Microbiology Laboratory

URINE CHEMISTRY using combi strip

Written by MicroDok

AIM: To detect rapidly the abnormal levels of unorganized deposits/abnormal chemical constituents (ascorbic acid, bilirubin, blood, glucose, ketone, nitrite, pH value, protein, specific gravity, urobilinogen) in urine specimens as an aid in the diagnosis of urinary tract infections (UTI’s).

MATERIAL/APPARATUS: uncentrifuged urine specimen, combi – 9 – test strip, test tubes, test tube rack, discard jar.


  1. Describe the appearance of the urine specimen based on its colour and turbidity.
  2. Dispense the urine specimen into a clean test tube.
  3. Immerse the combi – 9 – test strip into the urine specimen and remove immediately, making sure that all the test area of the strip are covered.
  4. Hold the combi – 9 – test strip in a horizontal position upon removal from the urine specimen, in order to prevent interaction from adjacent test areas of the strip.
  5. Compare the reagent areas on the strip with that of a standard provided by the manufacturer of the test strip in order to read the result appropriately. This is normally done by holding the test           strip close to the colour chart on the container label of the test strip container. Ensure not to      contaminate the container with the urine on the strip while carrying out this procedure.


Any deviation/change in colour of the test areas on the Strip when compared to the standard (which indicates normalcy) as provided by the manufacturer is indicative of an abnormality and should be reported as “positive” using the + sign depending on the extent of the change in colouration.

NOTE: The result of this test should not be read beyond 10 seconds, as a false positive result might be reported due to a drying effect.


Urine is produced and excreted by the kidneys. A normal human being excretes about 1 – 2 liters of urine every 24 hours (per day), though the volume of urine excreted by the kidney depends on our daily fluid intake, diet, climate (hotness & coldness of the environment), and other physiological factors of the body. The functional unit of the human kidney is called nephron and each of the kidneys contains over a million nephrons that controls and filters fluid that passes through the kidney.

pH: The normal reaction of freshly passed urine is slightly acidic, around pH 6.0. A normal urine contains about 95% of water, including electrolytes (magnesium, potassium, sodium, chloride, bicarbonate), and waste products of metabolism (urea, uric acid, and creatinine). The pH of the body is very important because it helps in maintaining a proper acid – base balance in the body.

Protein: An abnormal level of protein in urine is called proteinuria, and this condition can be caused by renal diseases such as pyelonephritis & glomerulonephritis, UTI’s, nephritic syndrome, and urinary schistosomiasis. Proteinuria should always be considered to indicate underlying disease until proved otherwise.

Glucose: Glucose can be found in the urine of diabetic patients, and occasionally in some healthy persons. Presence of more than the usual amount of glucose in urine is called glycosuria/glucosuria, and it is caused by a rise in the level of the blood glucose, and a reduced rate of reabsorption of glucose by the kidney tubules. Whenever glucose is found in urine, the blood glucose level should be measured in order to clear all doubts about diabetes.

Ketones: Ketonuria is a condition in which there are abnormal levels of ketone/ketone bodies in urine. Ketones are found in the urine of persons suffering from starvation, dehydration following prolonged vomiting and diarrhea, or untreated diabetes. Ketones are toxic to the brain and their accumulation can result to coma experienced by diabetic ketoacidosis patients.

Bilirubin: Bilirubin is found in the urine of persons with hepatocellular jaundice or cholestatic (obstructive) jaundice. It is not normally detected or found in the urine and when detected, the condition is called bilirubinuria.

Urobilinogen: Urine specimen is detected for the presence of urobilinogen when diagnosis points to abnormal haemolysis or liver disorders in which liver function is impaired. Nevertheless, it is normal to detect small amounts of urobilinogen in the urine.

Blood (Haemoglobin): The presence of free haemoglobin in urine is called haemoglobinuria. It occurs in bacterial infections like Escherichia coli septicaemia and typhoid fever, acute glomerulonephritis, UTI’s, severe falciparum malaria e.t.c.

Nitrite: The presence of nitrite in urine shows the presence of a bacterial infection as the urine of a healthy person does not contain nitrite. Detection of nitrate in urine is indicative of UTI’s which is normally caused by nitrate reducing bacteria. These pathogenic bacteria have the ability to reduce nitrate found in urine to nitrite

Specific Gravity: The relative mass density (formally known as specific gravity) of urine gives information regarding the concentrating and diluting ability of the kidneys. The normal relative mass density of urine varies from 1.002 – 1.025 depending on the state of hydration of the person and the time of the day. The ability of the kidneys to concentrate and dilute urine is reduced in renal failure of the kidneys.

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