Creatinine Test

Creatinine Test

 

Definition

Creatine is an important compound produced by the body. It combines with phosphorus to make a high—energy phosphate compound in the body. Creatine phosphate is used in skeletal muscle contraction.

Purpose

The creatinine test is used to diagnose impaired kidney function and to determine renal (kidney) damage.

Precautions

A diet high in meat content can cause transient elevations of serum creatinine. Some drugs that may increase creatinine values include gentamicin, cimetidine, heavy-metal chemotherapeutic agents (e.g., cisplatin), and other drugs toxic to the kidneys, such as the cephalosporins.

Description

The creatinine test is used to measure the amount of creatinine in the blood. Because creatinine is a nonprotein end-product of creatine phosphate, which is used in skeletal muscle contraction, the daily production of creatine, and the following product, creatinine, depends on muscle mass, which fluctuates very little.
Creatinine is excreted entirely by the kidneys, and therefore is directly related to renal function. When the kidneys are functioning normally, the serum creatinine level should remain constant and normal. Slight increases in creatine levels can appear after meals, especially after ingestion of large quantities of meat, and some diurnal variation may occur, with a low point at 7 A.M. and a peak at 7 P.M. Serious renal disorders, such as glomerulonephritis, pyelonephritis, and urinary obstruction, will cause abnormal elevations.
The creatinine level is interpreted in conjunction with another kidney function test called the Blood Urea Nitrogen (BUN). The serum creatinine level has much the same significance as the BUN but tends to rise later. Because of this, determinations of creatinine help to chronicle a disease process. Generally, a doubling of creatinine suggests a 50% reduction in kidney filtration rate.

Preparation

The creatinine test requires a blood sample. It is recommended that the patient be fasting (nothing to eat or drink) for at least eight hours before the test. The physician may also require that ascorbic acid (vitamin C), barbiturates, and diuretics be withheld for 24 hours.

Risks

Risks for this test are minimal, but may include slight bleeding from the blood-drawing site, fainting or feeling lightheaded after venipuncture, or hematoma (blood accumulating under the puncture site).

Normal results

Normal values can vary from laboratory to laboratory, but are generally in the following ranges:
  • Adult female: 0.5-1.1 mg/dL
  • Adult male: 0.6-1.2 mg/dL
  • Adolescent: 0.5-1.0 mg/dL
  • Child: 0.3-0.7 mg/dL
  • Infant: 0.2-0.4 mg/dL
  • Newborn: 0.3-1.2 mg/dL.

Key terms

Glomerulonephritis — Glomerulonephritis is an inflammation of the filtering units of the kidney (glomeruli). The condition hinders removal of waste products, salt, and water from the bloodstream, leading to serious complications. It is the most common cause of renal failure.
Pyelonephritis — Pyelonephritis is an inflammation of the kidney itself, usually caused by a bacterial infection. In its most serious form, complications can include high blood pressure (hypertension) and renal failure.
Note that variations between sources for serum creatinine normal ranges are greater than for other important tests. For example, due to the greater amount of muscle mass generally present, males normally demonstrate higher creatinine levels than females. Also, because the kidney filtration rate normally increases in pregnancy, serum creatinine should be slightly less during such periods. In older patients, creatinine is reduced because of decreased muscle mass. Similarly, other patients may have creatinine levels in which muscle abnormalities must be taken into consideration, such as long-term corticosteroid therapy, high thyroid (hyperthyroidism), muscular dystrophy, or paralysis.

Abnormal results

Two to 4 mg/dL indicate the presence of impairment of renal function. Greater than 4 mg/dL indicates serious impairment in renal function.

Resources

Books

Pagana, Kathleen Deska. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby, Inc., 1998.
References in periodicals archive ?
A urine creatinine test is by itself not a reliable indicator of kidney function.
DekPHAN Laura and MicroAlbuPHAN Laura are routine 10 parameters and 2 parameters specialized Microalbumin and Creatinine test strips respectively .
A POC creatinine test that predicts a patient's risk for contrast-induced nephropathy and is carried out in 10 min in the emergency room prior to radiologic imaging trumps (as long as it is "good enough") a central-laboratory test that takes 30 min (or longer) to reach the caregivers (2).
As the samples from the original CG study were no longer available for re-analysis using IDMS-standardised creatinine assays there is a possibility that dosing guidelines may be incorrect when using standardised creatinine test results.
2], who received treatment in the medical ward for at least 1 day after a serum creatinine test was performed.
The difference in creatinine values between IDMS and non-IDMS methods, along with normal ranges, makes eGFR testing an ongoing situation that requires good communication between the laboratory and caregivers who utilize creatinine test results.
The doctor said he would have to order a creatinine test to be done before scheduling the scan.
In addition, creatinine levels can fluctuate with age, race, sex, or body mass, therefore complicating the meaning of creatinine test results.
Urinary creatinine levels were determined using a creatinine test kit (Wako Pure Chemical Industries, Osaka, Japan).
As a result, the number of coronary heart disease patients able to get lipid-lowering prescriptions has increased from 58% to 95%; the number of hypertensive patients with well-controlled blood pressure has increased from 45% to 84%; and the number of diabetes patients undergoing the microalbumin / creatinine test to evaluate kidney function has increased from 4% to 85%.
Because small changes in creatinine can result in significant changes to eGFR, some laboratory experts have cautioned that bias and interference in current laboratory creatinine test methods may limit the ability to accurately report GFR.
This indicates a need to check kidney function with a serum creatinine test.