• Cr
• Creat

• Red or tiger top tube
• 3-5 mL of venous blood
• Reject in case of hemolysis

• A test done as part of the basic or comprehensive metabolic panel (BMP or CMP)
• Creatinine is the breakdown product of muscle creatine phosphate
• The amount of creatinine generated in an individual is proportional to the mass of skeletal muscle present and remains fairly constant normally
• Creatinine is excreted in urine, by the kidneys
• An approximation of the glomerular filtration rate (GFR) can be calculated based upon age, gender, body weight and serum creatinine

• Creatinine levels are useful in assessing:
• Known or suspected impairment of renal function
• Known or suspected disorders involving muscles, in the absence of renal disease
• Creatinine levels increase when glomerular filtration is decreased
• Analysis of creatinine levels provides a more sensitive measure of renal damage than blood urea nitrogen (BUN) levels, however BUN and BUN/creatinine ratio may also be done to provide additional information
• BUN/Creatinine ratio is used to differentiate pre-renal, renal, and post-renal (obstructive) azotemia
• Creatinine level does not correlate well with minor or early kidney damage or disease. It may take significant (e.g. 50% of more nephrons affected) damage to result in a significant rise in creatinine.
• Creatinine has diurnal variation with higher values in the evening and night
• Day-to-day variation is 15-20%
• Serum creatinine values vary with:
• Age
• Body weight
• Gender
• Muscle mass
• Higher values are seen in men than in women
• Higher values are seen in Blacks than in Whites
• Blind persons can have higher values
• Vegetarians often have lower values

Additional information

• The BUN/creatinine ratio should be between 10:1 and 20:1.
• Creatinine level should always be checked before administering nephrotoxic agents, such as:
• Aminoglycosides
• Amphotericin
• Cisplatin
• Contrast (IV)
• Cyclophosphamide
• Methotrexate
• Mithramycin
• Semustine
• Vancomycin
• This test has been largely replaced by CPK measurements to reflect skeletal muscle necrosis and dystrophies
• Drugs and substances interfering in the spectrophotometric method include:
• 5-Fluocytosine
• Cephalosporins
• Ketones
• Lidocaine
• Related laboratory tests include:
• Anion gap
• BUN/Creatinine ratio
• Creatinine clearance
• Drug levels of
• Gentamicin
• Tobramycin
• Vancomycin
• Electrolytes (blood and urine)
• Microalbumin
• Osmolality (blood and urine)
• Urea nitrogen (blood and urine)
• Uric acid (blood and urine)
• Urine creatinine

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

Note:

A normal serum creatinine level does not rule out the presence of impaired renal function.

	Conv. Units (mg/dL)	SI Units (µmol/L)
Adult Men	0.7-1.4	62-124
Adult Women	0.5-1.1	44-97
Pregnant women	0.4-0.7	35-62
Child 3-18 yrs	0.3-1.0	27-88
Child <3 yrs	0.2-0.7	18-62
Newborn	0.3-1.0	27-88
Critical levels for a non-dialysis patient are:	10	884

BUN/Cr ratio typically 10-20:1

Elevated creatinine levels are associated with the following conditions:

• Anything that impairs renal function
• Burns
• Chronic nephritis
• Congestive heart failure
• Dehydration (Should have BUN:Cr ratio 20:1)
• Exercise (High levels)
• Hyper or Hypothyroidism
• Infections (Acute)
• Ketotic state (dieting, dehydration, diabetic)
• Leukemia
• Meat ingestion (Large amts)
• Muscle disease
• Acromegaly
• Amyotrophic lateral sclerosis
• Dermatomyositis
• Gigantism
• Muscular dystrophy
• Myasthenia gravis
• Poliomyelitis
• Obstructive uropathy
• Rhabdomyolysis
• Shock
• Systemic Lupus Erythematosus

Increased ratio BUN:Cr (20:1) with normal creatinine level occurs in the following:

• Catabolic states with tissue breakdown
• Congestive Heart failure
• Dehydration
• Gastrointestinal bleeding (Upper)
• Salt depletion
• Impaired renal function plus excess protein intake, production, or tissue breakdown

Increased ratio (>20:1) with elevated creatinine level occurs in the following conditions:

• Dehydration; Severe
• Obstructive uropathy
• Prerenal azotemia with renal disease

Drugs and substances that increase creatinine levels include:

• ACE inhibitors
• Acetaminophen (overdose)
• Acetohexamide
• Acetylsalicylic acid
• Acyclovir
• Albendazole
• Aldesleukin
• Alkaline antacids
• Alprostadil
• Altretamine
• Amiloride
• Aminoglycoside antibiotics
• Amiodarone
• Amphotericin B
• Angiotensin II Receptor Blockers
• Arginine
• Arsenicals
• Ascorbic acid
• Asparaginase
• Aspirin
• Azathioprine
• Azithromycin
• Aztreonam
• Barbiturates
• Benzodiazepines
• Beta blockers
• Bicalutamide
• Capreomycin
• Carbamazepine
• Caspofungin
• Cephalosporin antibiotics
• Cetirizine
• Chlorothiazide
• Chlorpropamide
• Chlorthalidone
• Cidofovir
• Cinoxacin
• Cisplatin
• Clarithromycin
• Clofibrate
• Clonidine
• Clorazepate
• Colistimethate
• Colistin
• Co-trimoxazole
• Cyclosporine
• Danazol
• Demeclocyclinel
• Dextran
• Disopyramide
• Diuretics
• Doxorubicin
• Doxycycline
• Enflurane
• Epoetin alfa
• Ethambutol
• Etidronate
• Etretinate
• Flucytosine
• Fludarabine
• Fluoroquinolone antibiotics
• Foscarnet
• Furosemide
• Gabapentin
• Gemcitabine
• Gemfibrozil
• Glycerin
• Griseofulvin
• Histamine-2 Blockers
• Hydralazine
• Hydrochlorothiazide
• Hydroxyurea
• Idarubicin
• Imipramine
• Immune globulin
• Interleukin alfa-2
• Isotretinoin
• Lamotrigine
• Lansoprazole
• Leuprolide
• Levodopa
• Lidocaine
• Lithium
• Lovastatin
• Mannitol
• Mefenamic acid
• Meropenem
• Mesalamine
• Methotrexate
• Methyldopa
• Methylprednisolone
• Mitomycin
• Mitoxantrone
• Moxalactam
• Mycophenolate
• Nalidixic acid
• Neomycin
• Nifedipine
• Nilutamide
• Nisoldipine
• Nitrofurantoin
• NSAIDS
• Olsalazine
• Oxaprozin
• Pamidronate
• Paromomycin
• Pegaspargase
• Penicillamine
• Penicillin Antibiotics
• Pentamidine
• Pentostatin
• Phenazopyridine
• Phosphorus
• Plicamycin
• Prednisone
• Propafenone
• Quinolone antibiotics
• Radiographic agents/IV Contrast
• Risperidone
• Salicylates
• Sargramostim
• Sevoflurane
• Streptokinase
• Streptozocin
• Sulfamethoxazole
• Sulfasalazine
• Sulfisoxazole
• Tacrolimus
• Tetracycline
• Thiazide diuretics
• Ticlopidine
• Tramadol
• Tretinoin
• Triamterene
• Trimethoprim
• Trimetrexate
• Ursodiol
• Vancomycin
• Vasopressin
• Venlafaxine
• Vitamin D

The following conditions and substances may give falsely high results:

• Acetoacetate
• Acetone
• ß-hydroxybutyrate
• Cephalosporins
• Diabetic ketoacidosis
• Glucose
• Pyruvate
• -ketoglutarate

Decreased creatinine levels occur in the following conditions:

• Advanced/Severe liver disease
• Decreased muscle mass
• Amputees
• Cachetic or elderly patients
• Inadequate dietary protein
• Small stature
• Muscular dystrophy - advanced
• Myasthenia gravis
• Pregnancy

Decreased BUN:Cr ratio (<10:1) with decreased BUN occurs in the following conditions:

• Acute tubular necrosis
• Decreased urea synthesis as in severe liver disease or starvation
• Pregnancy
• Repeated dialysis
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

Decreased BUN:Cr ratio (<10:1) with increased creatinine occurs in the following conditions:

• Muscular patients who develop renal failure
• Phenacemide therapy
• Rhabdomyolysis

Drugs that decrease serum creatinine levels include:

• Amikacin
• Ascorbic acid
• Cannabis
• Captopril
• Citrates
• Dobutamine
• Dopamine
• Ibuprofen
• Interferon -2A
• Lisinopril
• Methyldopa
• Nicardipine
• Prednisone
• Terazosin
• Triazolam
• Tromethamine
• Valproic acid
• Zidovudine

Drugs/Substances that falsely decrease serum creatinine levels include:

• Dextrose
• Histidine
• Quinidine

• LabTestsOnline®. Creatinine. [Homepage on the Internet] ©2001-2006. Last reviewed on -June 22, 2005-. Last accessed on -October 26, 2006-. Available at URL: http://www.labtestsonline.org/understanding/analytes/creatinine/test.html
• Szeto et al. Extrapolation of reciprocal creatinine plot is not reliable in predicting the onset of dialysis in patients with progressive renal insufficiency. J Intern Med. 2003 Mar; 253(3): 335-42
• Van Biesen W et al. The importance of standardization of creatinine in the implementation of guidelines and recommendations for CKD: implications for CKD management programmes. Nephrol Dial Transplant. 2006 Jan; 21(1): 77-83. Epub 2005 Oct 12.
• Walker AM et al. Anemia as a predictor of cardiovascular events in patients with elevated serum Creatinine. J Am Soc Nephrol. 2006 Aug; 17(8): 2293-8. Epub 2006 Jul 12.
• Wang X et al. Validation of Creatinine-Based Estimates of GFR When Evaluating Risk Factors in Longitudinal Studies of Kidney Disease. J Am Soc Nephrol. 2006 Sep 20; [Epub ahead of print]
• Weisbord SD et al. Associations of Increases in Serum Creatinine with Mortality and Length of Hospital Stay after Coronary Angiography. J Am Soc Nephrol. 2006 Aug 23; [Epub ahead of print]