Insulin
Insulin is the hormone that moves sugar from your blood into your cells. This test shows how much is in your blood, usually after fasting.
AI-verified against cited sources. Awaiting expert reviewAlso called IRI, INSLOINC 20448-7
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What it is
Insulin is made by your pancreas. After you eat, your blood glucose rises, and the pancreas releases insulin so your cells can take up the sugar for energy. A blood insulin test measures how much insulin is in your blood at the time of the draw. It is usually done after fasting, together with a glucose test, so the two numbers can be read side by side.
Why it matters
Insulin and glucose normally rise and fall together, so the pair tells a clinician more than either alone. When cells respond poorly to insulin (insulin resistance), the pancreas can make extra to keep glucose in range, so insulin may be high while glucose still looks usual. When the pancreas makes too little insulin, glucose runs high. When glucose is low, an insulin level helps show whether too much insulin is the cause. Insulin is not used on its own to diagnose diabetes or prediabetes, which rely on glucose and A1c.
If it’s low
Insulin and glucose normally rise and fall together, so low insulin with low or normal glucose is expected, especially after a long fast. If insulin is low while glucose is high, the pancreas may not be making enough insulin, which can happen in type 1 diabetes and in pancreatitis. Your clinician will read the two numbers together.
Common causes
- A long fast, which normally lowers insulin
- Type 1 diabetes
- Pancreatitis or other damage to the pancreas
What can help
- Ask your clinician how your glucose and A1c fit with this result
- Ask whether other tests, such as C-peptide, would show how much insulin your body makes
If it’s high
A high insulin level on its own doesn't say much, because insulin rises with glucose. If insulin is high while glucose is normal or only a little high, the body may be making extra insulin because cells aren't responding to it well (insulin resistance). If insulin is high or normal while glucose is low, too much insulin may be behind the low glucose, and clinicians may order other tests such as C-peptide or proinsulin.
Common causes
- A sample that wasn't fasting, since eating raises insulin
- Insulin resistance, which is more common with prediabetes, type 2 diabetes and polycystic ovary syndrome (PCOS)
- Hormone conditions such as Cushing's syndrome
- Insulin medicine that you inject, which some tests can detect
- Rarely, an insulin-making tumor of the pancreas (insulinoma)
What can help
- Ask your clinician whether a repeat fasting test, with glucose measured at the same time, would help
- Regular physical activity, a balanced eating pattern and a healthy weight are the main lifestyle levers clinicians discuss for insulin resistance
- Ask whether your glucose, A1c and lipid results should be reviewed together with this one
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 2.6–24.9 µIU/mL. Source: Labcorp, ARUP Laboratories, MedlinePlus, National Library of Medicine, Diabetes Care, CDC National Center for Health Statistics.
- Adults (this one applies)2.6–24.9 µIU/mL
Sources: Labcorp, ARUP Laboratories, MedlinePlus, National Library of Medicine, Diabetes Care, CDC National Center for Health Statistics
See Insulin by age and sex, with the U.S. survey numbers where they exist.
If this applies to you
Insulin means a little more for some people. Open the one that fits you.
Tracking for long-term health
An ADA workgroup reported in 2010 that commercial insulin tests give a range of values for the same sample, so fasting insulin results from different labs are not directly comparable. A 2023 international guideline on PCOS (also called PMOS) says insulin tests in clinical use are of limited value and not recommended in routine PCOS care.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Insulin by age and sex: every percentile as a table, with a download.
What can affect your result
- Fasting: eating raises insulin, so the sample should be fasting (usually 8 to 12 hours)
- Your glucose level at the time of the draw
- Biotin supplements, which can interfere with some tests
- Insulin antibodies and insulin medicines you inject
- Which assay the lab uses: assays aren't standardized, so ranges differ between labs
- High-dose biotin (vitamin B7) can interfere with some insulin immunoassays. Labcorp asks you to stop biotin at least 72 hours before the draw, and MedlinePlus says at least a day. Check with your clinician before stopping any supplement.
- Insulin antibodies and monoclonal mouse antibodies in the blood can distort results (Labcorp).
- Injected insulin medicines are measured differently by different tests. Labcorp's assay reads under 1% of aspart, glargine and lispro, while ARUP's reads them almost fully.
- Not fasting: a recent meal raises insulin, so a non-fasting result cannot be compared with a fasting range.
- Serum should be separated and kept cool. Labcorp lists stability of 1 day at room temperature and 14 days refrigerated or frozen.
Morning, after an 8 to 12 hour fast. Reflects the moment of the draw. It rises and falls with glucose within hours of eating.
When to talk to a clinician
Symptoms of low blood sugar, such as sweating, shakiness, a racing or irregular heartbeat, confusion, dizziness, headache or hunger, are worth a call to your clinician. Fainting or seizures need emergency care, so call 911 or your local emergency number. An insulin result is usually read with a glucose result, so ask your clinician how the two fit together.
Questions you could ask
- Which range is my lab comparing this with, and should I use the same lab next time?
- Was this a fasting sample, and should we repeat it with a glucose test at the same time?
- How do my insulin, glucose and A1c look together?
- Could any supplement or medicine I take affect this result?
- How do my glucose and A1c fit with this insulin level?
- Do I need other tests to understand how much insulin my body makes?
Questions people ask
What is a normal fasting insulin level?
Labcorp's reference interval is 2.6 to 24.9 µIU/mL, and ARUP's is 3 to 25 µIU/mL. Other labs print different ranges because insulin tests aren't standardized, so use the range on your own report. A single number also depends on your glucose at the time, so it is usually read together with glucose.
Are µIU/mL and mIU/L the same? How do I convert to pmol/L?
Yes, 1 µIU/mL equals 1 mIU/L. To get pmol/L, multiply by 6.0 (the factor used by the US NHANES survey and by ARUP), so 10 µIU/mL is about 60 pmol/L. Some labs use a slightly different factor, so converted numbers can differ a little.
Do I need to fast, and what about biotin?
Yes, usually for 8 to 12 hours, because eating raises insulin. Biotin (vitamin B7) supplements can interfere with some insulin tests, and Labcorp asks you to stop biotin at least 72 hours before the draw. Check with your clinician before changing any supplement.
Can this test diagnose insulin resistance or diabetes?
No. Prediabetes and diabetes are diagnosed with glucose and A1c, not insulin. Some clinicians use insulin together with glucose to estimate insulin resistance, but the tests aren't standardized and there is no single cutoff that works for every lab.
Does injected insulin show up on this test?
It can, depending on the test and the type of insulin medicine. Labcorp's assay reads under 1% of aspart, glargine and lispro, while ARUP's reads them almost fully. If you take insulin, tell your clinician, because the result may not reflect what your own pancreas makes.
Show the science and sources
Units
- 1 µIU/mL = 1 µIU/mL
- 1 µIU/mL = 1 mIU/L
- 1 µIU/mL = 6 pmol/L
Open the Insulin unit converter
Is a change real?
Insulin naturally varies about 25.3% from test to test in the same healthy person. Between two results from the same lab, a rise of 101% or more, or a fall of 50% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Biological variation of serum insulin: updated estimates from the European Biological Variation Study (EuBIVAS) and meta-analysis (Carobene A et al.).
For clinicians and researchers
Serum or plasma insulin is measured by immunoassay. Labcorp uses an electrochemiluminescence immunoassay on Roche cobas systems, and NHANES 2017-2018 used a two-site immunoenzymometric assay on the Tosoh AIA. Commercial assays use different antibodies and calibrators and can give a range of values for the same sample. For this reason a 2010 workgroup recommended standardization against an isotope-dilution mass spectrometry reference procedure and reporting in SI units (pmol/L), and it used a monomeric insulin mass of 5,808 Da to assign molar values (Staten 2010). Units: 1 µIU/mL equals 1 mIU/L. NHANES and ARUP convert to pmol/L at 6.0 per µIU/mL; other conversion factors appear in the literature, so converted values from different sources may not match exactly. Labcorp's assay shows under 1% cross-reactivity with aspart, glargine and lispro, while ARUP's fasting insulin assay reacts nearly equimolarly with those three analogs (about 50% with detemir, under 3% with glulisine). Insulin antibodies and monoclonal mouse antibodies can interfere, as can biotin. ADA diagnostic criteria use glucose and A1C, not insulin. Fasting insulin is paired with fasting glucose to derive indices such as HOMA-IR. Because assays are not standardized, a threshold from one assay does not transfer cleanly to another. In suspected excess insulin with low glucose, clinicians pair insulin with glucose, C-peptide and proinsulin (MedlinePlus).
LOINC 20448-7 (primary), 27873-9, 30363-6, 14796-7, 59179-2, 3695-4. Specimen: serum-or-plasma.
Sources
- Insulin (test 004333), Labcorp
- Insulin in Blood, MedlinePlus, National Library of Medicine
- Insulin assay standardization: leading to measures of insulin sensitivity and secretion for practical clinical care, Diabetes Care (2010)
- NHANES 2017-2018 Insulin (INS_J) data documentation, CDC National Center for Health Statistics (2020)
- Insulin, Fasting (test 0070063), ARUP Laboratories
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.