High blood creatinine with low urea nitrogen may be caused by various factors such as strenuous exercise, nephritis, renal failure, etc. The specific situation requires further medical examination and evaluation and judgment by professional doctors. 1. Strenuous exercise: Generally after strenuous exercise, due to muscle metabolism enhancement, blood creatinine usually increases. After a short rest, the blood creatinine will return to normal. 2. Nephritis: usually due to immune system disorders, bacterial infections and other factors lead to glomerulonephritis, and nephritis makes the glomerular filtration function reduced, which leads to high blood creatinine accompanied by urea nitrogen not high. 3. Renal failure: it may be due to trauma or burns and other factors leading to renal failure, at this time the glomerular filtration capacity decreases, and there may be elevated blood creatinine concentration with low urea nitrogen. If there is a high blood creatinine with urea nitrogen is not high, to control the protein intake, at the same time should go to the hospital in time for examination, to clarify the cause of the disease, under the guidance of physicians for standardized treatment.