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.
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 or etc.
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: