BUN and creatinine levels are used to assess renal function. BUN reflects the balance between production and excretion of urea in the kidneys, and is increased in conditions that decrease renal function like acute renal failure. Creatinine is a byproduct of muscle metabolism that is excreted by the kidneys, making its level a marker of glomerular filtration rate and kidney function. Both BUN and creatinine are elevated when renal function declines and excretion decreases.

1. BUN Assists In:
Assessing renal function
Assists in diagnosing disorders such as renal failure and dehydration.
Used to assess effectiveness of hemodyalisis
1. Urea is a non-protein nitrogen compound formed in the liver from ammonia as an end
product of protein metabolism
2. Urea diffuses freely into extracellular and intracellular fluid
3. Urea is ultimately excreted by the kidneys
BUN reflects the balance between the production and excretion of urea.
BUN is Increased in:
• ARF
• CHF (due to decreased blood flow to the kidneys)
• Diabetes (related to decreased renal excretion)
• Excessive protein ingestion (related to increased protein metabolism)
• GI Bleeding (due to excessive blood protein in the GI tract and increased protein metabolism)
• Hyperalimentation (like TPN) related to increased protein metabolism
• Hypovolemia (r/t decreased blood flow to the kidneys)
BUN is Decreased in:
• Inadequate dietary intake of protein
• Low protein/High carb diet
• Malabsorption Syndrome
• Severe liver disease (BUN is synthesized in the liver, so liver damage results in decreased levels)
A patient with a grossly elevated BUN may have s/s of acidemia, agitation, confusion, fatigue, nausea,
vomiting, and coma.
Creat:
Creatinine is:
End product of creatine metabolism.
Creatine in skeletal muscle participates in energy-requiring metabolic reactions
Creatine is irreversibly converted to creatinine then circulates to the kidneys and is excreted The
amount of creatinine generated is proportional to the mass of skeletal muscle present
It remains fairly constant unless there is massive muscle damage:
• crushing injury
• degenerative muscle disease.

2. Creatinine values also decrease with age owing to diminishing muscle mass.
Blood urea nitrogen (BUN) is ordered with creatinine for comparison.
The BUN/creatinine ratio is also a useful indicator of disease.
The ratio should be between 10:1 and 20:1.
Creatinine is the ideal for determining renal clearance:
• creatinine clearance test measures a blood sample
• a urine sample to determine the rate at which the kidneys clears creatinine from the
blood; this reflects the glomerular filtration rate, or GFR
Increased in:
• Acromegaly (related to increased muscle mass)
• Congestive heart failure (related to decreased renal blood flow)
• Dehydration (related to hemoconcentration)
• Gigantism (related to increased muscle mass)
• Poliomyelitis (related to increased release from damaged muscle)
• Renal calculi (related to decreased renal excretion due to obstruction)
• Renal disease, acute and chronic renal failure (related to decreased urinary excretion)
• Rhabdomyolysis (related to increased release from damaged muscle)
• Shock (related to increased release from damaged muscle)
Decreased in:
• Decreased muscle mass (related to debilitating disease or increasing age)
• Hyperthyroidism (related to increased GFR)
• Inadequate protein intake (related to decreased muscle mass)
• Liver disease (severe) (related to fluid retention)
• Muscular dystrophy (related to decreased muscle mass)
• Pregnancy(related to increased GFR and renal clearance)
• Small stature (related to decreased muscle mass)