For years, doctors have turned the conventional wisdom about the dangers of high cholesterol on its head when it comes to the many thousands of people on dialysis.
Despite the general acknowledgement that high cholesterol is a risk factor for heart disease and strokes, data have suggested that dialysis patients with high cholesterol have lower death rates than others with supposedly "healthy" blood-lipid levels -- prompting many physicians to refrain from treating dialysis patients with drugs such as statins that can bring cholesterol down.
But a new study of dialysis patients, published last month in the Journal of the American Medical Association, shows that what seemed good about high cholesterol was probably an illusion.
Researchers from the Johns Hopkins Bloomberg School of Public Health found that inflammation and malnutrition -- two serious complications of kidney disease that happen to drive lipid levels down -- were the reasons why the low-cholesterol patients had higher death rates.
"It made low cholesterol seem like it was bad for you," said Dr. Josef Coresh, the study's senior author and a Hopkins professor of epidemiology. "What's actually happening is that the lower cholesterol is a marker for having malnutrition and inflammation."
Settling the issue is not simply a matter of academic interest. Today, about 400,000 Americans are on kidney dialysis, and the number is expected to reach 650,000 by 2010. One in five dialysis patients dies each year, so any treatment that could significantly lower mortality could save thousands of lives each year.
Dialysis is a mechanical method of filtering the blood in patients whose kidneys have shut down, and is often used to keep patients alive until a new kidney is available for transplant. Patients usually require three treatments a week.
It has long been known that kidney disease places people at increased risk for heart attacks and strokes. Logic might dictate that the prospects are worse for patients who also have elevated cholesterol, because the fats have a tendency to collect in the blood vessels and obstruct circulation.
Over the years, however, doctors have shied away from prescribing statins for such patients, in part because of the surprising data showing that dialysis patients with low cholesterol seemed to do worse. The data also fed into a general reluctance to burden sick patients with another medication.
In the latest study, led by Hopkins graduate student Dr. Yongmei Liu, researchers enrolled 823 dialysis patients from 79 clinics in the United States. Besides checking cholesterol, they administered three blood tests to identify which patients showed signs of inflammation and malnutrition. What they found was patients with those complications tended to have low cholesterol and were dying at an abnormally high rate.
"These patients with low cholesterol were having high mortality," said Coresh. "It wasn't because they had low cholesterol, it was because they had something else."
When doctors considered only the dialysis patients who didn't have inflammation and malnutrition, they discovered something else: Lower cholesterol was associated with lower death rates; higher cholesterol with higher death rates.
"What is true is that people who have high cholesterol and who now also have kidney disease have a higher risk of developing heart disease because now they have a combination of factors that's even more deadly," Coresh said.
Dr. Michael Klag, vice dean of the Johns Hopkins School of Medicine and study co-author, said doctors should apply the same standards to treating high cholesterol whether or not the patient has kidney disease or is on dialysis.
"It's very clear that high cholesterol is bad for dialysis patients just as it is for people not on dialysis," said Klag.