Creatinine
Creatinine is a byproduct in the breakdown of muscle creatine phosphate resulting from energy metabolism. It is produced at a constant rate depending on the muscle mass of the person and is removed form the body by the kidneys. Production of creatinine is constant as long as muscle mass remains constant. A disorder of kidney function reduces excretion of creatinine, resulting in increased blood creatinine levels. Thus, creatinine levels give an approximation of the glomerular filtration rate.
This test diagnoses impaired renal function. It is a more specific and sensitive indicator of kidney disease than BUN, although in chronic renal disease, both BUN and creatinine are ordered to evaluate renal problems because the BUN/creatinine ratio provides more information.
Reference Values
Normal Adult men: 0.9–1.3 mg/dL or 80–115 µmol/L Adult women: 0.6–1.1 mg/dL or 53–97 µmol/L Children (3–18 years): 0.5–1.0 mg/dL or 44–88 µmol/L Young children (0–3 years): 0.3–0.7 mg/dL or 27–62 µmol/L BUN/creatinine ratio: 10:1 to 20:1
Procedure
1.
Obtain a 5-mL venous blood sample. Serum is preferred, but heparinized blood can be used. Place specimen in a biohazard bag.
2.
Observe standard precautions.
Clinical Implications
1.
Increased blood creatinine levels occur in the following conditions:
a.
Impaired renal function
b.
Chronic nephritis
c.
Obstruction of urinary tract
d.
Muscle disease
1.
Gigantism
2.
Acromegaly
3.
Myasthenia gravis
4.
Muscular dystrophy
5.
Poliomyelitis
e.
Congestive heart failure
f.
Shock
g.
Dehydration
h.
Rhabdomyolysis
i.
Hyperthyroidism
2.
Decreased creatinine levels occur in the following conditions:
a.
Small stature
b.
Decreased muscle mass
c.
Advanced and severe liver disease
d.
Inadequate dietary protein
e.
Pregnancy (0.4–0.6 mg/dL or 36–53 µmol/L is normal; >0.8 mg/dL or >71 µmol/L is abnormal and should be noted)
3.
Increased ratio (>20:1) with normal creatinine occurs in the following conditions:
a.
Increased BUN (prerenal azotemia), heart failure, salt depletion, dehydration
b.
Catabolic states with tissue breakdown
c.
GI hemorrhage
d.
Impaired renal function plus excess protein intake, production, or tissue breakdown
4.
Increased ratio (>20:1) with elevated creatinine occurs in the following conditions:
a.
Obstruction of urinary tract
b.
Prerenal azotemia with renal disease
5.
Decreased ratio (<10:1) with decreased BUN occurs in the following conditions:
a.
Acute tubular necrosis
b.
Decreased urea synthesis as in severe liver disease or starvation
c.
Repeated dialysis
d.
SIADH
e.
Pregnancy
6.
Decreased ratio (<10:1) with increased creatinine occurs in the following conditions:
a.
Phenacemide therapy (accelerates conversion of creatine to creatinine)
b.
Rhabdomyolysis (releases muscle creatinine)
c.
Muscular patients who develop renal failure
Interfering Factors
1.
High levels of ascorbic acid and cephalosporin antibiotics can cause a falsely increased creatinine level; these agents also interfere with BUN/creatinine ratio.
2.
Drugs that influence kidney function plus other medications can cause a change in the blood creatinine level .
3.
A diet high in meat can cause increased creatinine levels.
4.
Creatinine is falsely decreased by bilirubin, glucose, histidine, and quinidine compounds.
5.
Ketoacidosis may increase serum creatinine substantially.
Clinical Alert
1.
Panic value is 10 mg/dL or 890 µmol/L in nondialysis patients.
2.
Creatinine level should always be checked before administering nephrotoxic chemotherapeutics such as methotrexate, cisplatin, cyclophosphamide, mithramycin, and semustine.
منقول
Creatinine is a byproduct in the breakdown of muscle creatine phosphate resulting from energy metabolism. It is produced at a constant rate depending on the muscle mass of the person and is removed form the body by the kidneys. Production of creatinine is constant as long as muscle mass remains constant. A disorder of kidney function reduces excretion of creatinine, resulting in increased blood creatinine levels. Thus, creatinine levels give an approximation of the glomerular filtration rate.
This test diagnoses impaired renal function. It is a more specific and sensitive indicator of kidney disease than BUN, although in chronic renal disease, both BUN and creatinine are ordered to evaluate renal problems because the BUN/creatinine ratio provides more information.
Reference Values
Normal Adult men: 0.9–1.3 mg/dL or 80–115 µmol/L Adult women: 0.6–1.1 mg/dL or 53–97 µmol/L Children (3–18 years): 0.5–1.0 mg/dL or 44–88 µmol/L Young children (0–3 years): 0.3–0.7 mg/dL or 27–62 µmol/L BUN/creatinine ratio: 10:1 to 20:1
Procedure
1.
Obtain a 5-mL venous blood sample. Serum is preferred, but heparinized blood can be used. Place specimen in a biohazard bag.
2.
Observe standard precautions.
Clinical Implications
1.
Increased blood creatinine levels occur in the following conditions:
a.
Impaired renal function
b.
Chronic nephritis
c.
Obstruction of urinary tract
d.
Muscle disease
1.
Gigantism
2.
Acromegaly
3.
Myasthenia gravis
4.
Muscular dystrophy
5.
Poliomyelitis
e.
Congestive heart failure
f.
Shock
g.
Dehydration
h.
Rhabdomyolysis
i.
Hyperthyroidism
2.
Decreased creatinine levels occur in the following conditions:
a.
Small stature
b.
Decreased muscle mass
c.
Advanced and severe liver disease
d.
Inadequate dietary protein
e.
Pregnancy (0.4–0.6 mg/dL or 36–53 µmol/L is normal; >0.8 mg/dL or >71 µmol/L is abnormal and should be noted)
3.
Increased ratio (>20:1) with normal creatinine occurs in the following conditions:
a.
Increased BUN (prerenal azotemia), heart failure, salt depletion, dehydration
b.
Catabolic states with tissue breakdown
c.
GI hemorrhage
d.
Impaired renal function plus excess protein intake, production, or tissue breakdown
4.
Increased ratio (>20:1) with elevated creatinine occurs in the following conditions:
a.
Obstruction of urinary tract
b.
Prerenal azotemia with renal disease
5.
Decreased ratio (<10:1) with decreased BUN occurs in the following conditions:
a.
Acute tubular necrosis
b.
Decreased urea synthesis as in severe liver disease or starvation
c.
Repeated dialysis
d.
SIADH
e.
Pregnancy
6.
Decreased ratio (<10:1) with increased creatinine occurs in the following conditions:
a.
Phenacemide therapy (accelerates conversion of creatine to creatinine)
b.
Rhabdomyolysis (releases muscle creatinine)
c.
Muscular patients who develop renal failure
Interfering Factors
1.
High levels of ascorbic acid and cephalosporin antibiotics can cause a falsely increased creatinine level; these agents also interfere with BUN/creatinine ratio.
2.
Drugs that influence kidney function plus other medications can cause a change in the blood creatinine level .
3.
A diet high in meat can cause increased creatinine levels.
4.
Creatinine is falsely decreased by bilirubin, glucose, histidine, and quinidine compounds.
5.
Ketoacidosis may increase serum creatinine substantially.
Clinical Alert
1.
Panic value is 10 mg/dL or 890 µmol/L in nondialysis patients.
2.
Creatinine level should always be checked before administering nephrotoxic chemotherapeutics such as methotrexate, cisplatin, cyclophosphamide, mithramycin, and semustine.
منقول
تعليق