Serum creatinine is the concentration of a compound known as creatinine in the blood or urine. It is tested during routine metabolic panels, usually with the goal of evaluating a patient who may be at risk for kidney disease. Most labs have the ability to check serum creatinine, often providing same day turnaround service with rapid results.
The serum creatinine test can be recommended as part of a comprehensive panel of a patient or as a standalone test because there are specific concerns. When a doctor recommends this diagnostic test, patients may want to ask why it is being recommended, what the possible results are, and how long it will take to receive results.
Creatinine is a waste product produced by the body at a relatively stable rate. It is a byproduct of the cycle used to deliver energy to the muscles. The kidneys are responsible for clearing creatinine from the body and when they are not functioning properly, more of this compound starts to circulate in the blood. In the early stages of a kidney problem the levels may be within normal range, but eventually they will rise high enough to indicate that the kidneys are not working.
People can also have high serum creatinine in pregnancy or in the wake of a muscle injury in some cases. Patients with high test results may be evaluated to rule out these possibilities. A doctor would expect to see high levels in patients with kidney failure, kidney cancers, and diseases of the cardiovascular system.
This test is relatively low cost, making it appealing to a doctor who wants to work a patient up quickly to rule out possibilities without expending a lot of money or exposing the patient to invasive tests. Once serum creatinine is determined, a lab technician can use the information to generate a creatinine clearance value, taking the patient's age, height, weight, and gender into account. This value can provide even more information about kidney function.
One problem with the serum creatinine test is that people can be experiencing kidney disease and the start of kidney damage while the values still fall within normal range. Other values on a metabolic panel can provide additional information about kidney function. Once the kidneys start to function abnormally, it is common to see other changes in a blood profile because the kidneys are not able to express a wide variety of waste products.
BUN-creatinine ratio is used to determine the cause of sudden dysfunction of kidney or acute renal failure. Read on to know about normal, low and elevated BUN and creatinine levels.
Urea and creatinine are nitrogenous end products of body metabolism. Urea is generated from dietary protein and tissue protein turnover. Muscle creatine catabolism generates creatinine. In Europe, the whole urea molecule is taken into consideration while in the United States, only the nitrogen component of urea (the blood urea nitrogen or serum urea nitrogen, i.e., BUN or SUN) is measured. The BUN is roughly one-half (28/60 or 0.446) of the blood urea. Before taking a look at BUN and creatinine levels, let us take a look at the uses of BUN-creatinine ratio.
BUN to creatinine ratio is the ratio of blood urea nitrogen to serum creatinine. Creatinine is a break-down product of creatine phosphate in muscle. It is usually produced at a constant rate by the body but it can vary according to the muscle mass. Men have more muscle mass than women and hence tend to have higher levels of creatinine than women. Vegetarians usually have low creatinine levels. Kidneys play an important role in filtration of creatinine or removal of creatinine from the blood. When kidneys do not filter the blood properly, elevated creatinine levels are noticed. If more or complete estimation of renal function is to be done, then the blood (plasma) concentration of creatinine along with that of urea has to be taken into consideration. BUN and creatinine levels help detect other problems besides those related to the kidney. For instance, a disproportionate rise in urea level when compared with the creatinine may indicate a pre-renal problem such as volume depletion. BUN and creatinine levels in blood and urine can help you calculate the creatinine clearance, which reflects the glomerular filtration rate (GFR). Glomeruli are the small capillaries which filter the blood during urine formation. The GFR is clinically important as renal function can be assessed with the help of GFR.
The normal range of urea nitrogen in blood is around 5 to 20 mg/dl or 1.8 to 7.1 mmol urea per liter. The range is wide pertaining to normal variations due to protein intake, endogenous protein catabolism, state of hydration, hepatic urea synthesis and renal urea excretion. For example, a BUN of 15 mg/dl would indicate 'significantly affected function' for a woman in the third trimester of pregnancy whereas a rancher who consumes 125 g of excess protein each day may have a normal BUN of 20 mg/dl. The pregnant woman's higher glomerular filtration rate (GFR), expanded extracellular fluid volume and anabolism in the developing fetus are responsible for her relatively low BUN of 5 to 7 mg/dl.
An elevated BUN can occur in case of diabetes, congestive heart failure, gastrointestinal bleeding (GI), dehydration, kidney dysfunction, hypertension, etc. Dry-itchy skin, insomnia, nausea, fatigue, etc. are some of the commonly noticed elevated BUN symptoms.
The normal serum creatinine (Cr) may vary according to the person's body muscle mass and the methods used to measure it. For the adult male, the normal creatinine levels range from 0.6 to 1.2 mg/dl, or from 53 to 106 μmol/L by the kinetic or enzymatic method and 0.8 to 1.5 mg/dl, or 70 to 133 μmol/L by the older manual Jaffé reaction. For an adult female, the normal creatinine levels in blood ranges from 0.5 to 1.1 mg/dl, or from 44 to 97 μmol/L by the enzymatic method.
The normal BUN and creatinine levels should show a ratio of 10:1 to 20:1, if the age of the patient is more than twelve months. The normal bun and creatinine levels ratio can be around 30:1 in case of babies, younger than twelve months. The normal BUN values should be 5-15 mg/dL for children, 8-23 mg/dL for the adults and 5-12 mg/dL during pregnancy.
A BUN-creatinine ratio greater than 20:1, is referred to as elevated BUN and creatinine levels which can be observed due to decreased glomerular filtration rate (GFR). Low BUN creatinine levels, where the BUN-creatinine ratio is less than 10:1, indicates reduced reabsorption of BUN due to renal damage. Owing to the decreased muscle mass, elderly patients may have an elevated BUN:Cr ratio at baseline.
Low BUN creatinine levels indicate inadequate protein intake, reduced urea synthesis as in advanced liver disease, excessive excretion of urea as in sickle cell anemia, increased creatinine production as in rhabdomyolysis or more effective removal of urea than creatinine, during dialysis.
The external factors affecting BUN and creatinine levels are high protein intake, gastrointestinal bleeding, fever, burns, excessive use of steroids, starvation, malnutrition, urinary tract obstruction, dehydration, etc. Regular BUN and creatinine levels checkup can help monitor the functioning of kidneys and other organs.