Insulin is a hormone that helps regulate blood sugar levels. For people with diabetes who require insulin therapy, knowing how much insulin to take is an important part of managing their condition. But with different types of insulin and various delivery methods, it can be confusing to understand insulin dosing. Specifically, when it comes to dosing insulin, one common question is: how many mL is 1 unit of insulin?
What is Insulin?
Insulin is a hormone made by the pancreas that allows cells throughout the body to absorb and use glucose from the bloodstream. After eating, blood glucose levels rise as food is digested and glucose enters the blood. In response, the pancreas releases insulin into the bloodstream. Insulin acts as a “key” that unlocks body cells and allows glucose to enter and be used for energy production. Without insulin, cells cannot absorb glucose properly and blood sugar levels can become dangerously high.
People with diabetes don’t produce enough insulin or are insensitive to its effects. As a result, they need to take additional insulin to control their blood sugar. This is done through insulin therapy, which involves injecting or infusing insulin. There are a few different types of insulin used for diabetes treatment:
- Rapid-acting insulin – Starts working within 15 minutes, peaks in 1 hour, lasts 2 to 4 hours
- Short-acting insulin – Starts working in 30 minutes, peaks in 2 to 3 hours, lasts 3 to 6 hours
- Intermediate-acting insulin – Starts working in 1 to 3 hours, peaks in 4 to 12 hours, lasts 12 to 18 hours
- Long-acting insulin – Starts working in 3 to 4 hours, has no peak, lasts 20 to 24 hours
These insulins differ in how quickly they start working, when they peak, and how long they last. This allows various options for matching insulin action with meals and blood sugar needs throughout the day and night.
Insulin Administration
There are several ways that insulin can be administered:
- Syringes – Insulin syringes allow patients to draw up and inject a precise insulin dose.
- Insulin pens – Pens contain cartridges of insulin with dial or push-button mechanisms for selecting and injecting a dose.
- Insulin pumps – Pumps are programmed to continuously deliver small doses of rapid-acting insulin throughout the day and night. Patients can also deliver a bolus dose at meals or to correct high blood sugar.
- Jet injectors – These devices use high pressure to propel a fine spray of insulin through the skin.
- Inhaled insulin – Rapid-acting insulin that is inhaled as a powder or aerosol for absorption through the lungs.
No matter the delivery method, insulin dosing is prescribed and adjusted in insulin units. Understanding how many mL are in each insulin unit is necessary for drawing up the proper dose.
What is an Insulin Unit?
An insulin unit (U) is a standardized measure for dosing insulin. It provides a way to quantify insulin strength in a consistent manner across different insulin types, concentrations, and devices.
One insulin unit is defined as:
- 1 unit of insulin glargine (Lantus)
- 1 unit of insulin detemir (Levemir)
Most other insulin concentrations are referenced to these long-acting insulins. Shorter-acting insulins like lispro (Humalog) and aspart (Novolog) are also engineered to have a potency equivalent to 1 unit of the long-acting insulins.
Insulin Concentrations
While 1 unit of insulin has a standardized definition, the actual concentration of insulin can vary between products. Insulin concentrations are expressed as:
- U-100 – 100 units of insulin per mL
- U-200 – 200 units of insulin per mL
- U-300 – 300 units of insulin per mL
- U-500 – 500 units of insulin per mL
U-100 insulin is by far the most common. However, some insulin products come in more concentrated forms like U-200, U-300, and U-500.
The concentration affects how much volume contains 1 insulin unit:
- U-100 insulin – 1 unit per 1 mL
- U-200 insulin – 1 unit per 0.5 mL
- U-300 insulin – 1 unit per 0.33 mL
- U-500 insulin – 1 unit per 0.2 mL
So when dosing insulin, it’s important to know the concentration so you draw up the right amount of liquid for the prescribed units.
How Many mL are in 1 Insulin Unit?
Based on standard U-100 insulin concentrations, 1 insulin unit equals:
- 1 unit = 1 mL
So for common U-100 insulins like Humalog, Novolog, Lantus, and Levemir:
- 1 unit of insulin = 1 mL of insulin
However, for more concentrated insulins, 1 unit would be a smaller volume:
- U-200 insulin – 1 unit = 0.5 mL
- U-300 insulin – 1 unit = 0.33 mL
- U-500 insulin – 1 unit = 0.2 mL
The concentration is always listed clearly on insulin packaging and prescripions to avoid confusion. But most people use U-100 insulin. So for simplicity:
- 1 insulin unit = 1 mL of U-100 insulin
Insulin Syringe Markings
Insulin syringes are specifically designed for measuring insulin doses in units. The barrel of the syringe will be marked with insulin unit demarcations.
Common insulin syringe sizes include:
- 1 mL syringes marked per 1 unit
- 0.5 mL syringes marked per 0.5 units
- 0.3 mL syringes marked per 0.5 units
So a 1 mL (100 unit) syringe will have markings from 1 unit all the way up to 100 units. The 1 mL volume encompasses the entire 100 units. For U-100 insulin, the 1 mL syringe scale matches up perfectly with the dose units.
With the 0.5 mL and 0.3 mL syringes, the volumes correlate to 50 units and 30 units respectively. But the unit scale remains standardized. So for 1 unit doses, only a small portion of the syringe barrel is used.
The insulin syringe demarcations allow you to accurately measure and draw up the insulin dose based on the prescribed units, taking the guesswork and math out of figuring mLs.
How to Measure Insulin Doses
Here is a step-by-step guide for measuring insulin doses:
- Check the insulin concentration – Make sure you know whether it is U-100, U-200, U-300, or U-500. This determines the mL per unit.
- Select the appropriate syringe size – Choose a syringe where the unit demarcations match the total dose that needs to be drawn up. Using a 1 mL syringe is most straightforward for U-100 insulin.
- Draw air into the syringe – Pull the plunger back to the number of units you need to draw up. This equates to the same number of mL.
- Inject air into insulin vial – Inject the air from the syringe into the vial to equalize pressure for withdrawing the insulin.
- Invert vial and withdraw insulin dose – Turn the vial upside down and slowly pull back on the plunger until the top edge lines up with your prescribed dose in units.
- Tap out air bubbles – Gently tap the syringe to make any air bubbles rise to the top, then push them out by moving the plunger upward.
- Inject dose – Clean injection site with alcohol, pinch up skin, insert needle into fatty tissue at 90 degree angle, and inject insulin by pushing in the plunger.
- Dispose syringe safely – Do not recap needle. Place used syringe in a puncture-proof disposal container.
Always follow your doctor’s instructions for selecting syringe type, drawing up, and injecting your prescribed insulin dose. With some practice, measuring in units will become second nature.
Frequently Asked Questions
Does the type of insulin change how many mL are in 1 unit?
No, 1 unit of insulin is defined as 1 unit of the long-acting insulins Lantus or Levemir, regardless of insulin type. So 1 unit = 1 mL for all U-100 insulins.
How do I switch between U-100 and more concentrated insulins?
Use extra caution when transitioning between U-100 and more concentrated insulins like U-200 or U-500. The volume that makes up 1 unit differs. Follow your doctor’s specific dosing instructions closely.
Should I use an insulin pen or syringe?
Insulin pens or syringes both allow accurate dosing in insulin units. Pens are more convenient but syringes give more flexibility with dose volumes. Check with your doctor about which method is preferred for your insulin regimen.
What if I don’t have an insulin syringe?
You should always use an insulin syringe designed specifically for measuring doses in units. However, in an emergency, 1 unit of U-100 insulin would approximately equal 0.01 mL on other syringe types.
How do I know if my insulin is U-100 or another concentration?
The concentration should always be printed clearly on your insulin vial or box. If ever unsure, do not guess – contact your pharmacist or doctor to verify the units per mL.
The Takeaway
Understanding insulin concentrations and dosing in units rather than volume can be confusing at first. But with U-100 insulin, the most common concentration, 1 insulin unit equals 1 mL. Insulin syringes simplify the process by allowing patients to directly draw up and measure prescribed doses in units. Always be sure to check the insulin concentration and use the syringe sized for your dose. With practice, you will become proficient at measuring insulin doses accurately and confidently.
