Creatinine test - Mayo Clinic
The BUN/Creatinine ratio blood test is used to diagnose acute or chronic renal (kidney) disease or damage. BUN (blood urea nitrogen) and creatinine are both filtered in the kidneys and excreted in urine. The BUN/Creatinine ratio is useful in the differential diagnosis of acute or. Your doctor should use the results of your serum creatinine test to calculate Blood Urea Nitrogen (BUN): Urea nitrogen is a normal waste. A blood urea nitrogen (BUN) test measures the amount of nitrogen in your blood that comes from the waste product urea. Urea is made when protein is broken.
In a reaction catalyzed by creatine phosphokinase CPKmost of this muscle creatine is phosphorylated to creatine phosphate.
Modified from Dosseter, Thus, creatinine production essentially reflects lean body mass. Because this mass changes little from day to day, the production rate is fairly constant. Absolute creatinine production declines with age in line with decreasing muscle mass.
Unlike urea, creatinine is largely unaffected by gastrointestinal bleeding or by catabolic factors such as fever and steroids. However, the ingestion of cooked meat can raise the sCr because cooking converts the creatine in meat to creatinine.
Certain drugs, notably the psychoactive phenacemide, can increase the production rate. Like urea, creatinine distributes throughout total body water. Its concentration in serum is a function of the usually constant production and excretion rates. It may be slightly higher in the evening than in the morning, due most likely to dietary meat intake by day. In normal subjects, creatinine is excreted primarily by the kidneys.
There is minimal extrarenal disposal or demonstrable metabolism.
Urea and creatinine concentration, the urea:creatinine ratio
As a small molecule molecular weight of daltonsit is freely filtered by the glomerulus. Unlike urea, it is not reabsorbed or affected by urine flow rate. Excretion of both urea and creatinine is increased during exercise without producing significant change in serum concentration.
The amount excreted has been used as a rough index of the completeness of daily urine collection. Measurement of urine creatinine excretion is used in calculating the creatinine clearance cCr. Short of the more precise but technically impractical inulin clearance, the cCr is the standard clinical tool for estimating GFR, especially in the early stages of renal disease.
In contrast, the cCr has the major disadvantage of inaccuracies in urine collection, especially during short-term clearances or in patients with low urine volumes. For this reason, hour clearances are preferred for general use, because the usually larger volumes will minimize errors of collection.Urea & Creatinine
The concentration of creatinine in the serum and urine is determined, and with careful attention to the units of measurement, the cCr is calculated as follows: The result may then be standardized to 1. The subject's BSA is related to weight and height and is usually obtained from a nomogram.
Several shortcuts to estimate the cCr without collecting urine have been proposed. The earliest and probably the least accurate ignores the subject's age and weight, and simply divides by the sCr. The Cockcroft-Gault formula is the one usually recommended for use in calculating dosage of drugs especially nephrotoxic antibiotics.
BUN and Creatinine - Clinical Methods - NCBI Bookshelf
It takes into account the well-documented fall in GRF with age as follows: In advanced renal failure, net creatinine excretion decreases significantly. Further, there is measurable creatinine metabolism by gut flora and, in some patients, decreased creatinine synthesis. Thus cCr is unreliable and often overestimates GFR in chronic renal failure and in cirrhosis. Certain drugs may affect cCr without changing GFR.
Salicylates, cimetidine, and trimethoprim interfere with tubular secretion of creatinine and cause a spuriously low cCr. Because they are handled primarily by glomerular filtration with little or no renal regulation or adaptation in the course of declining renal function, they essentially reflect GFR.
Unfortunately, their relation to GRF is not a straight line but rather a parabolic curve Figure Within that range, however, a doubling of the values e. Therefore, in the early stages of renal disease, these tests could create a false sense of security. A risk score to predict need for treatment for upper-gastrointestinal haemorrhage.
Lancet ; Stevenson J et tal.
Validating the Glasgow-Blatchford upper GI bleeding scoring system. Gut ; 62, 2: Cheng DW et tal. A modified Glasgow Blatchford Score improves risk stratification in upper gastrointestinal bleed: Aliment Pharmacol Ther ; 36, 8: Rahman M et tal. Am Fam Physician ; 86, 7: Pathophysiology of pre-renal azotemia. Kidney Int ; 53, 2: Agrawal M et tal.
Am Fam Physician ; 61, 7: Uchino S et tal. Clinical Kidney Journal ; 5, 2: Rachoin J et tal. The fallacy of the BUN: Nephrol Dial Transplant ; 27, 6: Beier K et tal. Crit Care Med ; 39, 2: Damman K et tal. The kidney in heart failure: Eur Heart J ; 36, Gotsman I et tal. The significance of serum urea and renal function in patients with heart failure. Medicine Baltimore ; 89, 4: Sood MM et tal. The urea-to-creatinine ratio is predictive of worsening kidney function in ambulatory heart failure patients.
J Card Fail ; 21, 5: Takaya Y et tal. Circ J ; 79, 7: Aronson D et tal. Elevated blood urea nitrogen level as a predictor of mortality in patients admitted for decompensated heart failure. Am J Med ;7: Ranson JH et tal. You can return to your usual activities immediately. In some cases, your doctor may measure the level of creatinine in your urine as well. For this test, part of a creatinine clearance test, your doctor may ask you to collect 24 hours' worth of urine in a special container and submit it for analysis.
The urine creatinine test can help your doctor more accurately assess the presence or degree of kidney failure. Results Results of the creatinine blood test are measured in milligrams per deciliter or micromoles per liter. The normal range for creatinine in the blood may be 0. Since the amount of creatinine in the blood increases with muscle mass, men usually have higher creatinine levels than do women. Generally, a high serum creatinine level means that your kidneys aren't working well.
Your creatinine level may temporarily increase if you're dehydrated, have a low blood volume, eat a large amount of meat or take certain medications.
The dietary supplement creatine can have the same effect.