Dipstick Assay for Urinalysis

7/27/2019 Dipstick Assay for Urinalysis

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Chemical Test Principles

Dipstick Assay for Urinalysis


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Bayer Multistix Product Insert
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Dipstick

Dipstick or reagent strips

Strip of plastic containing small pads of reagents

Each pad contains a colorimetric reagent to

detect a different analyte Color generated is proportional to concentration

of the analyte present in the sample.


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Dipstick Assay Analytes

1. Glucose

2. Bilirubin

3. Ketones4. Specific Gravity

5. Blood

6. pH

7. Protein

8. Urobilinogen9. Nitrite

10. Leukocytes

Available in commercial urine

dipsticks


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Test Principle - Glucose

Reagents on the dipstick:

EnzymesGlucose Oxidase, Peroxidase

ChromogensPotassium Iodide,

Tetramethylbenzene, o-tolidene, 4-

Aminoantipyrene

Note:

1) This test will work only for glucose. Other sugars such assucrose, lactose, galactose and fructose cannot be detected.

2) Other reducing sugars can be detected using the Benedicts test.

However, this involves a heating step. The sensitivity of the

Glucose Oxidase method is more than that of a Copper reduction

test such as Benedicts test.


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Test Principle - Bilirubin

Reagents on strip:

2,4-dichloroanilene diazonium salt,

2,4-dichlorobenzene diazonium salt

Note:

1) This test may give false negatives upon

prolonged exposure of the urine sample to light.

Bilirubin is photosensitive, and gets converted

into Biliverdin upon light exposure.


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Test Principle - Ketones

Reagents on strip: Sodium Nitroprusside

Note:1) This test will not detect Acetone or

hydroxybutyric acid.


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Test Principle - Blood

Reagents on the strip:

Diisopropylbenze dihydroperoxide,

3,3,5,5-tetramethylbenzidine

Note:

1) This test can usually show free Hb, myoglobin as well asRBCs. Upon testing, RBCs will lyse, and form a speckled

pattern on the pad.

2) False positives may arise from the presence of oxidizing

contaminants in the sample.


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Test Principle Specific Gravity

X+ + Polymethyl vinyl ether / maleic anhydride

---------------> X+-Polymethyl vinyl ether / maleic anhydride + H+

H+ interacts with a Bromothymol Blue indicator to

form a colored complex

Reagents on stripPoly(methyl vinyl ether/

maleic anhydride) , Sodium Hydroxide,

Bromothymol Blue

1.000

1.005

1.010

1.015

1.020

1.025

1.030Note:

1) These readings will not be accurate in case

the urine is alkaline.

2) Test does not measure non-ionized solutes

such as glucose.


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Test Principle - pH

H+ ions react with Methyl Red and

Bromomethyl Blue indicators to form

coloured complexes.

Methyl Redhigh conc. of H+ , low pH

Bromothymol Bluelow conc. of H+ ,

high pH

Reagents on strip : Bromothymol Blue,

Methyl Red

Note:1) These reagents can indicate pHs between 5.0 and 8.5.

2) Values of pH may be affected by certain medications, or

bacterial growth in the sample.

3) In a commerical dipstick, buffers from the next reagent

zone for protein may also run-over into the pH zone andprovide an incorrect value.


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Test Principle - Protein

Based on the Protein Errors of Indicators

method. The point of colour change of some

indicators is different in the presence of a protein

than in the absence of the protein. This is due to

proton accepting behavior of proteins at a

constant pH

Reagents on strip:

Tetrabromphenol, acidic buffer.

Note:

1) Test is sensitive to albumin, but not to globulins,

Bence-Jones proteins, and muco-proteins.

2) Highly alkaline urine will lead to false positives.


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Test Principle - Urobilinogen

Ehrlich Aldehyde Reaction

Reagents on strip:

Paradiethylaminobenzaldehyde

Note:

1) Several interfering substances such as p-

aminosalicylic acid, sulfonamides, p-aminobenzoic

acid may react with the reagent.

2) Test cannot indicate the absence of Urobilinogen.


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Test Principle - Nitrite

Reagents on strip : Para-arsanilic acid,

1,2,3,4-tetrahydrobenzo (h)-quinolin-3-ol

Note:1) Bacterial overgrowth in sample with

interfere with the test.

2) Can only detect bacteria than reduce nitrate

to nitrite.


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Test Principle Leukocytes

Reagents on strip: Derivatised

pyrrole amino acid ester/ indoxyl

ester derivative, diazonium salt

Note:

1) False positives may occur in case strong oxidizing

contaminants are present

2) False negative may occur if the specific gravity is

high due to glucose or protein.


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List of Reagents from a Product

Insert

UrinCheck Healthscreen 10, Express Diagnostics, USA


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References

Graffs Textbook of Routine Urinalysis & BodyFluid, Chapter 4

Urinalysis - Francisco G. La Rosa, University of

Colorado

UrinCheck HealthScreen 10 product insert.

Practical Guide to Urine Analysis, Clinitek ProductInsert

Dipstick Assay for Urinalysis

Documents

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