCOS). You may also need an A1C test if you have symptoms of diabetes, such as: • Feeling very thirsty • Urinating (peeing) a lot • Losing weight without trying • Feeling very hungry • Blurred vision • Numb or tingling hands or feet • Fatigue • Dry skin • Sores that heal slowly • Having more infections than usual

What happens during the test

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

How to prepare

Certain medicines such as opioids and some HIV medicines may affect your results, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to. Also, let your health care provider know if you are pregnant, since this may affect your results.

Risks

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What the results mean

A1C results tell you what percentage of your hemoglobin is coated with glucose. The ranges are just a guide to what is normal. What's normal for you depends on your health, age, and other factors. Ask your provider what A1C percentage is healthy for you. To diagnose diabetes or prediabetes, the percentages commonly used are: • Normal: A1C below 5.7% • Prediabetes: A1C between 5.7% and 6.4% • Diabetes: A1C of 6.5% or higher Providers often use more than one test to diagnose diabetes. So, if your test result was higher than normal, you may have another A1C test or a different type of diabetes test , usually either a fasting blood glucose test or an oral glucose tolerance test (OGTT). If your A1C test was done to monitor your diabetes, talk with your provider about what your test results mean. Learn more about laboratory tests, reference ranges, and understanding results .

About the MedlinePlus tool

MedlinePlus provides health-topic overviews and related topics; enter a condition or symptom, and optionally choose a language.

Explain lab test describes what a test measures, why it may be ordered, preparation, risks, and results; enter a test name.

Built from medlineplus.gov. Last checked Sep 29, 2026.

Actions

Explain lab test

1 credit

What you provide

Field	Type	Required	Description
Test`test`	Text	Required	Test name on a lab form or report, for example A1C, CBC, or TSH.Example: A1C

What you get

Field	Type	Description
Risks`risks`	Text	Risks of the test.Example: There is very little risk to having a blood test. You may have slight pain or…
Used for`used_for`	Text	What the test is used for.Example: A complete blood count is often part of a routine checkup . It is also used to…
Page Link`page_link`	Link	MedlinePlus test page.Example: https://medlineplus.gov/lab-tests/hemoglobin-a1c-hba1c-test/
Test Name`test_name`	Text	MedlinePlus name of the test.Example: Hemoglobin A1C (HbA1c) Test
What It Is`what_it_is`	Text	What the test is and measures.
Other Names`other_names`	List	Other names listed on the test page.
What Happens`what_happens`	Text	What happens during the test.Example: A health care professional will take a blood sample from a vein in your arm…
How to Prepare`how_to_prepare`	Text	How to prepare.Example: Certain medicines such as opioids and some HIV medicines may affect your…
What Results Mean`what_results_mean`	Text	Explanation of results.
Why You Might Need It`why_you_might_need_it`	Text	Reasons the test may be ordered.Example: Your health care provider may have ordered a complete blood count as part of…

Example result

For Test: A1C

JSON

{
  "risks": "There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.",
  "used_for": "Your blood glucose level changes all the time. If you're checking it at home, you are measuring what your blood glucose level is at that time. An A1C test gives you an average level of your blood gluc…",
  "page_link": "https://medlineplus.gov/lab-tests/hemoglobin-a1c-hba1c-test/",
  "test_name": "Hemoglobin A1C (HbA1c) Test",
  "what_it_is": "A hemoglobin A1C (HbA1C) test is a blood test that shows your average level of blood glucose , also called blood sugar, over the past two to three months.\nGlucose is a type of sugar in your blood that…",
  "other_names": [
    "HbA1C",
    "A1C",
    "glycohemoglobin"
  ],
  "what_happens": "A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You…",
  "how_to_prepare": "Certain medicines such as opioids and some HIV medicines may affect your results, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to…",
  "what_results_mean": "A1C results tell you what percentage of your hemoglobin is coated with glucose. The ranges are just a guide to what is normal. What's normal for you depends on your health, age, and other factors. Ask…",
  "why_you_might_need_it": "The Centers for Disease Control (CDC) recommends A1C testing for diabetes and prediabetes if:\n• You are over age 45. If your results are normal, your provider will tell you how often you should be tes…"
}

Get health topic

1 credit

Get a MedlinePlus health-topic overview and related topics for a condition or symptom. Encyclopedia sections are included only when a matching article is linked from that topic; unavailable sections are null.

What you provide

Field	Type	Required	Description
Topic`topic`	Text	Required	Condition or symptom to look up, for example shingles or back pain.Example: Shingles
Language`language`	Text	Optional	Language of the overview, for example spanish.Example: Spanish

What you get

Field	Type	Description
Title`title`	Text	MedlinePlus topic title.Example: Shingles
Causes`causes`	Text	Causes from a matching medical encyclopedia article.
Summary`summary`	Text	Plain-text health topic overview.
Symptoms`symptoms`	Text	Symptoms from a matching medical encyclopedia article.
Page Link`page_link`	Text	MedlinePlus health topic page.Example: https://medlineplus.gov/shingles.html
Treatment`treatment`	Text	Treatment from a matching medical encyclopedia article.
Prevention`prevention`	Text	Prevention from a matching medical encyclopedia article.Example: Do not touch the rash and blisters on people with shingles or chickenpox if…
Other Names`other_names`	List	Other names of the health topic.
Related Topics`related_topics`	List	Related MedlinePlus health topics.
Link`related_topics[].link`	Text	Example: https://medlineplus.gov/chickenpox.html
Name`related_topics[].name`	Text	Example: Chickenpox
Exams and Tests`exams_and_tests`	Text	Exams and tests from a matching medical encyclopedia article.Example: Your health care provider can make the diagnosis by looking at your skin and…
When to Contact A Doctor`when_to_contact_a_doctor`	Text	When to contact a medical professional from a matching medical encyclopedia article.Example: Contact your provider if you have symptoms of shingles, particularly if you…

Example result

For Topic: Shingles

JSON

{
  "title": "Shingles",
  "causes": "After you get chickenpox, your body does not get rid of the virus. Instead, the virus remains in the body but is inactive (becomes dormant) in certain nerves in the body. Shingles occur after the viru…",
  "summary": "What is shingles? Shingles (herpes zoster) is an infection that causes a painful rash. It is caused by the varicella-zoster virus (VZV). This is the same virus that causes chickenpox. After you have c…",
  "symptoms": "The first symptom is usually pain, tingling, or burning that occurs on one side of the body. The pain and burning may be severe and are usually present before any rash appears. Red patches on the skin…",
  "page_link": "https://medlineplus.gov/shingles.html",
  "treatment": "Your provider may prescribe a medicine that fights the virus, called an antiviral medicine. This medicine helps reduce pain, prevent complications, and shorten the course of the disease. The medicines…",
  "prevention": "Do not touch the rash and blisters on people with shingles or chickenpox if you have never had chickenpox or the chickenpox vaccine. The shingles vaccine is different than the chickenpox vaccine. Olde…",
  "other_names": [
    "Herpes Zoster",
    "Postherpetic Neuralgia"
  ],
  "related_topics": [
    {
      "link": "https://medlineplus.gov/chickenpox.html",
      "name": "Chickenpox"
    }
  ],
  "exams_and_tests": "Your health care provider can make the diagnosis by looking at your skin and asking about your medical history. Tests are rarely needed, but may include taking a skin sample to see if the skin is infe…",
  "when_to_contact_a_doctor": "Contact your provider if you have symptoms of shingles, particularly if you have a weakened immune system or if your symptoms persist or worsen. Shingles that affects the eye may lead to permanent bli…"
}

For developers

Call it from your code with one request. Change the values in input to run it on new data. To get an API key, open Developers at the bottom of Studio, turn on Developer mode and go to API keys.

cURL

curl 'https://api.fous.com/v1/query' \
  --fail-with-body --silent --show-error --max-time 180 \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H 'Content-Type: application/json' \
  --data-raw '{
  "api": "@medlineplus",
  "visibility": "public",
  "operation": "explain_lab_test",
  "version": 1,
  "input": {
    "test": "A1C"
  },
  "response": {
    "format": "json"
  }
}'

What you can do with it

Research condition causes, symptoms, and treatment options
Find related health topics for a condition
Explain what a lab test measures
Help patients prepare for a medical test
Clarify what test results may mean

Questions about MedlinePlus

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Can I call this MedlinePlus tool as an API?

Yes. Send a POST request to /v1/query with your Fous API key and the inputs, and get JSON back.

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No. You only need a Fous account.

How current is the data?

Fous gets the data from medlineplus.gov when you run it. Some results are reused for up to 24 hours, and results that use your account or key are never reused. It was last verified on Sep 29, 2026.