Urine analysis – part 7 – 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.
- A proper collection procedure should be followed.
- 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) then biochemical and microbiological changes take place.
- For routine urine analysis, freshly voided urine is a better sample than the catheterization is suitable.
- 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 to 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.
There are articles that favor that urine should be examined within two hours of collection.
Urine changes when collected and left in the lab:
- Red blood cells: These are distorted because of the lake 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 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: