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CLA: KIDNEY FUNCTION PANEL

KIDNEY FUNCTION

Normally functioning kidneys (at least one) are necessary for a healthy life. The kidney performs essential functions for the body in removing waste chemicals from metabolism of our tissue cells in producing energy, chemicals that have been detoxified by the liver (such as drugs, toxins and hemoglobin breakdown products), and has major roles in maintaining the right amount of bodily water and salts, and in regulating our blood pressure.

The kidneys can be damaged as a result of disease processes occurring elsewhere in the body, such as diabetes, infections, blood vessel diseases, high (or low) blood pressure, diseases of the blood, cancer, immune diseases such as lupus, trauma, etc. The kidneys can also have diseases of their own such as infections, structural abnormalities from birth that bring about abnormal function, cancer, and can cause high blood pressure.

Kidneys are incredibly resilient in functioning sufficiently well to keep the body alive even after great or continuing damage. When the kidneys begin to fail, the first signs are usually chemical, in the blood and urine. Consequently, periodic checking of the kidneys’ functioning, along with checking other bodily functioning, can be very beneficial in identifying problems early, when many are curable or controllable.

Metabolism of both fat and sugar eventually produces CO2, which exits the body mainly through the lungs and a small amount through the skin. However, the metabolic breakdown product of proteins, after conversion in the liver into a substance called urea, is chemically such that it must be excreted in water. Likewise, creatine in muscle is metabolized into a chemical called creatinine, which is also excreted in water. If the kidneys are not functioning properly, the concentrations of these chemicals will rise in the blood. The laboratory uses the blood urea nitrogen (BUN) and creatinine to assess kidney function, and the urinalysis to measure kidney output function and health of the collecting system (lower portion of kidney, ureters and bladder).

URINALYSIS

The urinalysis measures the presence and amount of a number of chemicals in the urine, which reflect much about the health of the kidneys, along with cells that may be present in the urine (for example, red blood cells, white blood cells, or groups of these called “casts”). Also, the lab looks for crystals, bacteria, and other organisms in the urinary sediment. Each of these elements give hints as to function of the kidneys, ureters (small tubes that connect the kidneys with the urinary bladder), and the urinary bladder.

BLOOD UREA NITROGEN (BUN)

As described above, the major breakdown product of bodily protein (e.g., in that hamburger you had for lunch) is urea, which is first formed in the liver. Urea contains nitrogen and together, in excess quantity, they are both toxic to the body and must be removed. Kidneys normally do an excellent job of removing urea, but when they start to fail, the blood concentration of urea begins to rise. The reference range (or range within which most normal people’s test values fall) for BUN is 10-20 mg/dL. Other circumstances, such as blood in the intestinal tract, a big meal of cooked meat, simple dehydration (too little water in the tissues), or any condition which decreases blood flow to the kidneys, can cause the concentration of blood urea to rise and suggest there is something wrong in kidney function. Therefore, a second blood test is done at the same time. The second blood test measures the chemical creatinine.

BLOOD CREATININE

Creatinine is a normal blood chemical that is a breakdown product of muscle metabolism. Kidneys are normally very efficient filters of creatinine. Unlike urea, the blood creatinine concentration is much less sensitive to the degree of bodily hydration, blood or meat in the intestinal tract. The reference range for blood creatinine is 0.3-1.5 mg/dL.

Considered together, the BUN, blood creatinine and their ratio give very good evidence of the filtering function of the kidneys and also, a measure of the degree of bodily hydration. The ratio of BUN: creatinine is normally 10:1. With dehydration, the ratio can increase to 20:1 or even higher. An increased BUN: creatinine ratio may also be due to certain types of kidney disease, breakdown of blood in the intestinal tract, increased dietary protein, or any clinical circumstance in which insufficient blood is flowing through the blood vessels to the kidneys (such as heart failure or kidney artery disease). The BUN: creatinine ratio is decreased in certain types of kidney disease, liver disease, malnutrition and in a condition known as Sickle Cell Anemia.

If an abnormality is found in your urinalysis, BUN, blood creatinine, or BUN: creatinine ratio, you should review these results with a physician.

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