Clinical Chemistry 481

Causes of Monoclonal Gammopathies

¾ Multiple myeloma

¾ Waldenstrom’s macroglobulinemia

¾ Benign idiopathic monoclonal gammopathy

¾ Heavy chain diseases

¾ Collagen disorders, autoimmune diseases

¾ Certain lymphomas

¾ Cirrhosis liver

¾ Neoplasms of colon, prostate, breast, female genital

tract, stomach and lungs

¾ Myeloproliferative disorders-CML, polycythemia,

myelofibrosis, erythrimic myelosis, erythroleukemia,

other acute leukemias

¾ Aberrations in lipid metabolism

¾ Diabetes mellitus.

Interfering Factors

1. Low levels of albumin occur normally in all trimester’s

of pregnancy.

2. Bromosulfalein may cause a false elevation. Therefore,

a serum protein test should not be done within 48 hours

following a BSP test.

3. See appendix for complete listing of drugs that

interfere with total protein levels.

SERUM CHOLESTEROL

Cholesterol (CHOD/PAP Method)

(Courtesy: Tulip Group of Companies)

For the determination of cholesterol in serum or plasma

(for in vitro diagnostic use only).

Summary

Cholesterol is the main lipid found in blood, bile and brain

tissues. It is the main lipid associated with arteriosclerotic

vascular diseases. It is required for the formation of

steroids and cellular membranes. The liver metabolizes

the cholesterol and it is transported in the blood

stream by lipoproteins. Increased levels are found in

hypercholesterolemia, hyperlipidemia, hypothyroidism,

uncontrolled diabetes, nephrotic syndrome, and cirrhosis.

Decreased levels are found in malabsorption, malnutrition, hyperthyroidism, anemias and liver diseases.

Principle

Cholesterol esterase hydrolyzes esterified cholesterols to

free cholesterol. The free cholesterol is oxidised to form

hydrogen peroxide which further reacts with phenol and

4-aminoantipyrine by the catalytic action of peroxidase to

form a red colored quinoneimine dye complex. Intensity

of the color formed is directly proportional to the amount

of cholesterol present in the sample.

 Cholesterol esterase

Cholesterol esters + H2O Cholesterol + Fatty acids

 Cholesterol oxidase

Cholesterol + O2 Cholestenone + H2O2

 Peroxidase

H2O2 + 4 Aminoantipyrine + Phenol Red

quinoneimine

dye + H2O

Normal Reference Values

Serum/plasma (Suspicious) : 220 mg/dL and above

(Elevated) : 260 mg/dL and above

It is recommended that each laboratory establish its

own normal range representing its patient population.

Contents 2 × 75 mL 2 × 150 mL

L1: Enzyme reagent 1 2 × 60 mL 2 × 120 mL

L2: Enzyme reagent 2 2 ×15 mL 2 × 30 mL

S: Cholesterol standard (200 mg/dL) 5 mL 5 mL

Storage/Stability

Contents are stable at 2–8°C till the expiry mentioned on

the labels.

Reagent Preparation

Reagents are ready to use.

Working reagent: Pour the contents of 1 bottle of L2

(Enzyme reagent 2) into 1 bottle of L1 (Enzyme reagent

1). This working reagent is stable for at least 8 weeks when

stored at 2–8°C. Upon storage the working reagent may

develop a slight pink color however, this does not affect the

performance of the reagent. Alternatively for flexibility as

much of working reagent may be made as and when desired

by mixing together 4 parts of L1 (Enzyme reagent 1) and

1 part of L2 (Enzyme reagent 2). Alternatively 0.8 mL of L1

and 0.2 mL of L2 may also be used instead of 1 mL of the

working reagent directly during the assay.

Sample Material

Serum, EDTA plasma. Cholesterol is reported to be stable

in the sample for 7 days when stored at 2–8°C. The sample

should preferably be of 12 to 14 hours fasting.

482 Concise Book of Medical Laboratory Technology: Methods and Interpretations Procedure

Wavelength/filter : 505 nm (Hg 546 nm)/green

Temperature : 37°C/RT

Light path : 1 cm

Pipette into clean dry test tubes labeled as blank (B),

standard (S), and test (T):

Addition

Sequence

B

(mL)

S

(mL)

T

(mL)

Working reagent 1.0 1.0 1.0

Distilled water 0.01 - -

Cholesterol standard (S) - 0.01

Sample - - 0.01

Mix well and incubate at 37°C for 5 minutes or at RT (25°C)

for 15 minutes. Measure the absorbance of the standard

(Abs S), and test sample (Abs T) against the blank, within

60 minutes.

Calculations

 Abs T

Cholesterol in mg/dL = ________ × 200 Abs S

Linearity

This procedure is linear upto 750 mg/dL. If the value

exceeds this limit, dilute the serum with normal saline

(NaCL 0.9%) and repeat the assay. Calculate the value

using the proper dilution factor.

Note

Anticoagulants such as fluorides and oxalates result in

false low values. The test is not influenced by Hb values

upto 20 mg/dL and bilirubin upto 10 mg/dL.

System Parameters

Reaction : End point Interval : ...

Wavelength : 505 nm Sample

volume

: 0.01 mL

Zero setting :  Reagent blank Reagent

volume

: 1.00 mL

Incubation

temperature

: 37°C / RT Standard : 200 mg/dL

Incubated

time

: 5 min/15 min Factor :

Delay time : — React slope : Increasing

Read time : — Linearity : 750 mg/dL

No. of read : — Units : mg/dL

Normal values

Male Female

SI units SI units

Age mg/L mmol/L mg/dL mmol/L

Total cholesterol

Adult

20–24 124–218 3.21–5.64 122–216 3.16–5.59

25–29 133–244 3.44–6.32 128–222 3.32–5.75

30–34 138–254 3.57–6.58 130–230 3.37–5.96

35–39 146–270 3.78–6.99 140–242 3.63–6.27

40–44 151–268 3.91–6.94 147–252 3.81–6.53

45–49 158–276 4.09–7.15 152–265 3.94–6.86

50–54 158–277 4.09–7.17 162–285 4.20–7.38

55–59 156–276 4.04–7.15 172–300 4.45–7.77

60–64 159–276 4.12–7.15 172–297 4.45–7.69

65–69 158–274 4.09–7.10 171–303 4.43–7.85

> 70 144–265 3.73–6.86 173–280 4.48–7.25

Child

Cord blood 44–103 1.14–2.66 50–108 1.29–2.79

< 4 114–203 2.95–5.25 112–200 2.90–5.18

5–9 121–203 3.13–5.25 126–205 3.26–5.30

10–14 119–202 3.08–5.23 124–201 3.21–5.20

15–19 113–197 2.93–5.10 119–200 3.08–5.18

High-density lipoprotein cholesterol (HDL)

Adult

20–24 30–63 0.78–1.63 33–79 0.85–2.04

25–29 31–63 0.80–1.63 37–83 0.96–2.15

30–34 28–63 0.72–1.63 36–77 0.93–1.99

35–39 29–62 0.75–1.60 34–82 0.88–2.12

40–44 27–67 0.70–1.73 34–88 0.88–2.28

45–49 30–64 0.78–1.66 34–87 0.88–2.25

50–54 28–63 0.72–1.63 37–92 0.96–2.38

55–59 28–71 0.72–1.84 37–91 0.96–2.35

60–64 30–74 0.78–1.91 38–92 0.98–2.38

65–69 30–75 0.78–1.94 35–96 0.91–2.48

> 70 31–75 0.80–1.94 33–92 0.85–2.38

Child

Cord blood 6–53 0.16–1.37 13–56 0.34–1.45

5–9 38–75 0.98–1.94 36–73 0.93–1.89

10–14 37–74 0.96–1.91 37–70 0.96–1.81

15–19 30–63 0.78–1.63 35–74 0.91–1.91

Contd...

Clinical Chemistry 483

Low-Density lipoprotein Cholesterol (LDL)

Adult

20–24 66–147 1.71–3.81 57–159 1.48–4.12

25–29 70–165 1.81–4.27 71–164 1.84–4.25

30–34 78–185 2.02–4.79 70–156 1.81–4.04

35–39 81–189 2.10–4.90 75–172 1.94–4.45

40–44 87–186 2.25–4.92 74–174 1.92–4.51

45–49 97–202 2.51–5.23 79–186 2.05–4.82

50–54 89–197 2.31–5.10 88–201 2.28–5.21

55–59 88–203 2.28–5.26 89–210 2.31–5.44

60–64 83–210 2.15–5.44 100–224 2.59–5.80

65–69 98–210 2.54–5.44 92–221 2.38–5.72

> 70 88–186 2.28–4.82 96–206 2.49–5.34

Child

Cord

blood 20–56 0.52–1.45 21–58 0.54–1.50

5–9 63–129 1.63–3.34 68–140 1.76–3.63

10–14 64–133 1.66–3.44 68–136 1.76–3.52

15–19 62–130 1.61–3.37 59–137 1.53–3.55

SI Units

Cholesterol

esters

60–75% of total or 0.60–0.75

< 210 mg/dL < 5.43 mmol/L

Free

cholesterol

< 50 mg/dL < 1.29 mmol/L

LDL:HDL

ratio

< 3 < 3

Clinical Relevance

1. Increased levels of cholesterol

 a. Levels above 250 mg/dL are considered elevated

and call for a triglyceride test.

 b. Conditions related to elevated cholesterol

 1. Cardiovascular disease and atherosclerosis

 2. Type II, familial hypercholesterolemia

 3. Obstructive jaundice (also an increase in

bilirubin)

 4. Hypothyroidism (decreased in hyperthyroidism)

 5. Nephrosis

 6. Xanthomatosis

 7. Uncontrolled diabetes

 8. Nephrotic syndrome

 9. Obesity.

 c. Free versus esterified cholesterol.

 There is a markedly abnormal ratio of free to esterified

cholesterol in disease of the liver biliary tract,

infectious disease, and extreme cholesterolemia.

2. Decreased levels of cholesterol

 a. Conditions where cholesterol is not absorbed

from the gastrointestinal tract

 1. Malabsorption

 2. Liver disease

 3. Hyperthyroidism

 4. Anemia

 5. Sepsis

 6. Stress

 7. Drug therapy such as antibiotics.

 b. Other disorders related to decreased cholesterol

levels

 1. Pernicious anemia

 2. Hemolytic jaundice

 3. Hyperthyroidism

 4. Severe infections

 5. Terminal stages of debilitating diseases such as

cancer

 6. Hypolipoproteinemias.

 c. Esterol fraction decreases in liver diseases,

liver cell injury, malabsorption syndrome, and

malnutrition.

3. Increased levels of cholesterol esters are associated

with familial deficiency of Lecithin—cholesterol

acyltransferase (LCAT).

4. Decreased levels of cholesterol are associated with

liver disease. This is because persons with liver

diseases may have impaired formation of LCAT with

a resulting deficiency of the enzyme.

5. Cholesterol ester storage disease causes accumulation

of cholesterol esters in the tissues, but it has no effect

on the percentage of esterified cholesterol in the

blood.

6. The higher the cholesterol phospholipid ratio, the

greater the possible risk of developing atherosclerosis.

Interfering Factors

1. Cholesterol is normally slightly elevated in pregnancy.

2. Estrogen decreases plasma cholesterol and oophorectomy increases it.

3. Many drugs may cause a change in the blood cholesterol

Patient Preparation

1. Advise patient about fasting for a night for 12 hours

before the test.

2. Water is permitted.

3. Before fasting, the patient should be on a normal diet

for 7 days before testing.

Contd...

484 Concise Book of Medical Laboratory Technology: Methods and Interpretations 4. No alcohol should be consumed 24 hours before

testing.

5. Lipid lowering drugs such as estrogen, oral contraceptives,

and salicylates should be withheld.

 

2. Contrast media 24 hours before measurement may

cause an altered reaction.

3. A high fat meal may cause decreased bilirubin levels

by interfering with the clinical reactions.

4. Air bubbles and shaking of the specimen may cause

decreased levels.

5. Foods (carrots, etc.) and drugs increase the yellowish

hue in the serum.

6. Refer to the Many drugs can interfere with Bilirubin

tests for a listing of the many drugs that may interfere

with testing for bilirubin.

7. Hemolyzed blood will falsely elevate bilirubin level.

Comments

1. In severe obstructive jaundice with formation of

biliverdin, low results for the degree of jaundice will

be obtained since biliverdin does not react with the

diazo reagent and cannot be determined.

2. An unusual source of otherwise unexplained elevated

serum bilirubin has been described following 48 hours

fasting. A normal bilirubin value from 0.68 mg% may

rise to the abnormal range at 1.87 mg%.

Icterus Index

The icterus index is a measure of the degree of icterus

(yellowish-green color) in a plasma or serum specimen

in cases of jaundice. This is just a screening test for

hyperbilirubinemia. Substances other than bilirubin

in the serum (carotene, xanthophyll, hemoglobin, etc.)

may contribute to the icterus index, therefore, limiting its

clinical utility. The test is now considered to be obsolete.

Reagents

A. Potassium dichromate solution

 1. Stock solution (1%)

 Dissolve 1 g of potassium dichromate in 70 mL of

water placed in a 100 mL volumetric flask. Add 2

drops of sulfuric acid and dilute to 100 mL mark

with distilled water. Store in a glass-stoppered

brown/amber colored bottle.

 2. Working standard solution (0.1%)

 Pipette 10 mL of the stock solution into a 100 mL

volumetric flask and dilute to 100 mL mark with

distilled water.

B. Saline (0.9% NaCL) isotonic.

Method

A. Dilute the serum specimen ten times with saline (1 mL of

serum mixed with 9 mL of saline) in a test tube and mix.

B. Transfer the diluted serum into a cuvette and read

absorbance at 420 to 460 nm. If too dark, dilute further

478 Concise Book of Medical Laboratory Technology: Methods and Interpretations and multiply the final reading with the dilution factor

utilized here.

C. Determine the icterus index from the calibration curve.

Multiply the result by dilution factor. If the serum is

diluted ten times, the dilution factor is 10.

Calibration Curve

A. Prepare three concentrations of the standard by diluting appropriate quantities of the stock solution of

potassium dichromate in three 100 mL volumetric

flasks

 1. Five mL stock mixed with 95 mL of water (1:20).

This corresponds to 5 units.

 2. 25 mL of stock solution made to 100 mL with water

(1:4 dilution). This corresponds to 25 units.

 3. 50 mL of stock solution made to 100 mL with water

(1:2 dilution). This corresponds to 50 units.

B. Read the absorbance of each working standard

solution corresponding to 5, 25 and 50 units at 420 to

460 nm using water as blank.

C. Tabulate the results with the units of icterus index and

the corresponding absorbance values.

D. Plot a calibration curve and use this for the determination of icterus index.

TOTAL PROTEINS

Biuret Method

(Courtesy: Tulip Group of Companies)

For the determination of total proteins in serum and

plasma (for in vitro diagnostic use only).

Summary

Proteins are constituents of muscle, enzymes, hormones

and several other key functional and structural entities

in the body. They are involved in the maintenance of the

normal distribution of water between blood and the tissues.

Consisting mainly of albumin and globulin the fractions

vary independently and widely in diseases. Increased

levels are found mainly in dehydration. Decreased levels

are found mainly in malnutrition, impaired synthesis,

protein losses as in hemorrhage or excessive protein

catabolism.

Principle

Proteins, in an alkaline medium, bind with the cupric ions

present in the biuret reagent to form a blue-violet colored

complex. The intensity of the color formed is directly

proportional to the amount of proteins present in the

sample.

Proteins + Cu++→ Blue violet colored complex

Normal Reference Values

Serum and plasma : 6.0–8.0 g/dL

It is recommended that each laboratory establish its

own normal range representing its patient population.

Contents 150 mL 2 × 150 mL

Carton 1

L1: Biuret reagent 150 mL 2 × 150 mL

Carton 2

S: Protein standard ( 8 g/dL) 5 mL 5 mL

Storage/Stability

Carton 1 : Biuret reagent is stable at RT till the expiry

mentioned on the label.

Carton 2 : Protein standard is stable at 2–8°C till the

expiry mentioned on the label.

Reagent Preparation

Reagents are ready to use. Protect from bright light.

Sample Material

Serum or plasma. Proteins are reported to be stable in the

sample for 6 days at 2–8°C.

Procedure

Wavelength/filter : 550 nm (Hg 546 nm)/yellow-green

Temperature : RT/37°C

Light path : 1 cm

Pipette into clean dry test tubes labeled as blank (B),

standard (S), and test (T)

Addition

Sequence

B

(mL)

S

(mL)

T

(mL)

Biuret reagent (L1) 1.0 1.0 1.0

Distilled water 0.02

Protein standard (S) - 0.02

Sample - - 0.02

Mix well and incubate at 37°C for 10 minutes or at RT

for 30 minutes. Measure the absorbance of the standard

(Abs S), and test sample (Abs T) against the blank, within

60 minutes.

Calculations

 Abs T

Total proteins in g/dL = _________ = × 8 Abs S

Linearity

This procedure is linear upto 15 g/dL. If values exceed

this limit, dilute the sample with distilled water and

Clinical Chemistry 479

repeat the assay. Calculate the value using the proper

dilution factor.

Note

Do not use if the reagent shows turbidity or black

precipitates.

System Parameters

Reaction : End point Interval :

Wavelength : 550 nm Sample vol : 0.02 mL

Zero setting : Reagent blank Reagent vol : 1.00 mL

Incubation

temperature

: 37°C/RT Standard : 8 g/dL

Incubated

time

: 10 mm/30 min Factor :

Delay time : React slope : Increasing

Read time : Linearity : 15 g/dL

No. of read : Units : g/dL

SERUM ALBUMIN

Determination of Serum Albumin (BCG Method)

(Courtesy: Tulip Group of Companies)

For the determination of albumin in serum or plasma (for

in vitro diagnostic use only).

Summary

Albumin consists of approximately 60% of the total

proteins in the body, the other major part being globulin.

It is synthesized in the liver and maintains the osmotic

pressure in blood. Albumin also helps in the transportation

of drugs, hormones and enzymes. Elevated levels are

rarely seen and are usually associated with dehydration.

Decreased levels are seen in liver diseases (hepatitis,

cirrhosis). Malnutrition, kidney disorders, increased fluid

loss during extensive burns and decreased absorption in

gastrointestinal diseases.

Principle

Albumin binds with the dye bromocresol green in a

buffered medium to form a green colored complex. The

intensity of the color formed is directly proportional to the

amount of albumin present in the sample.

Albumin + Bromocresol green→ Green albumin BCG

complex.

Normal Reference Values (Albumin)

Serum, plasma (albumin) : 3.7–5.3 g/dL

Globulin : 2.3–3.6 g/dL

A/G Ratio : 1.0–2.3

It is recommended that each laboratory establish its

own normal range representing its patient population.

Contents 150 mL 2 × 150 mL

Carton 1

L1: BCG reagent 150 mL 2 × 150 mL

Carton 2

S: Albumin standard (4 g/dL) 5 mL 5 mL

Storage/Stability

Carton 1 : BCG reagent is stable at RT till the expiry

mentioned on the label.

Carton 2 : Albumin Standard is stable at 2–8°C till the

expiry mentioned on the label.

Reagent Preparation

Reagents are ready to use. Protect from bright light.

Sample Material

Serum, EDTA plasma. Albumin is reported to be stable in

the sample for 6 days at 2–8°C.

Procedure

Wavelength/filter : 630 nm (Hg 623 nm)/Red

Temperature : RT

Light path : 1 cm

Pipette into clean dry test tubes labeled as blank (B),

standard (S), and test (T):

Addition

Sequence

B

(mL)

S

(mL)

T

(mL)

BCG reagent (L1) 1.0 1.0 1.0

Distilled water 0.01 - -

Albumin Standard (S) - 0.01 -

Sample - - 0.01

Mix well and incubate at RT for 5 minutes. Measure

absorbance of the standard (Abs S), and test sample (Abs T)

against the blank.

Calculations

 Abs T

Albumin in g/dL = ________ × 4 Abs S

Globulin in g/dL = (Total proteins) — (Albumin)

 (in g/dL) (in g/dL)

 Albumin in g/dL A/G Ratio = _________________

 Globulin in g/dL

Linearity

The procedure is linear upto 7 g/dL. If values exceed this

limit, dilute the sample with distilled water and repeat

480 Concise Book of Medical Laboratory Technology: Methods and Interpretations the assay. Calculate the value using the proper dilution

factor.

Note

Gross hemolysis, ampicillin and heparin interfere with

the results. Elevated bilirubin and lipemic samples may

have a slight effect on accuracy. For grossly lipemic

samples run a sample blank by adding 0.02 mL sample

in 2 mL distilled water. Read the absorbance against

DW and substract the blank absorbance from the test

absorbance.

System Parameters

Reaction : End point Interval :

Wavelength : 630 nm Sample

volume

: 0.01 mL

Zero setting :  Reagent

blank

Reagent

volume

: 1.00 mL

Incubation

temperature

: RT Standard : 4 g/dL

Incubated time : 5 minutes Factor :

Delay time : — React slope : Increasing

Read time : — Linearity : 7 g/dL

No. of read : —- Units : g/dL

Normal Values

Total Proteins

SI units

Adults 6.0–8.0 g/dL 60–80 g/L

Children

Premature 4.3–7.6 g/dL 43–76 g/L

Newborn 4.6–7.4 g/dL 46–74 g/L

Infant 6.0–6.7 g/dL 60–67 g/L

Child 6.2–8.0 g/dL 62–80 g/L

Specimen Collection and storage

1. Serum is the specimen of choice.

2. Avoid excessive hemolysis since every 100 mg/dL

of hemoglobin corresponds to about 100 mg/dL of

albumin.

3. Albumin in serum is reported stable for one week at

room temperature (18–30°C) and approximately one

month when stored in the refrigerator (2–8°C) and

protected against evaporation.

Clinical Relevance

Causes of Hypoalbuminemia

Reduced synthesis

¾ Malnutrition

¾ Malabsorption syndromes

¾ Chronic inflammatory diseases

¾ Acute hepatitis (lasting 14 days or more)

¾ Chronic liver disease

¾ Genetic abnormalities.

Increased Loss

¾ Nephrotic syndrome

¾ Massive burns

¾ Protein-losing enteropathy.

Increased catabolism

¾ Massive burns

¾ Widespread malignancy.

Multifactorial

¾ Cirrhosis

¾ Congestive heart failure

¾ Pregnancy.

Increased albumin levels are generally not observed

(When albumin concentration decreases there is a relative

increase in globulins. However, there is a definite rise in

globulins in mono/polyclonal gammopathies).

Disorders Associated with Polyclonal

Gammopathies

Chronic liver disease

¾ Nutritional cirrhosis

¾ Primary biliary cirrhosis

¾ Chronic active hepatitis

¾ Viral hepatitis.

Collagen diseases

¾ Rheumatoid arthritis

¾ Systemic lupus erythematosus

¾ Sjögren’s syndrome

¾ Felty’s syndrome

¾ Polymyositis

¾ Scleroderma.

Chronic Infections

¾ Tuberculosis

¾ Osteomyelitis

¾ Deep fungi

¾ Syphilis

¾ Bronchitis.

Miscellaneous

¾ Metastatic carcinoma

¾ Cystic fibrosis

¾ Recovery from trauma.

 

Urea standard/serum/diluted urine 0.01 mL

Incubate at the assay temperature for 1 minute and add

Starter reagent (L2) 0.2 mL

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

standard and test.

Sample Start Assay

Pipette into a clean dry test tube labelled Standard (S) or

Test (T):

Addition (S)/(T)

Sequence 37°C / 30°C / 25°C

Working reagent 1.0 mL

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

standard and test.

For Standard ∆AS = A2S – A1S

For Test ∆AT = A2T – A1T

Calculations

 ∆A T

Urea in mg/dL = __________ × 40 ∆A S

Linearity

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

dilution factor.

Note

Plasma should not be collected with fluoride or heparin

salts as contamination by ammonia or ammonium salts

lead to erroneous results.

System Parameters

Reaction : Fixed time kin. Interval : 60 sec.

Wavelength : 340 nm Sample

volume

: 0.01 mL

Zero

setting

:  Distilled

Water

Reagent

volume

: 1.00 mL

Incubation

temperature

: 30°C/37°C Standard : 40 mg/dL

Incubated time — Factor :

Delay time : 30 seconds React slope : Decreasing

Read time : 60 seconds Linearity : 250 mg/dL

No. of read : 2 Units : 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.

Clinical Relevance

Common Causes of Increased BUN or Uremia

Prerenal

¾ Reduced blood flow to kidney

¾ Shock, blood loss, dehydration

¾ Increased protein catabolism

¾ Crush injuries, burns, fever, hemorrhage into soft tissue

or body cavities, hemolysis.

Renal

¾ Acute renal failure

¾ Glomerulonephritis, malignant hypertension, nephrotoxic drugs or metals, renal cortical necrosis

¾ Chronic renal disease

¾ Glomerulonephritis, pyelonephritis, diabetes mellitus,

arteriosclerosis, renal tubular disease, collagen-vascular

diseases.

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

a. Liver failure.

b. Negative nitrogen balance as may occur in malnutrition, excessive use of IV fluids and physiologic

hydremia of pregnancy.

c. Impaired absorption as in celiac disease.

d. Occasionally in nephrotic syndrome.

e. Overhydration.

Interfering Factors

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

men.

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

• Dextrose infusions

• Phenothiazines

• Thymol.

Comments

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

55–56oC.

4. Plasma or serum preserved with fluoride cannot be

used as this inactivates the enzyme. Urea is stable in

frozen serum for months.

5. Make sure that there is no contamination by ammonia

or heavy metal ions.

6. For a small laboratory, commercially available multi/

monostep kits can be used.

Plasma or Serum Creatinine

Normal Values

Conventional units SI units

Jaffe, manual method 0.8–1.5 mg/dL 70–133 µmol/day

Jaffe, kinetic or enzymatic method

Adult

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

Children

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).

Summary

Creatinine is the catabolic product of creatinine

phosphate which is used by the skeletal muscle. The daily

production depends on muscular mass and it is excreted

out of the body entirely by the kidneys.