urine analysis

Last week while we were practicing some lab procedures in the college lab as a regular lab day, a student was practicing the procedure of urine analysis, while she is doing that she jumped with this question.

Q; What would happen to the urine sample that is left standing on the bench at room temperature for more than one hour? Is sugar in urine will turn to ketone? Or will the protein become creatinine? Or alkaline urine will become acid urine reaction? Or, maybe the bilirubin will no longer react? Or maybe the specific gravity will become lower? Which one is the correct answer?

I know the student who asked the question she is a smart student; she tried to figure the correct answer from me as this question was one of the review exam questions.

I don’t mind; I would be so happy to answer any question to any student.

When we work in the clinical laboratory, the integrity of the sample is very critical. Any change in the sample property will lead to the wrong result, either false positive or false negative, wrong lab result will mislead the provider to reach the correct diagnosis.

If the urine sample left at room temperature for longer the required time, then some biochemical and microbiological changes would happen.

Like;

RBCs will reduce in the sample and become crenated cells. Difficult to recognize them in the urine sample.

WBCs will crumble or crash because of the hypotonic solution. Difficult to recognize them in the urine sample.

PH will turn from acid PH to alkaline PH due to the production of ammonia by the growth of bacteria.

Cast will disintegrate, and they will dissolve.

Bacteria will grow in the sample, lead to confusing the other sample components.

Color will become darker because of  oxidation or reduction of metabolites

Turbidity will increase duo bacterial growth.

Glucose will decrease due to glycolysis

Bilirubin will decrease as will be oxidized to biliverdin.

Ketones will decrease due to the evaporation of acetone.

Nitrite  will increase due to bacterial production.

Now, let back to the question.

Some times you have to use your knowledge in addition to your skills of analytic, creative, and practical intelligence. The knowledge you gain from studying the subject of urine analysis, but in this question, you need to look out of the box. Why? If you back to the tone of the question, you will find there are two specific conditions, temperature and time. How would these two conditions help you to find the correct answer? Look at the answers which one related to the temperature and time? All of them but one is need another condition to consider it, which is ( maybe the bilirubin will no longer react). Bilirubin needs exposure to light for a certain period to oxidized to biliverdin. Which is correct, but leave it now, try to analyze the other answers or choices.

The other choices are;

Is the sugar will turn to ketone?

Or will the protein become creatinine?

Or alkaline urine will become acid urine reaction?

Or, maybe the specific gravity will become lower?

First one; is the sugar will turn to ketone? Can sugar turn to ketone? The answer is no. There is no way. The sugar in the urine sample will reduce due to glycolysis.  Ketone will reduce (if there is)because of the evaporation. So this answer is wrong.

The second one is, will protein become creatinine? When the body breaks, the protein will have amino acid and urea, not creatinine. It is wrong, as well.

The third one is, alkaline urine will become acid urine reaction? The change in the urine PH should be from acid to alkaline, not from alkaline to acid. Also, it is the wrong answer.

The fourth one is, the specific gravity will become lower? The specific gravity will increase, not decrease.

All of them are the wrong answer. Only one answer would make sense, which is the bilirubin will no longer react because there is no bilirubin any more. Still, we isolate this answer away because the question doesn’t mention anything about light.

This is what I meant by thinking out of the box.

Good luck.

you have a question, would be more than happy to help you to analyze the correct answer.