Creatinine (CREA), Serum or Plasma

 CPT Code:  82565
 Specimen:  Serum or Plasma
 Volume:  1mL
 Minimum Volume:  0.5mL
Container: Gel-barrier tube, red-top tube, green-top (heparin) tube, or lavender-top (EDTA) tube
Methodology: Spectrophotometry (SP)
Collection: Complete clot formation should take place before centrifugation.  Serum or plasma should be physically separated from cells with a maximum limit of 2 hours from the time of collection.  Specimens should be free of particulate matter.
Reference Range: 0.43-1.13 mg/dL
  • eGFR if Non-African American: > 59 mL/min/1.73m2
  • eGFR if African American: > 59 mL/min/1.73m2

Stability

Temperatures Period
Room Temperature 1 Days
Refrigerated (2-8 ⁰C) 7 Days
 Frozen (≤ -20 ⁰C) 3 Months

            
                     
                  
                 

Use:  Creatinine, a waste product of creatine in muscles, is constantly released into the blood and excreted by the kidney. Creatinine allows a more precise evaluation of kidney function than BUN alone.

Clinical Significance:  High creatinine especially with an elevated BUN, usually indicate kidney disease. It may also indicate insufficiency with decreased glomerular filtration, urinary tract obstruction, reduced renal blood flow including congestive heart failure, shock, dehydration, or rhabdomyolysis.
 
 Low creatinine can be a cause of small stature, debilitation, or decreased muscle mass; some complex cases of severe hepatic disease can cause low serum creatinine levels. In advanced liver disease, low creatinine may result from decreased hepatic production of creatinine and inadequate dietary protein as well as reduced muscle mass

Limitations:  With reduced renal blood flow, creatinine rises less quickly than urea nitrogen. Concentration of creatinine only becomes abnormal when about half or more of the nephrons have stopped functioning in chronic progressive renal disease. Antibiotics containing cephalosporin lead to significant false-positive values if samples are drawn within four hours of a dose. With severe renal disease, creatinine is not reliable in the presence of cefoxitin therapy. There is less interference reported from the cephalosporins cephalothin, cephaloridine, cephadrine sodium, and cephaloglycin dihydrate. Lipemia, hemolysis, and bilirubin may interfere.

Causes for Rejection:  Hemolysis; improper labeling

Interfering Substances:  Bilirium (unconjugated) at 20 mg/dL and 40 mg/dL decreases a CREA result of 1.7 mg/dL by 12% at standard sample volume.
 
 Bilirium (conjugated) at 60 mg/dL decreases a CREA results of 1.7 mg/dL by 57% at standard sample volume.
 
 Lipemia interference testing at levels 600 mg/dL and greater tripped at test report message; therefore the magnitude of interference could not be determined.