BUN stands for «blood urea nitrogen». It measures kidney function but also can be elevated in other conditions such as dehydration or internal bleeding.
Normal values vary slightly by lab but a normal BUN is generally from 5 to 25. A mildly elevated BUN (associated with a normal creatinine) usually means some measure of dehydration which would self correct within 24 hours with fluid replacement only.
A markedly elevated BUN (over 40) especially with an elevated creatinine suggests some impairment of kidney function and should be evaluated by your family physician or in an ER as soon as possible.
Creatinine is a much more sensitive and specific measure of kidney function. A normal creatinine is between 0.5 and a bit over 1.0, but not much higher than 1.2.
An elevated creatinine (especially if associated with an elevated BUN) strongly suggests impaired kidney function and should be evaluated by a physician as soon as possible.
CPK stands for creatine phosphokinase and is a measure of muscle protein breakdown. A normal CPK ranges from around 50 to almost 200.
Vigorous exercise such as a hard run or a long hike or a strenuous football practice will elevate CPK’s to 500-1000 or more with no side effects other than achy muscles. However, in prolonged extremely strenuous exercise (such as running the WSER 100), CPK’s will be elevated anywhere from a few thousand to several hundred thousand units!
The higher CPK’s will be associated with severe muscle pain, nausea, weakness, «flu-like symptoms», dark urine (Coca Cola colored) and other unpleasant symptoms. Rest and vigorous rehydration with a variety of fluids such as water, electrolyte drinks, juice, soda, etc. generally will clear the markedly elevated CPK’s within a few days.
The higher the CPK, the more likely the kidneys will become plugged up and impair kidney function. Anyone with a CPK above 40,000 should follow up with a physician within a day or two for repeat blood work. However, if the urine output is diminished or the color is not clearing or you are gaining weight or you are feeling worse as time passes instead of feeling better, you should see a physician promptly.
Sodium is an important electrolyte in your bloodstream. It is normally between 135 and 145, but occasionally can drop dangerously low during stress such as a 100 mile race. This condition is referred to as EAH or exercise associated hyponatremia.
A sodium level between 130 and 135 is mild and asymptomatic and will usually self correct with rest and normal food and fluid intake.
A sodium level of 125-130 is moderate and may or may not be associated with some symptoms such as nausea, weakness, bloating, weight gain, puffy fingers. This level is of concern and the runner should see a physician promptly for evaluation and treatment.
Severe hyponatremia is associated with a level of 120-125. Symptoms are more pronounced and may include lethargy, agitation, or confusion. This level is a medical emergency and the runner should be treated medically immediately. Levels below 120 are associated with marked alteration of consciousness, seizures, coma, and even death.
Markedly elevated levels of sodium can also be dangerous but are generally not seen in the setting of ultra running.
Potassium is an essential electrolyte located primarily inside the body’s cells. It is important for muscle function and proper heart rhythm. Normal potassium values are about 3.5 to 5.0. Potassium levels below 3.0 may cause muscle weakness and/or muscle cramps. If levels drop below 2.0, paralysis and respiratory depression may result, but these levels are very rarely seen. High potassium level (above 6.0) may affect the heart rhythm and very high levels (above 7.0) are associated with serious heart rhythm disturbances and may be fatal if not treated. Such high levels are rare in the setting of normal kidney function.