I have two questions: My mother’s friend was told his kidneys are weak. What can he do for that? My wife is losing protein through her urine at the rate of almost 3000 mg/day. How dangerous is that?
Both questions deal with kidney disease, and although I don’t know the specifics about either case, I thought it would be a good jumping off point for a general discussion of kidney, or renal disease.
When doctors tell someone that one of their organs is weak, it’s usually a euphemism for failing. In heart failure, the heart is unable to pump as strongly as possible, it is weak and it starts to fail. In liver failure, the organ can no longer carry out its important metabolic functions, and it fails.
The kidneys are similar, they carry out a number of crucial functions and when they fail a person’s survival is threatened. Fortunately, for people with kidney failure, we have renal dialysis which can keep them alive indefinitely. There is no comparable replacement technology for the heart or the liver, although implantable heart replacements may not be too far in the future.
So what are the important metabolic functions that the kidneys perform, and what happens when they start to fail? There are quite a few, but I’ll try to list the most important:
- The kidneys regulate the amount of water in the body. Everyone knows that if you drink more you urinate more, but the opposite is equally important, if you drink less, or lose more fluid, (by sweating for example), the kidneys put out less urine.
- The kidneys also regulate the amount of salt, and some other chemicals, in the body. In hot dry climates, or in endurance athletes, the kidneys accommodate by restricting salt loss in the urine. Although salt has received a bad rap in recent years, it’s a crucial compound for maintaining blood pressure and proper fluid balance in the body.
- The kidneys are crucial in excreting the waste products of protein breakdown, specifically the nitrogen products of that metabolism. Amino acids, the building blocks of proteins, all carry an amine group, chemically written as -NH2. As proteins are broken down and their components recycled, amine groups would build up if there were not some way to excrete them, and we do so by making them into urea. This is excreted in the urine, and one of the major ways that we judge the degree of renal failure is by measuring the amount of urea, (and creatinine, another compound carrying an amine group) that is present in the blood. As renal failure progresses, these compounds build up in the blood, and provide a useful way of measuring the severity of the failure.
How does the kidney do all this? It’s actually unbelievably complicated. We all have two kidneys, an insurance policy since one can be lost and the person will survive. Each is made up of millions of tiny units called nephrons. Each nephron consists of a glomerulus, a tiny ball of capillaries covered by a special membrane, and an elaborately coiled tubule, which eventually leads the urine produced down into the ureters and the bladder. The glomerulus filters the blood, allowing water and tiny molecules to pass into the stream that will become urine. We filter about 180 liters a day, but we only urinate on the average 1.5 liters per day. All the rest is absorbed by the tubules, while various adjustments are made to the chemicals that were filtered, some are reabsorbed, others are secreted. In this way the amount of water, salt and other chemicals are kept at normal levels in the body, and waste products like urea are excreted.
Your mother’s friend who has weak kidneys is probably showing a buildup of urea and creatinine in his blood. Appropriate treatment will depend on what’s causing the failure. If it is diabetes, the commonest cause of renal failure in the United States, then treatment will consist of very close control of the blood sugar, and the addition of an ACE inhibitor type drug, which has been shown to slow the progression of renal failure. If he is also hypertensive, then control of the blood pressure, not just to within high normal levels but down to mid or low normal levels, like 120/70, will slow the progression of kidney failure. If the failure has become severe, then protein restriction will be important to lower the amount of those amine groups entering his body. At some point dialysis may become necessary.
Your wife also has serious kidney disease. Many conditions could cause this amount of protein loss in the urine, but again the most common is diabetes. This amount of protein loss damages the glomeruli, and will lead to progressive renal failure. If it is due to diabetes, tight control and an ACE inhibitor will be crucial in reducing the deterioration of her renal function.