Chapter 7

Diabetes Mellitus

1 Outline the current recommendations for diabetes mellitus screening

Universal screening is not generally recommended. Screening is more accepted, but not universal, in patients who are obese, people older than 45 years of age, people with a family history of diabetes, and members of certain minority groups (black, Hispanic, Pima Indian). Screening in pregnancy is mandatory!

2 Define diabetes

Diabetes is defined when one of the following criteria is met: (1) a glucose level greater than or equal to 126 mg/dL after an overnight (or 8-hour) fast on two separate occasions, (2) a random glucose level greater than 200 mg/dL, or (3) a hemoglobin A1c (Hb A_1c) level of greater than or equal to 6.5% on two separate occasions. If the patient has classic symptoms of diabetes (see question 10), one test is sufficient to make the diagnosis. In an asymptomatic patient, it is best to repeat the test. An oral glucose tolerance test is commonly used in pregnant women; otherwise, it is rarely used because of poor reproducibility and patient compliance. With a glucose tolerance test, diabetes is diagnosed when serum glucose levels in the blood reach or exceed 200 mg/dL within 2 hours of receiving a 75-g oral dose of glucose.

3 What are the classic differences between type 1 and type 2 diabetes?

	TYPE 1 (10% OF CASES)	TYPE 2 (90% OF CASES)
Age at onset	Most commonly < 30 yr	Most commonly > 30 yr
Associated body habitus	Thin	Obese
Development of ketoacidosis	Yes	No
Development of hyperosmolar state	No	Yes
Level of endogenous insulin	Low to none	Normal to high (insulin resistance)
Twin concurrence	<50%	>50%
HLA association	Yes	No
Response to oral hypoglycemics	No	Yes
Antibodies to insulin	Yes (at diagnosis)	No
Risk for diabetic complications	Yes	Yes
Islet-cell pathology	Insulitis (loss of most B cells)	Normal number, but with amyloid deposits

These findings may overlap.

4 What are the goals of treatment in terms of glucose levels?

The goals are to keep postprandial glucose levels less than 180 mg/dL and fasting glucose levels between 70 and 130 mg/dL. Attempts at stricter control may result in hypoglycemia; watch for symptoms of sympathetic nervous system activation and mental status changes.

5 What is a good measure of long-term diabetes control?

A1c measures the “average” control of blood glucose level over the prior 2 to 3 months. The current recommendation is to keep the hemoglobin A_1c level below 7% in most patients. Less stringent A1c goals (e.g., <8%) may be appropriate for patients with a history of severe hypoglycemia, limited life expectancy, advanced microvascular or macrovascular complications, and extensive comorbid conditions.

The Hb A_1c is a good way to catch patients with nocturnal hyperglycemia or less-than-honest patients who falsely record low glucose test readings. A rough rule of thumb is that Hb A1c times 20 equals the average blood glucose level.

6 When a nondiabetic patient presents with hypoglycemia, how can you distinguish between factitious disorder (exogenous insulin) and an insulinoma (endogenous insulin)?

Measure the C-peptide level. C-peptide is produced whenever the body makes insulin, but it is absent in prescription insulin preparations. Therefore C-peptide is high with an insulinoma and low with factitious disorder. This is a classic USMLE question.

7 What should you remember before giving intravenous iodinated contrast material to a patient with diabetes or a patient with renal insufficiency?

Diabetic patients and patients with renal insufficiency are prone to acute renal failure from the intravenously administered iodinated contrast agents used for intravenous pyelography, conventional angiography, and computed tomography (CT). Weigh carefully the risk-benefit ratio of using intravenous contrast agents. If you give contrast, first hydrate the patient well with intravenous fluids to avoid renal shutdown. Acetylcysteine and bicarbonate may decrease the risk of contrast nephropathy in patients at high risk. The concerns about intravenous iodinated contrast do not apply to oral contrast agents (e.g., barium).

8 What is diabetic ketoacidosis (DKA)? How is it treated?

Patients with type 1 diabetes will die without insulin. DKA is a medical emergency that occurs in those patients when their insulin levels become depleted. Clinically, look for Kussmaul breathing (deep, rapid respirations), dehydration, hyperglycemia, acidosis (caused by excessive ketone formation), and increased ketones in the serum (often associated with a fruity odor of the breath) and urine.

Treatment involves intravenous fluids, insulin, and replacement of electrolytes (especially potassium and phosphate). For the USMLE, do not choose to use bicarbonate to correct acidosis. Rather, search for the cause of DKA, which most commonly is noncompliance with insulin therapy. The second most common cause is an infection. The mortality rate of DKA with current treatment efforts is less than 10%.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Vascular Surgery
2. Cholesterol
3. Pulmonology
4. Gastroenterology

Stay updated, free articles. Join our Telegram channel

Join

Full access? Get Clinical Tree