Subcutaneous (SC) injections deliver medication into the fatty layer just beneath the skin, also known as the hypodermis. This route is commonly used for self-administration of drugs like insulin, certain hormones, and modern biologic agents because of its relative ease and slow, sustained absorption profile. While errors in technique are certainly possible, most are minor and manageable. This article aims to clarify the specific ways an SC injection can go wrong and explain how to ensure the medication is delivered correctly.
Identifying Common Errors in Technique
A fundamental mistake involves inserting the needle at an incorrect angle, which dictates the depth of penetration. The goal is to deposit the drug into the fatty layer, avoiding both the shallow skin (intradermal) and the deeper muscle (intramuscular or IM). For individuals with a standard amount of subcutaneous fat, a 90-degree angle is generally appropriate, especially when using shorter needles common with modern pen devices.
A shallower 45-degree angle is recommended for thinner individuals or children to ensure the needle does not reach the muscle tissue. Injecting into the muscle results in faster drug absorption, which can drastically alter the intended effect of a medication like insulin, potentially leading to unpredictable blood sugar fluctuations. Conversely, injecting too shallowly into the skin can cause a small, painful bubble or blister.
Errors also frequently occur with skin preparation and handling during the injection process. Many devices and techniques require pinching a fold of skin to elevate the fat layer and separate it from the muscle. Improper pinching—either too loosely or releasing the pinch too early—can compromise the intended depth of the injection.
The speed at which the medication is pushed into the tissue can also cause discomfort or leakage. Injecting the fluid too quickly can create pressure in the small subcutaneous space, leading to pain and potentially causing the medication to seep back out of the needle path when the syringe is removed. After injection, the needle should be held in place for a few seconds, typically a count of five to ten, before withdrawal to allow the liquid to disperse into the fatty tissue.
Site Selection and Rotation Mistakes
Improper placement of the injection is a frequent error that can lead to long-term tissue changes. Approved areas for SC injections include the abdomen, the outer thighs, and the back of the upper arms, as these sites typically have sufficient fatty tissue. Injecting too close to joints, bones, or major nerves can cause severe pain or injury.
A common and significant mistake is repeatedly injecting into the exact same small area, which can damage the local tissue. The practice of site rotation requires moving the injection location for every dose, maintaining at least a centimeter of distance from the previous puncture site. Ignoring this rotation principle causes localized trauma and can lead to the formation of abnormal tissue structures over time.
Another selection error involves injecting into compromised skin tissue. Areas with existing bruises, moles, scars, or signs of infection should be strictly avoided. Injecting into unhealthy or damaged tissue can interfere with the medication’s absorption and increase the risk of introducing bacteria into the site. The abdomen is often a preferred site, but injections must be kept away from the belly button area.
Consequences of Injection Errors
When medication is inadvertently delivered into the muscle instead of the fat layer, the most significant outcome is altered drug absorption. Muscle tissue is more vascularized, meaning it has a richer blood supply than subcutaneous fat, leading to a much faster rate of absorption. For medications designed for slow release, like certain types of insulin, this can cause a rapid, unexpected spike in the drug’s effect, risking hypoglycemia or other adverse effects.
Repeatedly injecting into the same spot can result in lipodystrophy, a physical change in the fat tissue. This can manifest as lipohypertrophy, which are firm, raised lumps or scarring, or the less common lipoatrophy, which is a localized indentation where the fat tissue has wasted away. Injecting into these scarred or lumpy areas leads to highly erratic and unpredictable drug absorption, making consistent dosing and therapeutic control difficult.
Immediate, non-serious consequences are also common, often resulting from mechanical errors. Pain, minor bruising, and a small amount of bleeding are frequent occurrences, often caused by nicking a small blood vessel or injecting too quickly. While minor, these consequences can cause anxiety and should prompt a review of the injection technique.
A more concerning outcome is the risk of infection, typically resulting from poor hygiene practices. Reusing needles, failing to clean the injection site, or touching the sterilized area before injection can introduce bacteria. Signs of infection include persistent redness, swelling, warmth, and increased pain at the site, which may require medical attention.
Troubleshooting and Ensuring Correct Delivery
Before every injection, a quick pre-injection check minimizes the chance of error and contamination. This involves inspecting the medication for clarity or proper consistency and ensuring the injection device is functioning correctly. The chosen injection site must be cleaned with an alcohol swab and allowed to dry completely before needle insertion to prevent the sting of the alcohol and reduce the risk of infection.
If a small amount of blood or medication leaks out after the needle is removed, it is usually not a cause for concern and does not mean the entire dose was lost. Gentle pressure applied to the site with a cotton ball or gauze for a few seconds can help seal the puncture and prevent further leakage. Counting slowly to ten before withdrawing the needle ensures the medication has had time to disperse completely into the fatty tissue.
Individuals should seek professional medical advice if they experience signs of infection, such as fever or persistent discharge from the site. Persistent, hard lumps that do not resolve, or unexplained changes in medication effectiveness, such as erratic blood sugar readings, also warrant a consultation. Consistent training refreshers with a healthcare professional are important to maintain proper technique.