NPH insulin is a common type of insulin used to manage blood sugar levels in individuals with diabetes. Many people wonder if it is supposed to be cloudy. This article explains why NPH insulin has its characteristic appearance, how to prepare it, what problematic changes to look for, and essential storage guidelines.
Understanding NPH Insulin’s Appearance
NPH insulin, also known as isophane insulin, is deliberately designed to have a cloudy or milky appearance. This distinctive look results from the addition of protamine and zinc to the insulin. These substances bind with the insulin, forming a suspension of tiny crystals that slow down its absorption into the bloodstream, providing a longer-lasting effect. The term “NPH” stands for Neutral Protamine Hagedorn, referencing its neutral pH, added protamine, and developer Hans Christian Hagedorn.
The normal appearance of NPH insulin is uniformly cloudy or milky, resembling skim milk. After sitting for a while, the solid particles may settle at the bottom, leaving a clearer liquid on top. This separation is expected and does not indicate a problem, as long as the particles can be easily resuspended.
Proper Preparation Before Injection
Given its suspended nature, proper mixing of NPH insulin is essential to ensure a consistent and accurate dose. Before each injection, the vial or pen containing NPH insulin should be gently mixed. This involves rolling the vial or pen between the palms of your hands at least ten times, followed by inverting it end-over-end ten times. This gentle action helps to uniformly redistribute the insulin particles throughout the liquid.
It is important to avoid vigorously shaking NPH insulin. Shaking can create air bubbles, which can make it difficult to draw an accurate dose and may potentially alter the insulin’s effectiveness. After proper mixing, the insulin should appear uniformly cloudy or milky with no clear layers or visible particles stuck to the sides or bottom.
Identifying Problematic Changes
While a cloudy or milky appearance is normal for NPH insulin, certain changes indicate that the insulin may be compromised and should not be used. Inspecting the insulin before each use is an important safety measure. For instance, if you observe clumps, crystals, or a frosted appearance on the inside of the vial or pen, the insulin should be discarded. These visual cues suggest the insulin has lost its stability.
If NPH insulin becomes clear or changes color, it is no longer safe to use. These alterations can signify a loss of potency or contamination, meaning the insulin may not effectively control blood sugar levels. In such cases, the insulin should be discarded and replaced with a new supply.
Storage Guidelines
Proper storage is important for maintaining the stability and effectiveness of NPH insulin. Unopened vials or pens of NPH insulin should be stored in a refrigerator, typically between 36°F and 46°F (2°C and 8°C), until their expiration date. Freezing insulin can damage it and render it ineffective, so it should never be frozen.
Once opened or in use, NPH insulin can be stored at room temperature (59°F to 86°F / 15°C to 30°C) for up to 28 days. However, specific brands may have slightly different recommendations, so checking the product insert is advisable. Protecting insulin from direct heat, light, and extreme temperatures is important, as improper storage can lead to a loss of potency and can alter its appearance.