Urine changes When Urine Left at Room Temperature and Without Preservatives
Precautions in the collection of urine:
- Proper collection and the handling of the urine are important to get accurate results. It depends upon:
- Containers used should be clean, dry, and proper for the sample.
- Should follow proper collection procedure.
- Storage conditions are also important.
- A proper preservative is also important to get accurate results.
- Disposable inert plastic containers with a secure cap are the best for urine collection.
- When urine is left in the lab at room temperature for a longer period (maybe over 24 hours), biochemical and microbiological changes occur.
- For routine urine analysis, freshly voided urine is a better sample than the catheterized sample.
- Avoid the contamination of urine from the vaginal secretion (discharge) or hemorrhage.
- Get the clean voided midstream urine, particularly for the bacteriological examination.
- It may be needed to pack the vagina or use the tampoon to avoid vaginal contamination.
- The best sample to check urine glucose is one voided 2 to 3 hours after the last meal.
- This is the exception of the early first-morning sample.
- The key importance is to check the fresh or suitably preserved urine, usually refrigerated.
- Examine urine within 30 minutes of the collection, as the changes (decomposition) start during this time.
- Try to examine the urine in the first 1 to 2 hours of collection.
- Urine is the best culture media for the growth of bacteria.
- If it is delayed, then refrigerate the urine at 4 °C.
- Urine left at room temperature >2 hours is not acceptable.
- Urine preservatives are only accepted for 24 hours of urine collection and not for a routine examination.
Urine sample to be rejected:
- When urine has incorrect preservatives.
- When the urine quantity is insufficient.
- When urine is not collected with all needed precautions.
- When there is a missing or incomplete request form.
- When urine has no proper identification.
- When urine shows contamination like stool, etc.
Some articles favor that urine should be examined within two hours of collection.
Urine changes when collected and left in the lab:
- Urine normally becomes hazy or cloudy, when let at room temperature. This can be reversed by adding few drops of acid.
- Vaginal contamination is quite a common cause of cloudy urine in a female patient.
- The normal color of the urine darkens on standing for longer than 30 minutes, due to oxidation of urobilinogen to urobilin.
- Red blood cells: These are distorted because of the lack of isotonic solution.
- RBCs become crenated or swell, which makes them difficult to recognize.
- Finally, RBCs disintegrate.
- White blood cells: WBCs disintegrate in a hypotonic solution.
- Cast: These will disintegrate, especially as the urine becomes alkaline, but these casts need acidic urine and solute for their existence in the urine.
- The alkalinity of urine: Other substance which appears in the acidic urine will disappear in the alkaline urine.
- Alkalinity develops because of the growth of the bacteria and the production of ammonia.
- Bacteria: These will multiply and obscure the various components.
Changes when urine left for a longer period of time at room temperature:
|Urine Substance||Changes taking place||How change takes place (a mechanism)|
|pH||It will increase and is alkaline||This is due to the breakdown of urea to ammonia|
|Color||Urine will become darker||Due to oxidation or reduction of metabolites|
|Turbidity||This will increase||Due to bacterial growth and crystal precipitation|
|Odor||This will be foul-smelling/increased||Due to bacterial decomposition of urea and ammonia|
|Cast||Decreased or disappeared||These are dissolved|
|Glucose||It is decreased||This is due to glycolysis.|
|Bilirubin||It is decreased, and the color changes yellow to green.||Bilirubin oxidized to biliverdin.|
|Urobilinogen||It is decreased, and color changes colorless to orange-red.||Urobilinogen oxidized to urobilin.|
|Acetone (Ketones)||This is decreased||This is due to the evaporation of acetone.|
|Acetoacetic acid||This is decreased||This is converted into acetone and evaporation.|
|Nitrite||This will increase||Due to bacterial production|
|Cells||These may disappear or decrease.||This is due to lysis.|
|Red blood cells||These are lysed||Due to alkaline urine|
|WBC||These will disintegrates||Due to dilute alkaline urine|
|Bacteria||Their number will increase.||Due to bacterial proliferation|
Urine changes without preservatives:
|Characteristics||Reason for the changes
|Change in color||Darkened due to:
|Change in turbidity||This is due to:
|Change in odor||Increased due to:
|pH||Increased due to:
|Low pH (false)||This is due to:
|High pH (false)||This is due to:
|Glucose||Decreased due to:
|False-negative glucose||This is due to:
|False-positive glucose||This is due to:
|Ketones||Decreased due to:
|False-negative ketones||This is due to:
|Nitrite||Increased due to:
|False-positive nitrite||This is due to:
|False-negative nitrite||This is due to:
|Bilirubin||Decreased due to:
|False-negative bilirubin||This is due to:
|Urobilinogen||Decreased due to:
|False-negative urobilinogen||This is due to:
|Destruction of cells or cast||This is due to:
|Increased number of bacteria||This is due to:
|Red blood cells||Decreased due to:
|White blood cells||Decreased due to:
|Casts||Decreased due to: