A nitrite test is a chemical test used to determine the presence of
nitrite
The nitrite ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite also ...
ion in solution.
Chemical methods
Using iron(II) sulfate
A simple nitrite test can be performed by adding 4 M
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
to the sample until acidic, and then adding 0.1 M
iron(II) sulfate
Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the heptahydrate (''x'' = 7) but several values for x are know ...
to the solution. A positive test for nitrite is indicated by a dark brown solution, arising from the iron-nitric oxide complex ion. This test is related to the
brown ring test for the nitrate ion, which forms the same complex in a ring. In contrast, nitrites turn the whole solution brown and therefore interfere with that test.
Griess test
A common method of quantitative nitrite detection is the Griess test, which relies on the reaction of nitrite with the two components of a Griess reagent to form a red
azo dye
Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C-N ...
. This allows the concentration of nitrite to be determined by
UV-vis spectroscopy.
:
Urinary nitrite test
A nitrite test is a standard component of a
urinary test strip. A
positive test for nitrites in the urine is called nitrituria.
This test is commonly used in diagnosing
urinary tract infection
A urinary tract infection (UTI) is an infection that affects part of the urinary tract. When it affects the lower urinary tract it is known as a bladder infection (cystitis) and when it affects the upper urinary tract it is known as a kidne ...
s (UTIs). A positive nitrite test indicates that the cause of the UTI is a
gram negative
The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram.
Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
organism, most commonly ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
''. The reason for nitrites' existence in the presence of a UTI is due to a bacterial conversion of endogenous nitrates to nitrites. This may be a sign of infection. However, other parameters, such as
leukocyte esterase Leukocyte esterase (LE) is an esterase (a type of enzyme) produced by leukocytes (white blood cells). A leukocyte esterase test (LE test) is a urinalysis, urine test for the presence of white blood cells and other abnormalities associated with infec ...
, urine white blood cell count, and symptoms such as
dysuria
Dysuria refers to painful or uncomfortable urination.
It is one of a constellation of ''irritative'' bladder symptoms (also sometimes referred to as lower urinary tract symptoms), which includes nocturia and urinary frequency.
Diagnosis
The c ...
,
urinary urgency
Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...
, fevers, and chills must be correlated to diagnose an infection.
False negative
A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resul ...
nitrite tests in urinary tract infections occur in cases with a low
colony forming unit
In microbiology, colony-forming unit (CFU, cfu or Cfu) is a unit which estimates the number of microbial cells (bacteria, fungi, viruses etc.) in a sample that are viable, able to multiply via binary fission under the controlled conditions. Count ...
count, or in recently voided or dilute urine.
[Urinary Tract Infection: Providing the Best Care]
By Margaret A. Fitzgerald. Medical Writer: Sandra M. Nettina. Published: 06/24/2002; Updated: 06/24/2003. In addition, a nitrite test does not detect organisms unable to reduce nitrate to nitrite, such as
enterococci,
staphylococci
''Staphylococcus'' is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillales. Under the microscope, they appear spherical ( cocci), and form in grape-like clusters. ''Staphylococcus'' species are facultati ...
(''
Staphylococcus saprophyticus
''Staphylococcus saprophyticus'' is a Gram-positive coccus belonging to the genus '' Staphylococcus''. ''S. saprophyticus'' is a common cause of community-acquired urinary tract infections.
History
''Staphylococcus saprophyticus'' was not reco ...
''),
Acinetobacter
''Acinetobacter'' is a genus of gram-negative bacteria belonging to the wider class of Gammaproteobacteria. ''Acinetobacter'' species are oxidase-negative, exhibit twitching motility, and occur in pairs under magnification.
They are importan ...
, or
adenovirus
Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from ...
.
[
]
See also
*Nitrate test
A Nitrate Test is a chemical test used to determine the presence of nitrate ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in ...
*Saliva testing
Saliva testing or Salivaomics is a diagnostic technique that involves laboratory analysis of saliva to identify markers of endocrine, immunologic, inflammatory, infectious, and other types of conditions. Saliva is a useful biological fluid fo ...
; salivary nitrite levels can serve as a surrogate biomarker for nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ...
, a natural cardioprotective factor, derived from nitrate-rich leafy green vegetables which are often found in anti-hypertensive diets, such as the DASH diet
The DASH diet (Dietary Approaches to Stop Hypertension) is a dietary pattern promoted by the U.S.-based National Heart, Lung, and Blood Institute (part of the National Institutes of Health (NIH), an agency of the United States Department of Heal ...
[ Friday, 5 April 2019 ]
References
Chemical tests
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