What is the difference between 40 IU insulin and 100 IU insulin syringes?
Patient's Query
Doctor, I am really confused about 40 IU insulin and 100 IU insulin. I was recently advised insulin, and when I went to the pharmacy, I saw two types of syringes. In my family, my grandmother once took 100 IU insulin using a 40 IU syringe by mistake.
She developed severe low sugar and had to be admitted to hospital. The doctor later told us that the insulin was correct, but the syringe was wrong. That incident scared me a lot.
Are 40 IU and 100 IU insulins the same or different? Why are there two types? What precautions should we take so that such dangerous mistakes do not happen again?
Doctor Answers
This is a very important and practical question. You are right to be cautious.
40 IU and 100 IU insulin refer to concentration, not strength of the medicine.
- U-40 insulin means 40 units of insulin in 1 ml
- U-100 insulin means 100 units of insulin in 1 ml
So, U-100 insulin is 2.5 times more concentrated than U-40 insulin.
That is why the syringe must always match the insulin concentration.
Why mixing them is dangerous
- If U-100 insulin is drawn into a U-40 syringe, the person receives much more insulin than intended. This can cause severe hypoglycemia, seizures, or even coma.
- If U-40 insulin is drawn into a U-100 syringe, the dose becomes too low, leading to high sugars and poor control.
This is exactly what happened in your grandmother’s case.
Simple way to remember
- U-40 insulin → U-40 syringe only
- U-100 insulin → U-100 syringe only
Never mix and match.
How to identify them
- U-40 insulin usually has a red cap and U-40 marking on the vial
- U-100 insulin usually has an orange cap and U-100 clearly written
- Syringes also have clear markings showing U-40 or U-100
Always read the label before drawing insulin, even if you have been using it for years.
Why two types exist
Historically, U-40 was commonly used in India. Over time, U-100 became the global standard because it allows smaller injection volumes and better accuracy. Today, most modern insulins are U-100.
Key precautions for patients and families
- Never change syringe type without consulting your doctor
- Keep only one type of syringe at home if possible
- Educate elderly family members and caregivers
- If switching from U-40 to U-100 insulin, dose recalculation must be done by a doctor
Insulin itself is safe. Most insulin-related emergencies happen due to dose or syringe mismatch, not because insulin is harmful.
References:
- https://diabetesjournals.org/care/article/27/suppl_1/s106/24690/Insulin-Administration
- https://idf.org/media/uploads/2023/05/attachments-63.pdf
- https://www.mayoclinicproceedings.org/article/S0025-6196(16)30410-4/pdf
- https://www.icmr.gov.in/icmrobject/custom_data/pdf/resource-guidelines/ICMR_Guidelines_for_Management_of_Type_1_Diabetes.pdf
- https://www.icmr.gov.in/icmrobject/custom_data/pdf/resource-guidelines/ICMR_GuidelinesType2diabetes2018_0.pdf
Disclaimer: The information provided in this Q&A is for educational purposes only and should not be considered as medical advice. Always consult with a qualified healthcare professional for personalized medical guidance and treatment recommendations.