Four-Digit Insulin Dosing Code: A simple solution for insulin dosing error

Medication errors continue to be an issue in health care. The Institute of Medicine’s report, To Err is Human: Building a Safer Health System, estimated that medical errors are the eighth leading cause of death in the U.S., with ∼7,000 deaths per year occurring from medication errors (1). Insulin is one of the most frequently cited agents and accounts for 13% of all medication errors (2). Human factors (knowledge or performance deficit, miscalculation or preparation of dosage, transcription errors, fatigue, and computer errors) account for about half (42%) of the medication errors (3). Latin apothecary abbreviations are also prone to misinterpretation. Tenfold insulin overdoses have resulted from the misinterpretation of the abbreviation “U” (for units) as a zero when closely followed by a number of written orders (4). The Institute for Safe Medication Practices recommends spelling out the word “units” for the abbreviation “U.” Similarly, the letter “I ” of IU (international units) may be misinterpreted as the number “1” (5). Recently, I had a case where despite spelling out the word “units,” the patient received 10 times the prescribed dose of insulin because the nurse mistook the letter “U” in the word “Units” for a “0.”

I believe that the following standard code to write insulin orders should be advocated to all health care providers and patients until a computerized physician-order entry system becomes the standard. Using the standard code, insulin dose is prescribed in a code of four numbers, where the first three numbers represent the premeal doses and the last number represents the bedtime dose. A schema is shown in Table 1.

For a patient receiving 10 units NPH insulin at bedtime and 6 units regular insulin before breakfast, 4 units before lunch, and 8 units before dinner, the doses could be simply written as follows. NPH: 0-0-0-10; regular: 6-4-8-0.

Each dose, as shown above, would be separated with a hyphen (-) and not with a slash (/), since a slightly different angle of slash could be mistaken for the number “1.” For patients who are NPO and receiving insulin, the doses could be written in a similar form depending on the frequency of dosing. For example, analog insulin every 4 h may be written as 4-6-5-5-0.

Using this code, no other words or abbreviations that may be mistaken for zero or one (like U or IU) are added after the dose. I find this method to be a simple, safe, and effective communication tool and suggest promoting it as the standard code for insulin dosing to patients and health care professionals around the world.