A nitrite test is a chemical test used to determine the presence of nitrite

Nitrite

The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...

 ion in solution.

Chemical method

A common nitrite test can be performed by adding 4 M sulfuric acid to the sample until acidic, and then adding 0.1 M iron(II) sulfate

Iron(II) sulfate

Iron sulfate or ferrous sulfate is the chemical compound with the formula FeSO4. Known since ancient times as copperas and as green vitriol, the blue-green heptahydrate is the most common form of this material...

 to the solution. A positive test for nitrite is indicated by a dark brown solution, arising from the iron-nitric oxide complex ion.

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

Urinary tract infection

A urinary tract infection is a bacterial infection that affects any part of the urinary tract. Symptoms include frequent feeling and/or need to urinate, pain during urination, and cloudy urine. The main causal agent is Escherichia coli...

s. A positive nitrite test indicates that the cause of the UTI is a gram negative organism, most commonly Escherichia coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

. 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, the other parameters such as leukocyte esterase, urine white blood cell count, and symptoms such as dysuria

Dysuria

In medicine, specifically urology, dysuria refers to painful urination.Difficult urination is also sometimes described as dysuria.It is one of a constellation of irritative bladder symptoms, which includes urinary frequency and haematuria....

, urinary urgency

Urinary urgency

Urinary urgency is a sudden, compelling urge to urinate. It is often, though not necessarily, associated with urinary incontinence, polyuria, nocturia, and interstitial cystitis. It tends to increase with age...

, fevers and chills must be correlated to diagnose an infection.

False negative nitrite tests i urinary tract infections occur in cases of with a low colony forming unit count, or in recently voided or dilute urine. In addition, a nitrite test does not detect organisms unable to reduce nitrate to nitrite, such as enterococci, staphylococci, or adenovirus.

See also

• Nitrate test
  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 water. In contrast, many common ions give insoluble...
  
  : similar, but uses concentrated sulfuric acid
  Sulfuric acid
  Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
  
   to test for nitrate
  Nitrate
  The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
  
  ion.