Insulin therapy has multiple forms and applications in type 2 diabetes (Table 1). Some of these indications are temporary, such as during an acute illness, in pregnancy, and when those taking metformin are at risk for renal insufficiency or other factors predisposing to lactic acidosis. Insulin is also indicated as initial therapy when individuals present with severe hyperglycemia (fasting glucose over 300 mg/dl or random glucose values over 400 mg/dl) with significant symptoms such as severe polyuria, severe fatigue, and weight loss.
Obviously, insulin is often initiated as permanent therapy after a period of oral agent therapy when the insulin secretory defect has progressed to the point where insulin secretagogues are no longer able to supply adequate insulin to prevent severe hyperglycemia, even in the presence of complementary insulin sensitizers. At other times, insulin may be required earlier than normally expected because of intolerance or contraindications to one or more oral agents. For example, both metformin and thiazolidinediones are contraindicated in congestive heart failure, and insulin will be needed as soon as secretagogues alone fail to control glucose.
We have become increasingly aware of a diagnostic dilemma relevant to
Table 1 Indications for Insulin in Type 2 Diabetes Temporary insulin therapy
At initial diagnosis if the patient has symptomatic severe hyperglycemia Pregnancy
Acute intercurrent illness with glucose decompensation
During steroid therapy
End-stage renal disease
During acute Ml or CVA When metformin is discontinued due to increased risk of lactic acidosis Fear of renal insufficiency due to intravenous dyes Hypoperfusion states such as sepsis or hypotension During parenteral or enteral alimentation Ketosis or hyperosmolar state
In CHF when metformin and thiazolidinediones are contraindicated and other agents fail to control glucose When it is determined that patient may actually have latent autoimmune diabetes in adults (LADA) rather than type 2 diabetes When oral combination therapy is not tolerated or fails to maintain HbAlc under 7.0%
the differential diagnosis of the type of diabetes in adults. As opposed to the clinical presentation of type 1 diabetes in youth, adults may experience a more insidious onset and may respond to oral agents initially (8). This diagnosis is sometimes referred to as latent autoimmune diabetes of adults (LADA). This differentiation is generally made on clinical grounds. The diagnosis of type 1 diabetes should be considered when individuals have no family history of type 2 diabetes, are thin, and have an atypical treatment course. For example, if glucose levels are highly labile on oral agents or if there is failure of an oral therapy within a year, the diagnosis should be reconsidered.
There is no simple standardized laboratory method of differentiating these two main forms of diabetes. There is no standard for use of individual c-peptide levels in this setting, and stimulated c-peptide has been used only as a research test. The presence of anti-GAD (glutamic acid decarboxylase) antibodies or islet cell antibodies can be helpful, but the reliability of either test individually is only about 75% and it is not certain that commercial antibody tests are equivalent to those used in research.
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