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Creatinine Clearence

The kidney is the great eliminator of the body.

Test Indications:

  • Assessment of kidney (renal) function.
  • Assessment of need for protein restriction in renal patients
  • Suspected kidney insufficiency or kidney disease.
  • Assessment of kidney function prior to chelation therapy

Test Summary:

  • Test measures creatinine clearance in the urine

Measuring Kidney Function

The creatinine clearance test is a convenient means of assessing kidney function. Toxic metals and xenobiotics (including some pharmaceutical agents) are damaging to kidney tissue and can decrease efficiency of kidney filtration. The kidney filters through a mesh-like structure called the glomerulus through a process called glomerular filtration. Efficient glomerular filtration is critical during chelation therapy in which there is increased mobilization of toxic elements resulting in elevated demands on renal clearance. Assessment is highly recommended for determination of the appropriate dose of a chelating agent for an individual patient and for weighing the advisability of prescribing a variety of drugs.

Creatinine is a breakdown product of creatine, which is an important part of muscle. Creatinine is a substance neither secreted nor reabsorbed by renal tubules, thus urine creatinine can be used to measure renal function through assessment of glomerular filtration. Creatinine excretion is independent of urine flow, and the plasma concentration of creatinine is relatively constant. Therefore, the rate of creatinine clearance can be determined by analyses of creatinine in a 24-hour urine collection and a single blood specimen that has been collected during that same 24-hour period.

The quantity of creatinine formed in the body is related to muscle mass and does not change significantly with dietary variability. Heavy metals such as mercury, cadmium and lead are potent nephrotoxins which can markedly decrease renal function and result in increased levels of toxic substances in the body. Safe chelation therapy is highly dependent upon the adequacy of renal function. Excessive mobilization of toxic metals to poorly functioning kidneys can exacerbate kidney damage. Therefore, it is highly recommended that the rate of creatinine clearance be measured in order to determine the appropriate dosage of a chelating agent for each individual patient. Periodic reassessment of the clearance rate is also recommended and can serve to monitor therapeutic effectiveness.

Pharmaceutical agents such as some antihypertensive agents should be prescribed with caution, especially in patients with marginal kidney function. Determination of creatinine clearance is therefore appropriate before placing patients on certain therapeutic regimens. Assessment of renal function is also warranted for patients with known renal disease or for those at risk for renal dysfunction. For renal patients, the rate of creatinine clearance indicates whether dietary protein restriction is warranted.

Reference ranges are provided for individuals of normal weight for height. The clearance rate corrected for body surface area in square meters can also be calculated.

It is essential that the blood specimen be drawn sometime during the 24-hour urine collection period. To facilitate compliance and accuracy of test results, detailed patient instructions are provided with the test kit.