This article was provided in response to Bryan J Veal about ‘Bloody urine’ experienced after running.
Doctor Andrew Bosch – resident exercise physiologist
Bloody urine: Why?
Long distance runners should always keep a close watch on their urine output since it serves as a good monitoring tool for keeping a check on fluid balance, especially if training regularly in hot weather. Such observation will have revealed to the avid urine-watching runner just how long it can sometimes take before voiding for the first time after an event such as a marathon. And it will also have been noticed just how concentrated the urine can appear at that first voiding. The concentrated appearance of the urine is a little troubling to some runners. How much more so, then, if at that first voiding after a marathon the runner sees not just concentrated urine, but instead, blood.
For most runners to whom this may happen, it is quite alarming to see what appears to be a substantial amount of blood loss. This is usually followed by panic and frantic telephone calls to whomever the afflicted runner thinks may be able to help in some way. Most times, the family GP is visited the next day and various tests are done to determine the possible cause of appearance of blood in the urine. With great relief the runner then usually learns that all is well and there is no need for any treatment.
Blood in urine, or haematuria, may have a number of causes. The most common reason for haematuria is a result of impact of the walls of the bladder while running. Repeated many times over a prolonged period such as during a marathon, each of these minor impacts causes more severe damage until eventually there is sufficient trauma to cause bleeding. The damage sustained to the bladder walls can be viewed through an instrument called a cystoscope, which is how the nature of the “injury” was first determined and which has also been used to show that healing occurs within a couple of days. Since the damage is due to impact of the bladder walls, the chance of developing haematuria is greatest when running with an empty bladder. Therefore, if you develop haematuria, avoid urinating immediately before the start of a marathon and see if that helps. The presence of some urine in the bladder will help prevent the bladder walls from making contact with each other.
Another cause of haematuria may be altered permeability of the filtering apparatus. Urine is produced by filtration of the blood through a network of blood vessels surrounded by a specialised membrane, called the glomerulus. Normally, blood does not pass the glomerulus apparatus into the urine that is being formed. However, there is evidence that the permeability of the glomerulus is sometimes increased during exercise, allowing red blood cells to collect with the urine. This condition reverses once exercise stops and the problem should not persist.
A third cause of a red-coloured urine is related to haemoglobin. Haemoglobin, which is red in colour, can enter the urine under certain conditions. One such condition may occur when the red blood cells are physically damaged as they pass through the blood capillaries of the foot by impact of the feet with the ground while running. The damage sustained causes the release of the haemoglobin in the cell, which is then excreted in the urine. This phenomenon has been called “footstrike haemolysis”, or more correctly, haemoglobinuria. It does not occur very commonly. In fact, in a study by Steenkamp in 1986, there was no evidence of damage to the red cells after a marathon race. Therefore, it may only occur in susceptible people with red blood cells that are more fragile than average.
Running, however, is not the only cause of haematuria. It can also be caused by something that has nothing to do with running at all. Thus the first time that a runner experiences bloody urine after exercise a consultation with a GP is probably indicated. This is especially so if the condition does not resolve in 24 to 48 hours after exercise, if there is associated low back pain or fever, or if the bloody urine also occurs at rest. If testing reveals no apparent cause, then future episodes can be ignored. Generally, however, a runner need not be too perturbed if they pass a bloody urine after a marathon.