BUN : Semi quantitative blood urea nitrogen
determination of blood urea nitrogen is an important index of kidney function.
The VET-BUN Reagent Test Strips by Teco provide a quick, convenient way way to
semi-quantitatively approximate blood urea nitrogen levels in whole blood.
B.u.n. Reagent Strips
treatment applies to the following species:
Reagent Strips are a reagent strip for the determination of blood urea
nitrogen. A semi-permeable membrane is employed. Each strip is stable and
ready to use when removed from the storage vial.
- B.U.N. Reagent
Reagent Strips are a one minute test for blood urea nitrogen in whole blood,
serum or heparinized plasma.
Collection and Preparation: B.U.N. Reagent strips are intended for use with
whole blood, serum or heparinized plasma only.
1. Range: 10-100 mg/dl
2. Specimen: whole blood, serum or heparinized plasma
3. Sample Volume: 50-100 µL (1 drop)
4. Reaction Time: 1 minute
5. Storage: room temperature only
blood with fluoride as a preservative should be avoided. Hematocrits greater
55% can cause lower results.
If patient is severely dehydrated use serum or plasma only.
Value for B.U.N.:
Canine: 10-20 mg/dl
Feline: 10-30 mg/dl
Equine: 10-25 mg/dl
timing is critical for this technique.
1. Apply 1 large drop (50-100 µL) of sample to the pad.
2. Wait 30 seconds.
Wipe sample off with a tissue. Use moderate pressure evenly on the reagent pad
all excess sample.
4. Wait an additional 30 seconds.
5. Compare color of the pad with the color chart to obtain B.U.N. value.
strips should be stored in the vial in a cool, dry place at room temperature.
Avoid excessive humidity, temperature extremes, and direct sunlight. The vial
should be stored tightly capped with the desiccant. Remove desired number of
strips and recap immediately. Do not handle reagent pad area. Do not
- B.U.N. Reagent Strips Caution(s)
Reagent strips are for in-vitro diagnostic use.
Reagent strips are available in kits of 25 tests.
VET 10 : Ascorbic acid
Specific gravity (Sp.gr.)
VET-BUN whole blood Test strip
VET-BUN in milk Test strip
VET-BHB in milk Test strip
Urea Nitrogen (BUN) Concentration in Dogs
Jennifer A. McKee, DVM; Kenneth S. Latimer, DVM, PhD; Bruce E.
LeRoy, DVM, PhD
Class of 2004 (McKee), Department of Pathology (Latimer, LeRoy),
The blood urea nitrogen (BUN) test is a measurement of the amount
of urea that has been passively absorbed into the vascular system. The
majority of urea (Fig. 1) is synthesized from ammonia by the liver during the
hepatic urea cycle.2 Urea is freely filtered by the glomeruli and
partially passively resorbed as filtrate transverses the renal tubules.5 The
kidneys excrete the majority of urea. Reabsorption of urea is inversely
related to urine flow rate, as well as many other factors.
Figure 1. Molecular structure of urea (H2NCONH2).
In the past, BUN was measured in whole blood. Today, BUN
concentration is determined by analysis of serum or plasma.5 Blood
urea nitrogen, serum urea nitrogen, and urea nitrogen measurements are
equivalent due to the fact that urea diffuses quickly and passively through
the total body water compartment (diffusion time of approximately 90 minutes).2
Blood urea nitrogen is most accurately measured by a colorimetric
process, which gives a quantitative test result.2 It can also be
measured by the diacetylmonoxime method, but the test results are less
accurate. The reference interval for BUN in the dog ranges from 8 to 28 mg/dl.2
Importance of Measuring BUN
Blood urea nitrogen (BUN) is typically measured to assess kidney
function; however, there are many different metabolic processes and diseases
that alter BUN concentration.
The processes that alter BUN can be broken into three major
categories including pre-renal, renal, and post-renal abnormalities (Table 1).1,2
BUN is often considered an insensitive measure of kidney function
since an increase in BUN concentration occurs only after at least 65%-75% of
the functional kidney mass has been lost (Fig. 2).4 Measuring the
urine specific gravity can help differentiate between pre-renal and renal
causes of azotemia (increased concentration of urea or other nonprotein
nitrogen compounds in the blood). In pre-renal azotemia, renal function is not
altered. The kidneys are able to concentrate urine, resulting in a urine
specific gravity of >
dogs and >
cats. With renal azotemia the urine specific gravity will be lower than these
values, and may be isosthenuric (1.008-1.012) because the kidneys have lost
the ability to concentrate the urine. Creatinine is another nitrogenous
substance in the blood whose measurement also may assist in differentiating
the causes of azotemia.
Figure 2. Longitudinal cut sections of a kidney (left) from a dog with end
stage renal disease compared to a normal kidney (right). The diseased
kidney has an undulating surface, variable width of the cortex, and a
lighter color. The normal kidney has a smooth surface, regular
cortical width, and a dark mahogany color (Courtesy of Noah's Arkive,
The University of Georgia).
Table 1. Major causes of increased and decreased blood urea nitrogen
catabolism of protein
fluid intake and increased fluid output
growth-increased anabolic state
of functional kidney mass
(systemic lupus erythematosus)
or leakage into peritoneal cavity
for Increased BUN Concentration
Upper gastrointestinal hemorrhage - Increased BUN concentration due to upper gastrointestinal tract
hemorrhage is thought to be caused by increased protein catabolism as well as
blood volume loss.3 A retrospective study by Prause et. al. determined that patients with clinical signs of upper
gastrointestinal tract hemorrhage had significantly increased BUN
concentration and BUN/creatinine ratio.
Post renal obstruction - Vasoactive substances such as prostaglandins and angiotensin are
released during obstruction of the urinary system. These substances cause
constriction of the glomerular arterioles, reducing the blood flow and
decreasing the glomerular filtration rate (GFR). In turn, the decreased GFR
prevents clearance of both BUN and creatinine, causing increased
concentrations of these substances in the blood.4
Mechanisms for Decreased BUN Concentration
The basic mechanism causing a decreased BUN concentration is a
decrease in protein catabolism or an inability to synthesize urea from
Hepatic insufficiency - Hepatic insufficiency causes a decreased BUN concentration due
to destruction of functional hepatic mass and decreased urea output from the
hepatic urea cycle.2
BUN concentration is most often measured to assess kidney function.
It is important to realize that many different disease conditions alter BUN
concentration but may or may not alter renal function. Therefore, BUN
concentration should be compared with creatinine concentration and urine
specific gravity to properly evaluate kidney function.
1. Finco DR
: Kidney function. In: Kaneko JJ, Harvey JW, Bruss ML (eds):
Clinical Biochemsitry of Domestic Animals, 5th ed. San Diego, Academic Press,
1997, pp. 468-472.
2. Gregory CR: Urinary System. In:
, Mahaffey EA, Prasse KW: Duncan and Prasses Veterinary Laboratory
Medicine: Clinical Pathology, 4th ed.
, Iowa State Press, 2003, pp 250-53 & 341.
3. Prause LC, Grauer GF: Association of gastrointestinal hemorrhage
with increased blood urea nitrogen and BUN / creatinine ratio in dogs: A
literature review and retrospective study. Vet Clin Pathol 27:107-110, 1998.
4. Stockham SL, Scott MA: Fundamentals of Veterinary Clinical
State Press, 2002, pp. 289-294.
5. Osborne CA,
(eds): Canine and Feline Nephrology and Urology. Baltimore, Williams &
Wilkins, 1995, pp. 217-218.
The image of the urea molecular model above (background slightly
modified) is from the web site of Dr. Suzanne W. Slayden, Chemistry