Creatinine - CREA

This Creatinine procedure is a kinetic modification of the Jaffe procedure, in which creatinine reacts with picric acid at alkaline pH to form a yellow orange complex. However, this reaction is not completely specific for creatinine since other reducing substances such as glucose, pyruvate, ascorbic acid, and acetoacetates will react with picrate to form a similar color. Fabiny and Ertingshausen found that alkaline creatinine picrate reaches maximum color development at a different rate than pseudo-creatinine material. Cook utilized different reaction rates of alkaline picrate positive substances to obtain greater specificity with the Jaffe reaction. The rate of change in absorbance at 520/800nm is proportional to the creatinine concentration in the sample.
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Purpose and principle: 
Measurements of creatinine are used in the diagnosis and treatment of renal disease. Serum creatinine measurements prove useful in evaluation of kidney glomerular function and in monitoring renal dialysis. However, the serum level is not sensitive to early renal damage and responds more slowly than blood urea nitrogen (BUN) to hemodialysis during treatment of renal failure. Both serum creatinine and BUN are used to differentiate prerenal and postrenal (obstructive) azotemia. An increase in serum BUN without concomitant increase of serum creatinine is key to identifying prerenal azotemia. With postrenal azotemia, both serum BUN and creatinine rise, but the rise is disproportionately greater for BUN. Serum creatinine varies with the subject’s age, body weight, and sex. It is sometimes low in subjects with relatively small muscle mass, cachetic patients, amputees, and in older persons. A serum creatinine level that would usually be considered normal does not rule out the presence of impaired renal function.
Specimen Requirements: 

Type: Peripheral blood

  • Serum, gel
  • Plasma, gel

Sample Volume: 0.5mL serum

Stability (collection to time of analysis/testing):
  • Refrigerated: 7 days
  • Frozen: 1 year

Unacceptable Conditions: Moderate and gross hemolysis

Specimen Retention Time: 5 days
CPT Code (s): 

UFHPL Test #: 20140

UFHPL Epic order code: LAB66

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