Renal Function

Renal function is the assessment of the health and the viability of the kidneys, with a particular focus on the kidneys' ability to filter out waste products and toxins from the blood system. When the kidneys are functioning in an optimum fashion, there will generally be electrolytic balance in the body (sodium and potassium levels will be constant), and fluid levels will be balanced between blood volume and urine production by the kidneys for the excretion of wastes.

The body has two kidneys that perform equal and identical functions within the body, each located on either side of the spine; one kidney is positioned next to the liver, the other adjacent to the spleen. The adrenal glands, important in the production of the hormone adrenaline, are positioned at the top of each kidney. Humans possess an overcapacity of kidney function, in that a person may live a normal and healthy life with only one functional kidney. The kidney is an integral part of the urinary, or excretory systems, part of a continuous process that extends from the kidney to the bladder to the urethra.

Renal failure is the condition that arises when the kidney is unable to filter wastes; when this inability becomes irreversible, end stage renal failure is the consequence, which results in the need for dialysis treatment to mechanically perform the required toxin filtering. End stage renal failure will ultimately necessitate a kidney transplant, or death will result. The study of the various diseases that impact on renal function is nephrology, named for the portion of the kidney where the filtering function is carried out.

In their function as a filter, the kidneys receives all of the circulating blood within the cardiovascular system. There are a number of methods to assess whether the kidneys are adequately filtering wastes and toxins from the blood. The two most prominent of these tests are the blood urea nitrogen test, sometimes referred to as the BUN test, and analysis to determine the levels of the substance creatinine within the body. Both tests involve a chemical analysis of the person's blood.

The BUN test centers on the presence of urea in the blood stream. Urea is a compound composed of nitrogen, hydrogen, carbon, and oxygen, described by the chemical equation (NH₂)₂CO. Urea occurs in the bloodstream as waste produced by the body through the digestion of protein and its constituent amino acids. The normal range of urea in the bloodstream is well established to be between 7 mg and 25 mg/100 ml of blood. When the test reveals significant excess in the urea level, a reading in excess of 100 mg/100 ml of blood, there are three possible causes. The first is renal failure, with its very serious physical consequences.

The second possible cause of a excessive urea reading is dehydration, which occur during sport when the athlete has failed to properly hydrate either during the workout or the competition. When a person is dehydrated, the ratio of normal urea presence in the blood volume is disturbed. This condition is usually one that may be remedied through the improvement of fluid levels in the body.

The third possible cause of excess urea is the consumption of excess proteins, such as occurs with weightlifters and other strength athletes who are seeking to develop greater muscle mass and strength. As with dehydration, this condition is remedied through correction of diet. Prolonged excess protein consumption tends to place a greater strain on renal function.

Creatinine is a byproduct of the metabolism of phosphocreatine (creatine phosphate), the compound essential to the production of energy in skeletal muscles. Creatinine is a waste product that is of no use to the body once it is created, and it must be eliminated through the kidneys. As phosphocreatine is present in all skeletal muscles, and creatinine is produced at a relatively constant rate through muscular activity, creatinine levels are a reliable indicator of renal efficiency. Males have a greater amount of skeletal muscle than do females, and the normal creatinine level for men varies between 0.7 mg and 1.4 mg per 100 ml of blood; the corresponding range for women is 0.5 mg to 1.0 mg per 100 ml of blood. Readings in excess of those levels indicate an inability in the kidneys to carry out normal filtration of the blood.

The reasons for diminished renal function are many. When a kidney becomes enlarged, it will not properly function. Due to the continual exposure to the blood system and all of the potential toxins that are transported through it, the kidney is vulnerable to the development of tumors, both benign and malignant. The kidney is also vulnerable to infections that originate in the urinary tract, which may diminish its filtering capacity.

see also Diuretics; Hormones; Hydration; Sodium (salt) intake for athletes.