Urea standard/serum/diluted urine 0.01 mL
Incubate at the assay temperature for 1 minute and add
Mix well and read the initial absorbance A for the
standard and test after exactly 30 seconds. Read another
absorbance A2 of the standard and test exactly 60 seconds
later. Calculate the change in absorbance ∆A for both the
Pipette into a clean dry test tube labelled Standard (S) or
Bring to assay temperature and add
Urea standard/serum/diluted urine 0.01 mL
Mix well and read the initial absorbance A1 for the
standard and test after exactly 30 seconds. Read another
absorbance A2 of the standard and test exactly 60 seconds
later. Calculate the change in absorbance ∆A for both the
Urea in mg/dL = __________ × 40 ∆A S
This procedure is linear upto 250 mg/dL. If values exceed
this limit, dilute the serum with normal saline (NaCL 0.9%)
and repeat the assay. Calculate the value using the proper
Plasma should not be collected with fluoride or heparin
salts as contamination by ammonia or ammonium salts
Reaction : Fixed time kin. Interval : 60 sec.
: 30°C/37°C Standard : 40 mg/dL
Delay time : 30 seconds React slope : Decreasing
Read time : 60 seconds Linearity : 250 mg/dL
Normal Values (general reference)
Adults: BUN is 8–18 mg%, Urea = 15–40 mg%
Adults over 60 years: May have a little higher values
normally. Low values may be found during pregnancy and
in full-term infants, whereas premature infants may have
slightly higher values than the adult range.
Common Causes of Increased BUN or Uremia
¾ Reduced blood flow to kidney
¾ Shock, blood loss, dehydration
¾ Increased protein catabolism
¾ Crush injuries, burns, fever, hemorrhage into soft tissue
¾ Glomerulonephritis, malignant hypertension, nephrotoxic drugs or metals, renal cortical necrosis
¾ Glomerulonephritis, pyelonephritis, diabetes mellitus,
arteriosclerosis, renal tubular disease, collagen-vascular
472 Concise Book of Medical Laboratory Technology: Methods and Interpretations Post-renal
¾ Ureteral destruction by stones, tumor, inflammation,
surgical trauma, obstruction of bladder neck or urethra
by prostate, stones, tumor, inflammation.
Decreased BUN is Associated with
c. Impaired absorption as in celiac disease.
d. Occasionally in nephrotic syndrome.
1. A combination of a low protein and a high carbohydrate
diet cause a decreased BUN level.
2. The BUN is normally lower in children and women
because they have a smaller muscle mass than adult
3. Increased BUN values occur in late pregnancy and
infancy because of increased use of protein.
4. Older people may have an increased BUN when their
kidneys are not able to concentrate urine adequately.
5. Decreased BUN values may normally occur earlier in
pregnancy because of physiologic hydremia.
6. Many drugs can cause increased BUN levels.
7. Drugs that may cause decreased BUN levels include
1. Ammonium oxalate should not be used as an
anticoagulant. Plasma can be used if it is obtained from
EDTA, citrate, potassium oxalate or heparin.
2. If the serum sample is very lipemic, prepare a special
blank tube by adding the phenol color reagent to
the urease before adding the serum. Set the zero
absorbance for the particular sample with this blank.
3. For urgent test__the incubation time can be reduced
to 5 minutes if the water bath temperature is raised to
4. Plasma or serum preserved with fluoride cannot be
used as this inactivates the enzyme. Urea is stable in
5. Make sure that there is no contamination by ammonia
6. For a small laboratory, commercially available multi/
Jaffe, manual method 0.8–1.5 mg/dL 70–133 µmol/day
Jaffe, kinetic or enzymatic method
Female 0.5–1.1 mg/dL 44–97 µmol/L
Males 0.6–1.2 mg/dL 53–106 µmol/L
Eldery May be lower May be lower
Cord blood 0.6–1.2 mg/dL 53–106 µmol/L
Newborn 0.8–1.4 mg/dL 71–124 µmol/L
Infant 0.7–1.7 mg/dL 62–150 µmol/L
Age 1 female ≤ 0.5 mg/dL ≤ 44 µmol/L
Age 1 male ≤ 0.6 mg/dL ≤ 53 µmol/L
Age 2–3 female ≤ 0.6 mg/dL ≤ 53 µmol/L
Age 2–3 male ≤ 0.7 mg/dL ≤ 62 µmol/L
Age 4–7 female ≤ 0.7 mg/dL ≤ 62 µmol/L
Age 4–7 male ≤ 0.8 mg/dL ≤ 71 µmol/L
Age 8–10 female ≤ 0.8 mg/dL ≤ 71 µmol/L
Age 8–10 male ≤ 0.9 mg/dL ≤ 80 µmol/L
Age 11–12 female ≤ 0.9 mg/dL ≤ 80 µmol/L
Age 11–12 male ≤ 1.0 mg/dL ≤ 88 µmol/L
Age 13–17 female ≤ 1.1 mg/dL ≤ 97 µmol/L
Age 13–17 male ≤ 1.2 mg/dL ≤ 106 µmol/L
Age 18–20 female ≤ 1.2 mg/dL ≤ 106 µmol/L
Age 18–20 male ≤ 1.3 mg/dL ≤ 115 µmol/L
Creatinine (Alkaline Picrate Method)
(Courtesy: Tulip Group of Companies)
For the determination of creatinine in serum and urine
(for in vitro diagnostic use only).
Creatinine is the catabolic product of creatinine
phosphate which is used by the skeletal muscle. The daily
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