Pharmacy Clinic
Kidney Profile
Renal function tests

Serum Creatinine
Measuring serum Creatinine is useful in evaluating any type of renal dysfunction. The term
"serum" is often used to refer to tests of substances found in the bloodstream. Serum is
the watery portion of the blood that remains after the blood is left standing long enough
for a blood clot to form. Creatinine is the waste product of creatine phosphate, a
compound found in skeletal muscle tissue. Production of Creatinine is constant as long as
muscle mass does not change significantly. Creatinine is produced at a continuous rate
and is excreted only through the kidneys. When renal dysfunction occurs, the kidneys are
impaired in their ability to excrete Creatinine and the serum Creatinine rises.

Reference values for serum Creatinine:
•        Adult males: 0.6 - 1.5 mg/dl: values are slightly higher in males due to larger
muscle mass
•        Adult females: 0.6 - 1.1 mg/dl: Creatinine clearance is increased in pregnancy,
resulting in lower serum levels
•        Children: 0.2 - 1.0 mg/dl: slight increases with age because values are proportional
to body mass
Increased serum Creatinine levels are seen in:
•        Impaired renal function
•        Chronic nephritis
•        Urinary tract obstruction
•        Muscle diseases such as gigantism, acromegaly, and myasthenia gravis
•        Congestive heart failure
•        Shock


A decrease in creatinine levels may be seen in persons with small stature, decreased
muscle mass, or inadequate dietary protein.

A panic value for creatinine is 10 mg/dl in nondialysis patients. A decreased serum
creatinine level may also indicate atrophy of muscle tissue. If muscle atrophy is suspected,
assessment of serum creatine, an important enzyme necessary for normal muscle
function, is done.

Serum creatinine is an extremely important test of renal function, as the only pathological
condition that causes a significant increase in the serum Creatinine level is damage to a
large number of nephrons.

Unlike the BUN, the serum Creatinine level is not affected by protein metabolism and by
the patient's hydration status. Tests to measure serum Creatinine, urine Creatinine, and
Creatinine clearance are all used only to evaluate renal function and only renal dysfunction
changes the results. The serum Creatinine level does not rise until at least half of the
kidney's nephrons are destroyed or damaged. Here is the relationship of Creatinine levels
to the estimated amount of nephron loss:

•        Normal Creatinine: 0.6 - 1.5 mg: up to 50% nephron loss
•        Creatinine level over 1.5 mg: over 50% nephron loss
•        Creatinine level 4.8 mg or more: up to 75% nephron loss
•        Creatinine level over 10 mg: 90% nephron loss (end-stage kidney disease)

Because creatinine levels rise and fall more slowly than BUN levels, Creatinine levels are
often preferred to monitor renal function on a long-term basis.
Creatinine clearance
Glomerular Filtration Rate

Normal Creatinine Clearance
A.        Men
1.        Average: 120 ml/min/1.73 m2 (+/-25) or 175 Liters/day
2.        Range: 97-137 ml/min/1.73 m2 (0.93-1.32 ml/sec/m2 IU)

B.        Women
1.        Average: 95 ml/min/1.73 m2 (+/-20) or 135 Liters/day
2.        Range: 88-128 ml/min/1.73 m2 (0.85-1.23 ml/sec/m2 IU)

Calculation: Cockcroft-Gault formula for GFR estimate
A.        Male GFR = (140 - age) x (weight) / (sCr x 72)
B.        Female GFR = (140 - age) x (weight) x 0.85 / (sCr x 72)

Annotation
1.        Where GFR is Glomerular Filtration Rate in ml/min
2.        Where age is in years
3.        Where weight is Lean Body Mass in kilograms
4.        Where sCr is Serum Creatinine in mg/dl

Blood Urea Nitrogen (BUN)
Blood urea nitrogen (BUN) measures the amount of urea nitrogen, a waste product of
protein metabolism, in the blood. Urea is formed by the liver and carried by the blood to
the kidneys for excretion. Because urea is cleared from the bloodstream by the kidneys, a
test measuring how much urea nitrogen remains in the blood can be used as a test of
renal function. However, there are many factors besides renal disease that can cause BUN
alterations, including protein breakdown, hydration status, and liver failure.

Reference values for BUN: (values may differ slightly from laboratory to laboratory for all
tests; the nurse should consult the laboratory manual in each agency for reference values)
•        Adult: 8-20 mg/100 ml; men may have slightly higher values than women
•        Pregnancy: values decrease about 25%
•        Newborn: values slightly lower than adult ranges
•        Elderly: values may be slightly increased due to lack of renal concentration
Increased BUN
An increase in the BUN level is known as azotemia. An elevated BUN may be caused by:
•        Impaired renal function
•        Congestive heart failure as a result of poor renal perfusion
•        Dehydration
•        Shock
•        Hemorrhage into the gastrointestinal tract
•        Acute myocardial infarction
•        Stress
•        Excessive protein intake or protein catabolism

Diseased or damaged kidneys cause an elevated BUN because the kidneys are less able to
clear urea from the bloodstream. In conditions in which renal perfusion is decreased, such
as hypovolemic shock or congestive heart failure, BUN levels rise. A patient who is
severely dehydrated may also have a high BUN due to the lack of fluid volume to excrete
waste products. Because urea is an end product of protein metabolism, a diet high in
protein, such as high-protein tube feeding, may also cause the BUN to increase. Extensive
bleeding into the gastrointestinal (GI) tract will also cause an elevated BUN because
digested blood is a source of urea. For example, a hemorrhage of one liter of blood into
the GI tract may elevate the BUN up to 40mg/dl.

Decreased BUN
A decreased BUN may be seen in:
•        Liver failure
•        Malnutrition
•        Anabolic steroid use
•        Overhydration from prolonged intravenous fluids
•        Pregnancy (due to increased plasma volume)
•        Impaired absorption (celiac disease)
•        Syndrome of inappropriate anti-diuretic secretion (SIADH)

Because urea is synthesized by the liver, severe liver failure causes a reduction of urea in
the blood. Just as dehydration may cause an elevated BUN, overhydration causes a
decreased BUN. When a person has "syndrome of inappropriate anti-diuretic secretion"
(SIADH), the anti-diuretic hormone responsible for stimulating the kidney to conserve
water causes excess water to be retained in the bloodstream rather than being excreted
into the urine. SIADH causes the BUN level, along with other important substances, to
decrease because the fluid volume of the bloodstream is significantly increased.

An assessment of the BUN is used as a gross index of glomerular function. Because the
BUN is affected by the patient's hydration status, it is a less sensitive indicator of
declining renal function than a creatinine clearance test. A BUN of over 100 mg/dl is a
panic value.