# BUN --- A **BUN** or **blood urea nitrogen** level is a lab score that gives a general idea on how your [[kidneys]] are working. It also can tell if a patient is [[dehydration|dehydrated]]. >[!science] Normal Values The normal value of BUN is **5-20 mg/dl** >>[!abstract]- Visualization >>![[metabolic panel values.png]] Elevated BUN is related more to dehydration than UTI; I won't take any points off, though, because she has s/s of upper UTI, and with potential kidney involvement there's the risk of those renal labs coming back elevated! BUN (blood urea nitrogen) and creatinine are two lab tests that are often ordered as part of a comprehensive metabolic panel. Your doctor may order this panel to get an idea of your overall health and metabolism. BUN measures the amount of urea in your blood. Urea is a waste product made in the liver as the body processes protein. This protein is mostly derived from the diet, but it can also result from tissue protein turnover [1, 2, 3]. Urea is removed by the kidneys, but the rate of removal depends on the needs of the body. The kidneys can return different amounts of urea into the bloodstream depending on factors such as hydration and blood pressure. High urea is an important marker of kidney dysfunction as well [1, 2, 3]. Creatinine, on the other hand, is a waste product created from the normal wear and tear of muscles. It is produced from creatine, a protein that helps generate energy for muscle contractions. Creatinine production essentially reflects muscle mass, and because this mass changes little from day to day, creatinine production tends to be fairly constant [3, 4, 5]. Creatinine is removed from the body by the kidneys, which filter almost all of it from the blood into the urine, at a fairly constant rate. That is why blood levels are usually a good indicator of how well your kidneys are working [3, 4, 5]. So to recap, BUN levels fluctuate, while creatinine is removed at a constant rate and its blood levels are usually stable. That’s why the BUN/Creatinine ratio can be used to check for issues such as dehydration, kidney injury/disease, gut bleeding, and other problems [3]. BUN/Creatinine Ratio Normal Range The normal range for BUN/Creatinine ratio is anywhere between 5 – 20 mg/dL. BUN/Creatinine ratio increases with age, and with decreasing muscle mass [6]. ## LOW Low BUN/Creatinine Ratio A low BUN/Creatinine ratio indicates an underlying disease/disorder and will usually be accompanied by the symptoms of this underlying disorder. The causes shown here are commonly associated with low BUN/creatinine. Work with your doctor or other health care professional for an accurate diagnosis. A BUN/Creatinine ratio lower than normal can be caused by: Low protein intake, seen in conditions of malnutrition and starvation. Less protein means lower BUN production [3]. Advanced liver disease, when the liver can’t produce enough urea, resulting in lower BUN levels [3]. Sickle cell anemia – in this condition kidneys reabsorb less urea and more of it is lost in the urine, resulting in lower BUN [3]. Hypothyroidism, a condition where the thyroid glands do not produce enough thyroid hormone. This condition can increase creatinine levels [7, 8]. Rhabdomyolysis, a condition in which damaged muscles breaks down rapidly, resulting in higher creatinine levels [3]. Kidney damage and kidney failure. When kidneys become impaired for any reason, creatinine blood levels will rise [9]. Drugs such as acetazolamide, a diuretic used to treat various conditions including glaucoma, epilepsy, altitude sickness, and heart failure [10]. ## HIGH A high BUN/Creatinine ratio indicates an underlying disease/disorder and will usually be accompanied by the symptoms of this underlying disorder. The causes shown here are commonly associated with high BUN/creatinine. Work with your doctor or other health care professional for an accurate diagnosis. A BUN/Creatinine ratio above the normal range can be caused by: Dehydration. Dehydration increases the blood levels of both BUN and creatinine but increases BUN more than creatinine [11]. Gut bleeding. The blood in the gut gets digested and this increases the amount of protein and BUN levels [12, 13]. Hyperthyroidism. This condition can increase BUN and lower creatinine levels [7]. Congestive heart failure – heart failure increases the reabsorption of urea and increases blood BUN levels [14, 15]. Kidney disease, it can increase BUN as well as creatinine levels [16]. Drugs such as tetracycline (an antibiotic) or corticosteroids (used to treat inflammation) [10, 3, 17]. ___