Creatinine and blood urea nitrogen, or BUN, are both nitrogen-containing waste products generated by muscular activity. Many patients panic if lab results come back with elevated creatinine or BUN. This is understandable because these values can be red flags for kidney disease. A single abnormal lab value should never be cause for panic, however. Creatinine and BUN can be elevated because of dehydration, drug reactions, heart disease and surgery. Video of the Day