Keeping the Filters Working

The victims of kidney disease who make headlines are those whose kidney breakdown is so bad that they need the most dramatic and resourceful treatment--the use of an artificial kidney, or, most daring of all, a kidney transplant. But in all the world probably no more than 300 renal-disease patients have had transplants. In the entire U.S., patients being kept alive with an artificial kidney number hardly more than 50.

But in their less spectacular form, kidney diseases are among the most common causes of illness and death. Most patients recover, but each year in the U.S. 45,000 die of insufficient kidney function. Dr. E. Hugh Luckey, physician-in-chief at the New York Hospital-Cornell Medical Center, cited this somber statistic as introduction to a pair of hour-long seminars on renal diseases broadcast by New York's educational WNYC-TV Channel 31. Sponsored by the New York Academy of Medicine, the programs gave general practitioners and internists the latest word on diagnosis and treatment--much of it new knowledge gained since most of them got out of medical school.

Micrometer Precision. About as big as its owner's fist, the human kidney is a biochemical filter with incredibly delicate powers of discrimination. It is also a prodigious worker (see diagram, left). All the water that anyone consumes in food or drink must go into the blood and be extracted by the kidneys before it can be voided as urine--contrary to the beer drinker's cliche "It goes right through you." Kidneys also work fast: the malodorous sulphur compound in asparagus is extracted and begins to be excreted in a couple of hours.

Each kidney contains a million filtration units called nephrons. Each nephron is made up of a tuft of microscopic blood vessels, called a glomerulus, and each of these has a minute tubule at tached (see diagram, right). When blood flows into the glomeruli and around the tubules, one-fifth of its water content is led aside for finer filtration. One hundredth part of this is extracted and passes eventually to the bladder.

The nephrons' job is to let only water and waste chemicals get through; they must hold all red cells, white cells and platelets in the channels that lead back to the bloodstream. At the same time, with micrometer precision, they must also hold back big molecules, such as those of albumin, but must let pass the smaller molecules of the body's waste products. If blood appears in the urine, it is a sign that the kidneys are diseased or injured. If the urine is too weak or watery, it means that the kidneys are not filtering out enough wastes.

Many things can go wrong with so complex and delicate a piece of machinery, and most kidney diseases have forbiddingly polysyllabic names. The majority of them end in -ids, meaning that the affected part of the kidney is inflamed. The others end in -osis, meaning that there is something wrong and that it is not inflammation, but beyond that the doctors are stumped.

Immune Reaction. One of the common types of kidney disease, said Cornell's Dr. David D. Thompson, is inflammation of the filtering system itself, called glomerulonephritis. Richard Bright, who died before Pasteur even suggested the microbial theory of infectious diseases, noted that many victims of this kidney disorder had recently recovered from scarlet fever. Now that scarlet fever is known to be caused by streptococci, said Dr. Thompson, physicians can predict an outbreak of nephritis after a scarlet-fever epidemic.

Just how the streptococci cause the kidney inflammation, however, is not yet known. It is not by direct infection. Likeliest explanation, said Dr. Thompson, is an immune reaction. The inflamed kidneys take weeks or months to return to normal. Children are more likely than adults to develop nephritis. But 90% of children, as against only 50% of adults, recover completely.

Perhaps the most common of all kidney infections, especially in women and children, is pyelitis--inflammation of the collecting basin in the middle of the kidney, where urine accumulates before it passes to the bladder. Since the inflammation usually involves other parts of the kidney as well, it is given the more inclusive name of pyelonephritis.

Any of several bacteria can cause pyelonephritis, but the worst offender is the colon bacillus. In women, infection is often precipitated by pregnancy; in men, by a kidney stone or prostate trouble. In many cases, pyelonephritis persists over many years. As the kidneys eventually lose their filtering efficiency, the patient may die of uremic poisoning.

Among the common forms of kidney disease that are not caused by inflammation is one that used to be called nephrosis, but is now labeled the nephrotic syndrome. Its origins are unknown, said Cornell's Dr. E. Lovell Becker, though sometimes it clearly follows an earlier kidney disease, or it is the result of an entirely different disease, such as diabetes. Even its course is impossible to predict. "The only thing certain," said Dr. Becker, "is that a fair number of these patients will go on to recover."

Any form of longstanding kidney disease results in the progressive destruction of nephrons, until there are too few left to filter the blood adequately. This is the stage traditionally known as Bright's disease, in which pyelonephritis may be indistinguishable from glomerulonephritis. Kidney diseases are so interrelated, Dr. Luckey noted, that a patient who has had any one of them is predisposed to infections that cause pyelonephritis.

Bed Rest for Some. Treatments are as varied as the forms of disease. In glomerulonephritis, a low-protein, low-salt diet, sometimes with sweet syrups and fat emulsions added, is often recommended. So is bed rest. Cortisone-type hormones do little good. Penicillin is no cure, but may be used to prevent recurrences in susceptible patients. Nephrotic syndrome patients, by contrast, usually get considerable benefit from cortisone; they, too, frequently need a low-salt diet--but with plenty of protein. And for them, bed rest is less important.

Many kidney patients drag on for years with a partial but permanent loss of filtration efficiency, punctuated by occasional flare-ups of more severe failure. At such times, they need a special diet, with a little food several times a day, and not the hospital's usual three, widely spaced meals, said Dr. Becker. Ironically some of these patients are better off if they are not put to bed, but are kept on their feet.

Only for sharply defined crises, brought on by known poisons such as carbon tetrachloride and some drugs (especially barbiturates and those containing mercury or arsenic) did the Cornell panelists recommend use of the artificial kidney. Only after all else has failed, they said, should a kidney transplant even be considered.

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