What’s the difference between Type 1 and Type 2 Diabetes Mellitus?

According to the American Diabetes Association, diabetes mellitus (DM) is a “group of diseases characterized by high blood glucose levels that result from defects in the body’s ability to produce and/or use insulin.” 

Insulin is a hormone that helps the body use glucose for energy.  When we eat food, the body breaks down all of the sugars and starches into glucose, which is the basic fuel for the cells in the body. Insulin takes the sugar from the blood into the cells.

DM is described as Type 1 or Type 2.  In Type 1 DM or juvenile type diabetes (or DM I), the individual is deficient of insulin because the pancreas does not produce. Patients with DM I, or Type 1 DM, take insulin by injection or through a pump that releases the right amount of insulin the patient needs at scheduled times and as needed.

Individuals with Type 2 DM (DM II) have a disorder called insulin resistance.  These patients’ bodies produce insulin but either not in the required amounts, or their cells basically ignore the insulin.  When this happens, the insulin builds up in the blood, which can cause complications.  Patients with Type 2 DM take oral medications to cause the body to release more insulin and also to move the glucose into the cells. Type 2 DM is used as the default type of DM when the clinician does not specify whether the diabetes is Type 1 or Type 2.  Keep in mind that the use of insulin does not determine the type of DM.

The American Diabetes Association has specific criteria for the diagnosis of diabetes.  This diagnosis is made by monitoring the blood sugar level on various types of laboratory tests.  Coders should ensure that their clinicians are aware of the ADA’s guidelines which have been refined over the years.  This is specifically important because some laboratory reports may list different parameters for blood sugar readings which vary from the ADA’s guidelines.

The terminology of insulin-dependent diabetes mellitus (IDDM) and non- insulin-dependent diabetes mellitus (NIDDM) is outdated and was replaced with the terminology above in 2004.  It’s important for coding staff to query the clinician when there are inconsistencies or vague documentation of the condition. It is not unusual for a physician to document DMI on one visit and DMII on another.  In addition, coaching should be employed for those clinicians who still use outdated terms.

From a coding standpoint, DM can be tricky.  The ICD-9-CM guidelines require the coder to select from two basic categories of DM for Type 1 or Type 2:  uncontrolled, which means the patient’s blood glucose is not within normal limits, and not stated as uncontrolled. This last category means the clinician didn’t specify the status of the DM (e.g., didn’t say whether it was controlled or uncontrolled).  This designation is made by means of the fifth digit associated with the diabetes ICD-9-CM code.

In addition, DM can cause complications in the body, which range from acute issues, such as coma or shock, to chronic issues, which include kidney, eye, nerve or circulatory problems.


  • American Diabetes Association (http://www.diabetes.org)
  • Medical Terminology for Health Professions, Ninth Edition by Ehrlich & Schroeder
  • Clinical Pathophysiology Made Ridiculously Simple by Berkowitz
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