The kidneys are twin organs which filter the bloodstream to extract waste products. As the kidneys make urine, they regulate the concentration of water, sodium, potassium and the acidity (pH) of the blood stream.
Runners' Kidney (athletic pseudonephritis) involves the presence of red blood cells, proteins, and sometimes clumps of red blood cells, in the urine. When running, blood flow is shunted away from the kidneys to increase flow to the muscles. To compensate for the decreased blood flow, the kidneys increase the permeability of their filter, allowing more proteins to pass through to the urine.
Runners who develop Runners' Kidney will notice darker urine that has more of an orange tint. This usually disappears within two days.
Hematuria is intact red blood cells in the urine. It differs from Runners' Kidney in that the urine has a dark or red color. Runners should consult a doctor if the urine does not clear up after three days, to determine the cause, which could be inflammation, bruises, kidney stones, or even tumors. There are no accepted methods for preventing Runners' Kidney or Hematuria.
Acute tubular necrosis (kidney failure) is a short term damage to the tuble cells in the kidneys that make urine. After a long run, the runner's urine is dark and volume is very low or non-existant. There are three possible causes:
- Hemoglobinuria is the result of red blood cells breaking down when running on hard surfaces. The red blood cell proteins (hemoglobin) then clog up the kidneys when being filtered out of the blood stream. About 15 percent of marathon runners will have hemoglobinuria after the race.
- Myoglobinuria is the result of muscle damage, which release myoglobin (a protein) into the blood stream 24 to 48 hours after the run. Mygolobin can damage the kidneys. Dehydration increases the chances of myoglobinuria.
- Heat stroke causes dehydration, low blood pressure, and reduced blood flow to kidneys. As a result, the kidney tuble cells are deprived of oxygen.
If there is no or low urine output for hours after the long run despite drinking sufficient fluids, consult a physician. Kidney failure is a serious condition requiring medical attention. Acute tubular necrosis is reversable, but may take up to 2 weeks to recover. Runners who are prown to hemoglobinuria should wear foam rubber inserts in their shoes.