Chemical Analysis of Urine

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Chemical urinalysis is performed to identify or evaluate the bilirubin, blood (whole blood and hemoglobin), glucose, ketones, leukocyte esterase, nitrate, pH level, protein, and urobilinogen in the urine. Chemical analysis of the urine provides health practitioners with information about the patient's kidney and liver function, carbohydrate metabolism, and acid-base balance.

Chemical tests use reagent strips, also called dipsticks, to identify the presence and concentration of the labeled substances. Reagent strip testing can be performed manually by dipping the strip into urine and comparing the color changes on the strip to the appropriate color chart. Reagent strips can also be inserted into an automated strip reader that analyzes the strip, displays the results, and creates a printed document. The findings of reagent testing are often confirmed by additional chemical tests called confirmatory tests. Chemical testing should be done within an hour of sample collection; if not, the urine should be stored in a refrigerator.

Bilirubin

A reagent strip is used to detect the presence of bilirubin in the urine. Bilirubin is formed in the liver, spleen, and bone marrow when hemoglobin is broken down. It is then transported to the liver and is normally excreted in the stool. Bilirubin in the urine is an indication of abnormal conditions of the liver or bile ducts. If the bilirubin reagent test indicates the presence of bilirubin, a confirmatory test called the Ictotest is performed. The Ictotest is a specific bilirubin test.

Normal Findings. Normal urine does not contain detectable bilirubin.

Variations from Normal. Bilirubin in the urine is seen in diseases such as hepatitis, obstructed biliary tract, or other liver disorders. The presence of bilirubin can also indicate liver damage caused by exposure to toxins or drugs.

Interfering Circumstances. Since direct light causes decomposition of the bilirubin, the urine specimen should be protected from exposure to light. Certain drugs, vitamin C, nitrites, and the age of the sample may alter the reliability of the test.

Blood

Urine is routinely evaluated for the presence of blood, red blood cells, and hemoglobin. Blood that is visible in the urine is a nonspecific symptom and necessitates additional analysis. The presence of red blood cells is called hematuria and the presence of hemoglobin is known as hemoglobinuria. The reagent strip is used to detect the presence of red blood cells and hemoglobin in the urine. A positive result may indicate the need for microscopic analysis of a fresh urine specimen.

Normal Findings. Negative for blood, red blood cells, and hemoglobin.

Variations from Normal. Blood in the urine is a nonspecific abnormal finding that may indicate infection or trauma of the urinary tract, or bleeding in the kidneys. Red blood cells in the urine can be an indication of bleeding somewhere along the urinary tract, which may be caused by urinary tract infection, trauma, neoplasms, or other urinary system abnormalities.

Hemoglobin is an indication of an abnormal condition outside of the urinary system. Conditions that demonstrate hemoglobin in the urine are burns or injuries, hemolytic anemias, severe infections, smallpox, malaria, mushroom poisoning, renal infarction, and reactions to blood transfusions.

Interfering Circumstances. Myoglobin, an oxygen-carrying substance similar in structure to hemoglobin but formed in muscles, reacts with the blood reagent strip. Various substances can cause a false-negative or false-positive result.

Glucose

The presence of glucose in urine is an abnormal condition known as gluco-suria or glycosuria. The reagent strip test and the Clinitest are used to detect glucose in urine. Both tests rely on color change to identify the presence of glucose. The most common cause of glycosuria is diabetes mellitus.

Normal Findings. Negative for glucose.

Variations from Normal. Positive glucose tests may indicate diabetes mellitus, or Cushing's syndrome, a pituitary gland disorder. Glucosuria may also signify the malfunction of glucose reabsorption by the kidneys.

Interfering Circumstances. Time of the testing, particularly after a heavy meal, and a vitamin C excess may cause a false-positive glucose test. In addition, stress, certain fruits and other foods, and drugs may cause a positive urine glucose test.

Ketone

Ketone urine testing is done to detect the presence of ketones, also called acetone or ketone bodies, in the urine. This condition, known as ketonuria, is a manifestation of abnormalities that limit the metabolism of carbohydrates. When carbohydrates cannot be metabolized, fats are metabolized to meet the body's energy needs and excessive amounts of ketones are produced and excreted into the urine. Ketonuria is detected by the reagent strip test and confirmed by the Acetest.

Normal Findings. Negative, that is, ketones are not detected.

Variations from Normal. Ketonuria is seen in a variety of conditions such as uncontrolled diabetes, anorexia, diets low in carbohydrates and high in fats, starvation, fasting, or excessive vomiting. Pregnancy and fever may cause ketonuria.

Interfering Circumstances. Certain drugs can produce false-positive ketone tests. Urine must be capped and refrigerated since ketones evaporate at room temperature.

Leukocyte Esterase

The purpose of the leukocyte esterase urine test is to identify the presence of granulocytic leukocytes, primarily neutrophils, in the urine. The primary granules found in neutrophils contain esterase, an enzyme that breaks down fats. Esterase reacts with the reagent strip when it is present in the urine. A positive reagent test is cause for a microscopic examination to confirm the presence of neutrophils or bacteria. The leukocyte esterase is not performed in all laboratories.

Normal Findings. Negative for leukocyte esterase and white blood cells.

Variations from Normal. The presence of white blood cells in the urine indicates urinary tract infection or inflammatory disorder.

Interfering Circumstances. Contamination of the urine specimen with vaginal bleeding, mucus, or other substances can produce unreliable results. Vitamin C, protein, and some drugs may yield a false-negative result.

Nitrites

The nitrite urine test is a screening test that may indicate a urinary tract infection (UTI). This test may not be included in the routine urinalysis in all laboratories. Nitrites are found in the urine when nitrate, a substance normally present in urine, is converted to nitrites by the action of enzymes produced by gram-negative bacteria. Nitrites produce a chemical reaction in the reagent strip. A positive reagent test result should be verified by microscopic examination, or urine culture and sensitivity tests. The best urine specimen for nitrite testing is the morning specimen that has been in the bladder overnight. The clean-catch method should be used to prevent contamination of the specimen. A negative nitrite urine test may not indicate the absence of a UTI since some bacteria do not convert nitrates to nitrites.

Normal Findings. Negative for the presence of nitrites.

Variations from Normal. A positive nitrite urine test may indicate the present of a UTI caused by microorganisms such as Escherichia coli, proteus, pseudomonas, or klebsiella.

Interfering Circumstances. Bacterial contamination of the urine specimen alters test results.

The pH of urine is measured to determine its acidity or alkalinity. A reagent strip color change indicates the pH value of the sample. Acidic urine has a pH below 7 and alkaline urine has a pH above 7. Urine pH is a useful screening tool for diagnosing metabolic disorders, renal disease, and respiratory disease.

Normal Range

Urinary pH 4.6-8.0 Average pH 6.0

Variations from Normal. Urine pH that exceeds the upper limit of the normal range may be indicative of UTIs, chronic renal failure, and respiratory disease with hyperventilation. Urine pH that does not meet the lower limit of the normal range can be associated with uncontrolled diabetes, emphysema, starvation, diarrhea, and certain respiratory diseases. The pH results are not disease specific and should be evaluated with other diagnostic studies.

Interfering Circumstances. Improper handling and storage of the urine specimen can affect pH levels. Diet and medications can alter pH results. Diets high in animal fat may result in acidic urine and those high in citrus may produce alkaline urine.

Protein

The urine of a normal person is usually free of protein, although a trace of protein in the urine specimen may not be unusual. The reagent strip is used to detect the presence or absence of protein, indicated by the color of the strip. Presence of increased amounts of protein in the urine is called proteinuria and is an indication of renal or systemic diseases.

The Bence-Jones protein test is performed to identify the presence of Bence-Jones protein in the urine. This specific protein is named for Henry Bence-Jones, an English physician. The protein is found almost exclusively in the urine of individuals who have multiple myeloma.

Since the reagent strip test does not identify the Bence-Jones protein, a precipitation test is necessary. Under appropriate test conditions, the Bence-Jones protein settles out of the urine sample. A positive Bence-Jones protein test is cause for additional tests to confirm the neoplastic diagnosis.

Normal Findings. Absence of all protein, including the Bence-Jones protein.

Variations from Normal. Positive urine protein tests can be attributed to diseases such as nephrosis, glomerulonephritis, pyelonephritis, and polycystic kidney disease. Urinary tract infection, diabetes, systemic lupus erythematosus (SLE), as well as poisoning from various chemicals and drugs, can result in proteinuria. The Bence-Jones protein is associated with neoplastic disorders such as multiple myeloma, lymphoma, and lymphocytic leukemia.

Interfering Circumstances. Certain medications, foods, exercise, emotional stress, pregnancy, and other circumstances can cause protein to be temporarily present in the urine. False-positive Bence-Jones protein findings can occur when the patient is receiving high doses of aspirin or penicillin. Connective tissue disease and chronic renal insufficiency also generate a false-positive Bence-Jones protein level.

Urobilinogen

The urobilinogen test is performed to determine the amount of urobilinogen in the urine. Urobilinogen is a compound created by the action of bacterial enzymes on bilirubin. Bilirubin enters the intestine in the bile and is converted to urobilinogen by bacterial enzymes. In a healthy individual, urobilinogen is excreted in feces. Urobilinogen that is not excreted is absorbed into the blood and returned to the liver where it is recycled via the bile.

A small amount of urobilinogen is normally present in most urine and is determined by the reagent strip. Urobilinogen levels can assist in the diagnosis of liver and bile duct diseases and disorders. The reagent strip test does not detect the absence of urobilinogen.

Normal Range

Urobilinogen 0.0-1.0 Ehrlich U/dl (Ehrlich units)

Variations from Normal. An increase in urobilinogen levels can be seen in cirrhosis of the liver, acute hepatitis, pernicious and hemolytic anemias, and hemorrhage. The absence of urobilinogen may indicate an obstructive disorder of the biliary duct system.

Interfering Circumstances. Urobilinogen decomposes when exposed to light or when stored at room temperature. Since urobilinogen is formed by intestinal bacteria, patients who are on antibiotic therapy may have lower urobilinogen levels. In addition, certain medications may increase or decrease urobilinogen and therefore negatively affect the reliability of this urine test.

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  • Dina
    What chemicals indicate bilirubine presence in urine?
    11 months ago

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