Case Study: A 57-Year-Old Man With Type 2 Diabetes, Hypertension, and Microalbuminuria
Physical exam reveals a height of 5 feet, 8 inches, weight of 243 lb, blood pressure of 160/100 mmHg, and a regular pulse of 84 beats/min. There is no retinopathy or thyromegaly. There is no clinical evidence of congestive heart failure or peripheral vascular disease.
Laboratory evaluation reveals trace protein on urinalysis, blood urea nitrogen of 14 mg/dl, serum creatinine of 1.2 mg/dl, random serum glucose of 169 mg/dl, normal electrolytes, and normal thyroid-stimulating hormone levels. A 24-h urine collection reveals a urinary albumin excretion rate of 250 mg/day.
Early detection and treatment of albuminuria is essential in diabetes. A normal urinary albumin excretion rate (UAER) ranges from 0 to 30 mg/day. Overt albuminuria or macroalbuminuria is defined as a UAER >300 mg/day. Many studies have shown that a UAER >30 mg/day is abnormal and can be used to predict the development of overt albuminuria or diabetic nephropathy and both microvascular and macrovascular disease. As a result, the term "microalbuminuria" was coined to refer to a UAER of 30299 mg/day.
Many organizations, including the American Diabetes Association, recommend regular screening for microalbuminuria. Type 1 diabetic patients should be screened 5 years after diagnosis of diabetes and after puberty. People with type 2 diabetes should be screened from the time of diagnosis, since many type 2 diabetic patients have had undiagnosed disease for some time. If the initial screening is negative, then annual screenings are indicated.
Traditional urinary dipsticks are insensitive at detecting albuminuria <300 mg/day. Spot urine samples may be assayed for microalbuminuria and creatinine and a ratio >30 µg/mg or mg/g is abnormal. Newer methods, such as Micral-Test II test strips (Boehringer Mannheim, Mannheim, Germany), permit reliable semiquantitative determination of microalbuminuria and can be used in the office for dipstick screening of diabetic patients.
Transient elevations in urinary albumin excretion may be associated with marked hyperglycemia, acute febrile illness, exercise, hypertension, heart failure, and urinary tract infection. If the initial test is elevated, these and other potential causes of renal disease should be considered and ruled out. Because there is also marked day-to-day variability in urinary albumin excretion, a positive test should be confirmed on a subsequent occasion before designating a patient as having persistent microalbuminuria.
Patients identified with persistent microalbuminuria should be aggressively treated both with respect to glycemic and blood pressure control. Patients are considered to be hypertensive if their blood pressure is >140/90 mmHg. The goal for the management of hypertensive diabetic patients is to keep the blood pressure <130/85 mmHg.
The treatment of choice for hypertensive diabetic patients with or without microalbuminuria remains angiotensin-converting enzyme (ACE) inhibitors. Only captopril (Capoten) is approved for the treatment of diabetic nephropathy, but all ACE inhibitors appear to be effective. Fosinopril (Monopril) has a dual route of elimination and therefore may have an advantage over other ACE inhibitors, particularly when used for patients with renal insufficiency or failure.
Once started, renoprotective therapy should be continued indefinitely. ACE inhibitors have been shown to prevent or slow the progression from microalbuminuria to overt nephropathy. Studies have also shown that the renoprotective effects of ACE inhibitors go beyond those expected from blood pressure reduction by itself. Additionally, the renoprotective effects apply to both normotensive and hypertensive patients with microalbuminuria. Therefore, the indication for ACE inhibition can be persistent microalbuminuria, regardless of blood pressure. Discontinuing therapy will result in a recurrence of microalbuminuria.
In addition to aggressively managing blood pressure, attempts need to be made toward lifestyle modifications. These include meticulous control of blood glucose, seeking counseling to stop smoking, maintaining optimal body weight, following an appropriate diet, and exercising regularly.
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Jeffrey A. Luerding, MD, is a family physician in private practice in Kansas City, Mo.
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