UREA unilag mbbs/bds 300, 2nd semester

urine is a solution of water and waste products of metabolism in including man. It is a very complex fluid whose examination and produce useful information about the milieu interior. Since urine is readily available. only very little time is spent in obtaining valuable
information necessary for diagnosis and management of several disease.

Plasma is filltered by the glomerular membranes of the kidneys.The glomerular filtrate has a similar composition to other filtrates through membranes of the body. e.g. the cerebrospinal fluid and the interstitial fliud.

The glomerular filtrate passes through the kidneys which produce urine and store it in the bladder until voided.

Collection of the urine
Urine specimens must be properly collected in order to obtain reliable information from the results of its analysis.

First morning specimen:
Empty the bladder before retiring at night, discard, then collect the
morning specimen on rising.

Random: A single collection of urine anytime, day or night, in a clean container detergent-free. The container must also be sterile for
bacteriological examination ).. The best and most concentrated specimen of urine is obtained first thing in the morning

Fasting :Empty the bladder, more than four hours after ingestion of food or water; discard and then collect the next specimen”

24 hour specimen:

Empty the bladder and discard.
Collect for the next 24 hours, including the specimen passed. exactly, after 24hours. Specimens passed during defaecation must be
included.. Keep the specimen in a refrigerator during collection.
Add 5 ml of 10 percent thymol in propanol to preserve the urine

Midstream specimen of urine:(M.S.U)
Pass the first stream of urine to clean the passage. Collect the next stream in a clean and sterile container and pass out the rest .Replace the cover immediately and tightly.

. Empty the bladder immediately before a meal.
. Collect the next specimen of urine.

Colour : Normal urine is clear, straw-coloured or light brown due to the presence of “urochrome” – normal metabolites of bile and other pigments. A very concentrated urine such as ma-v be passed in starvation has a dark brown colour

Dark yellow : Bilirubin , Haemoglobin from haemolysis e.g. as in G6PD deficiency Porhyrins

Smoky: Red blood cells

Bloody: Haematuria, the red cells settle on standing.

Turbid/milky: Alkaline urine containing phosphate precipitate
. Acid urine containing urates
. Bacteria in infections
. Epithelial cells
.Stale urine which has become alkaline due to the production of ammonia from urea by bacteria: phosphates are therefore precipitated
other colours usually drugs e.g. blue in methylene brue colouring in diet or of sweets.

Volume: A healthy adult on normal diet excretes about 1.5L of urine in 24 hours. The volume is less in children.
. In anuria. there is no secretion of urine
. In oliguria. the l-l hour secretion is less than 1L
. In polyuria the 24hour volume is in excess of 1.5 to 2L.
Polyuria and oliguria may be due to phychological or pathological causes while anuria is certain due to renal disease.

Smell: Fresh normal urine has no smell.
Stale urine has ammoniacal smell due to the action of bacteria on urea.

Ketone bodies: Acetone smell in starvation or in diabetes mellitus.

Hdrogen ion concentration:(PH)
Normal urine ranges from pH 5 to 8.5 With an average of 6.0 for an
individual on mixed diets. The limits are maintained by the kidneys.

Acid urine is passed in acidosis and alkaline urine in alkalosis. On standing, carbon dioxide escapes from the urine and the pH increases; the action of bacteria on urea also increases the pH of stale urine. A vegetarian diet also produces an alkaline urine.
Only fresh urine must be tested.

For measurement of pH use:
Dip-stix e.g. multistix or universal indicator paper.
Graded pH paper or Closed glass electrodes.

The use of double indicator paper e.g. methyl red and bromocresol blue measures
a colour range from orange through yellow and green to blue. The indicators are impreenated into “stix” and cover the entire urinary pH range.

Measurement with glass electrodes is a potentiometric analysis. A difference in
electrical potential is measured betrveen two solutions of different pH separated b.

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