URINE TEST AND COLLECTION
Consultant Pediatrician – B.J.Wadia Hospital for Children
Editor - Pediatric Oncall
Why is urine test required?
Urine is created by the kidneys. Kidneys remove water and various other waste products from the blood and form urine to discard the various wastes of the body. Thus kidneys purify the blood in this manner. Urine test thus helps to identify problems in the kidney functions, infections in the urine tract and various other problems in the blood stream.
What are the various aspects checked in a urine examination?
Urine examination involves checking the following:
pH = To look for acidifying function of the kidney. [Kidneys excrete hydrogen and bicarbonate ions in the urine to maintain pH of the blood]
Specific gravity = To look for concentrating and diluting power of the kidneys. [Kidneys tend to excrete more water if there is more water in the body thus causing dilute urine. If kidneys do not function in this manner, than water will accumulate in the body. Also if urine contains more salts then kidneys will excrete more water to prevent crystallization of these minerals to prevent stones. In case of dehydration, kidneys conserve water and thus urine excreted will be concentrated. In case of a condition called diabetes insipidus, kidneys are not able to concentrate urine.
Cells = Normally very few pus cells, red cells and epithelial cells are present in urine. Presence of many pus cells may suggest infection in the urine, presence of red cells may be seen with stones or kidney inflammation (glomerulonephritis) and epithelial cells may suggest a chronic kidney problem.
Casts = These are outer coatings of cells in the urinary tract. There may be several types of casts seen in various diseases such as waxy casts may be seen with nephrotic syndrome, pus cell casts may be seen with infection.
Albumin = Albumin is a protein present in the blood stream. Normally very little albumin is excreted in the urine. Presence of albumin in urine may suggest nephritic syndrome.
Sugar = Normally no sugar is present in urine. Presence of sugar may be seen with diabetes mellitus, renal tubular acidosis (RTA) and a liver disease called galactosemia.
Ketones = Normally no ketones are present in urine. Presence of ketones may occur with diabetes mellitus, starvation or other causes that cause low blood sugar.
Special tests = Sometimes special tests may be done on a urine sample such as urine electrolytes to look for conditions such as salt wasting and renal tubular acidosis (RTA) .
Urine culture = When an infection in the urine is suspected, urine is tested for bacteria. Urine is cultured and growth of bacteria is checked for. If more than 105 colonies of bacteria grow it suggests infection.
Urine crystals = In case of stones, urine may be checked for crystals. Also urine calcium, oxalate and uric acid content may be checked for to look for the type of stone.
Bile salts & bile pigments = Bile salts and bile pigments are checked in a patient with jaundice and presence of bile salts and bile pigments suggest a liver disease.
Colour of urine = Normally urine is white or pale yellow in colour. Various other colors may be seen in various conditions such as:
- Dark yellow colour: With jaundice, ingestion of multivitamins
- Brown colour: In oxaluria
- Red colour: Bright red colour may be seen with bleed or stones. Coca-cola colour may be seen with glomerulonephritis
- Pink colour: May be seen with phenolphthalein ingestion or with hemoglobin in urine.
- Orange colour: Seen with ingestion of rifampicin (a drug used for treating tuberculosis).
How is a urine collection done?
Before collecting urine, the genital area should be properly cleaned with soap and water. Mid stream urine is preferred as initial urine may be contaminated by bacteria from the genital area which may lead to erroneous results. Urine is collected in a clean container. Ideally the initial stream of urine is not collected and urine is directly collected in a wide jar container during mid stream. The jar is screwed tight with the lid and sent to the laboratory immediately for testing. In case of delay, the urine should be refrigerated. Delay in testing or improper storage may cause bacteria to multiply which will alter the pH and results of test.
Urine culture is collected in a sterile container obtained from the lab. Collection is similar described above. If urine culture tube cannot be sent to the laboratory immediately, it should be stored at -4o C and transported to the laboratory in ice.
Sometimes 24 hours urine may have to be collected to test for certain elements such as albumin, calcium, uric acid, oxalate, phosphorus and even genetic tests. Here urine is collected in a wide jar container over a period of 24 hours. Thymol crystals are placed in the urine to prevent decomposition of urine.
Sometimes in small babies or very ill patients, urine may be collected by inserting a catheter or by putting a needle straight into the bladder and aspirating urine through a syringe.
What are urine dipsticks?
There are commercially available dipsticks (multisticks) that test for presence of albumin (protein), sugar, blood and bacteria in urine. These strips are handy and give results in a few minutes. They are very useful for frequent monitoring of urine at home which may be required in patients with diabetes mellitus and nephrotic syndrome. Multisticks can test all the parameters whereas there may be separate glucosticks that will only measure glucose and separate protein sticks that will only check for proteins. Here dipsticks are dipped into the urine collected in a container for an interval specified by the manufacture and change in colour helps to identify the pathology.
Last updated on 24th December 2009