It's widely known that diseases such as high blood pressure (hypertension) and diabetes I can go undetected for quite some time. But few patients—and a relatively small percentage of doctors—realize that chronic kidney disease (CKD) is equally threatening and often remains hidden.
Danger: CKD—and subsequent kidney damage—can be markedly slowed with medications and also by controlling the underlying causes. Yet many primary care physicians don't fully understand how to diagnose this condition or how to assess the main risk factors.
Result: Many of the estimated 20 million Americans with CKD aren't diagnosed as early as they could be. By the time symptoms appear, the kidneys could have lost more than 75% of their normal function. At that point, the damage may be so extensive that patients will eventually require dialysis or a kidney transplant—or they die waiting.
Simple blood and urine tests can detect most cases of early CKD. Patients who are diagnosed and referred to a nephrologist (kidney specialist) early are often able to delay dialysis or transplant, or even avoid them altogether.
WHAT'S GETTING MISSED?
One of the main functions of the kidneys is to eliminate wastes, such as urea, from the body. In CKD, damage to the filtering units (nephrons) in the kidneys is typically caused by hypertension or diabetes, usually over a period of decades. About 45% of CKD cases are caused by diabetes, while 27% are caused by hypertension. Because CKD causes no symptoms, laboratory tests are the only way to detect it early.
That's why patients with hypertension, diabetes or other risk factors for CKD should have tests for kidney function during annual exams. But even that might not be enough. A new study reports that many doctors miss the signs of early CKD even when those signs should be apparent to them.
The study: Researchers at Johns Hopkins University School of Medicine asked 304 randomly selected US doctors, including kidney specialists, internists and family physicians, to evaluate the medical files of a fictitious patient.
The doctors also were given the raw data needed to calculate the glomerular filtration rate, afi important measure of kidney function. They were asked to calculate this number themselves using accepted equations.
Result: Of the kidney specialists surveyed, 97% accurately diagnosed CKD, and 99% of those said they would have recommended that a primary care physician refer the patient to a kidney specialist. Among the internists, only 78% made the proper diagnosis of CKD, and 8\o/o of those recommended a referral to a kidney specialist. Even worse, only 59% of the family physicians made an accurate diagnosis of CKD, and only 76% of those recommended a specialist referral.
The implications of this study are troublesome. Delays in diagnosing CKD greatly increase the risk for complications, including heart disease.
New finding: CKD promotes atherosclerosis and is an independent risk factor (like smoking, diabetes or hypertension) for cardiovascular disease.
Blood and/or urine tests, when interpreted properly, can easily detect early CKD, but doctors don't order these tests as often as they should. Patients who have been diagnosed with diabetes or hypertension should insist on getting tested for CKD. This is particularly important for African-Americans. They are six times more likely than Caucasians to develop hypertension-related kidney failure. People age 60 or older—even if they don't have diabetes or hypertension—also may want to be tested, because they are at higher risk for CKD. The testing can be done by a primary care physician. Main tests…
- Serurn creatinine. CKD curbs the ability of the kidneys to remove wastes from the body. One such waste is creatinine (a substance derived from protein metabolized in muscle). Elevated levels in the blood indicate kidney disease.
Trap: Creatinine alone is not a good marker of kidney function. An older adult, or someone with a small frame, could have a normal level of creatinine and still have CKD. An additional step (below) is needed for accurate results.
- Modification of Diet in Renal Disease equation. Many physicians aren't aware of this equation. It's considered the gold standard for calculating glomerular filtration rate, the best measure of kidney function. The equation, which is available to physicians on the National Kidney Foundation Website (www.kidney.org), takes into account the creatinine level as well as the patient's age, gender, race and other factors.
- Albumin. This is a protein that's often present in the urine of patients with CKD. It's detected by dipping a test strip in a urine sample. The presence of albumin usually indicates kidney damage caused by diabetes. This test is mainly recommended for patients with diabetes or other risk factors for CKD.
- Cystatin C. This is a relatively new test—and might be more accurate than creatinine for diagnosing CKD. Cystatin C is a protein that's normally filtered out of the blood by the kidneys. Elevated levels indicate that the kidneys aren't working at optimal levels.
Apart from a transplant operation, there isn't a cure for CKD. The most important strategy is to control (or prevent) hypertension and diabetes through medication and lifestyle changes, such as following a low-fat, low-salt diet. These conditions can double or triple the risk of CKD—and accelerate the damage in patients who already have it.
Because many patients with CKD also have hypertension, doctors often prescribe blood pressure medication. Lowering blood pressure to below 120/80 mmHg can significantly slow the progression of CKD. These drugs also are helpful for patients with CKD caused by diabetes.
Important: Studies have shown that using an angiotensin converting enzyme (ACE) inhibitor, such as captopril (Capoten) or ramipril (Altace), or angiotensin II receptor blocker, such as irbesartan (Avapro) or candesartan (Atacand), can slow the progression of CKD byas much as 30%. These drugs are effective even in CKD patients who don't have hypertension or diabetes.