Case study - Chemical analysis of Urine

Question 1

When performing routi ne urinalysis qual ity control you observe when you remove the d ipsticks from the bottle that the
u robili nogen pad is of brown color. What is your course of action

Answer 1

Reagent pads should not be discolored immediately upon removal from the container. Discoloration in
any of the pads indicates that the reagent strips are either outdated or have not been stored properly. The urobilinogen reagent pad is particularly sensitive to moisture and may have turned brown. All discolored
reagent strips should be discarded and not used for diagnostic testing.

Question 2

When performing routine urina lysis you observe a pink calor on the bilirubin pad. How should you p roceed?

Answer 2

A pink col or may indicate an interfering substance. An Ictotest should be performed to rule in or rule out the presence of bilirubin. The test is reported as either negative if no purple color is observed or positive if there is a purple color.

Question 3

When performing a routi ne urinalysis you observe a 1 + leu kocyte esterase. No cel ls a re seen upon microscopic examination. What can account for these resu lts?

Answer 3

Leukocytes may have lysed if the urine is hypotonic. False-positive leukocyte esterase results can occur because of the presence of strong oxidizing agents, contamination of the urine with vaginal discharge, and preservatives such as formalin. Nitrofurantoin
contributes a col or to urine that may cause
misinterpretation of this test. Drugs that contain imipenem, meropenem, and clavulanic acid may cause false-positive leukocyte esterase results

Question 4

A urine test on a 1 -month-old baby shows a positive copper reduction test with a negative oxidase test. H ow should these resu lts be reported and what is their sign ificance

Answer 4

The oxidase test is specific for glucose and should be reported as negative for glucose. The copper reduction
test (Clinitest) is positive when any reducing substance is present. Because this test is not specific, it should be reported as positive for reducing substance

Question 5

A physician questions the resu lts of a urinalysis which was reported to show a negative n itrite, yet contained 2+
bacteria. Suggest a course of action and expla nation why these findings a re consistent.

Answer 5

The test may be repeated if requested by the physician.
However, the laboratory can also serve to educate healthcare providers about the causes for false-positive
and false-negative results in laboratory testing. A negative nitrite test should never be interpreted as indicating the
absence of bacterial infection. For nitrite, false-negative results can occur in urine with a high specific gravity or
elevated level of ascorbic acid. In addition, infection may be present even if the nitrite test is negative because:

1. there may be pathogens present in the urine that do not form nitrite;
2. the urine may not have remained in the bladder long enough for the nitrate to be converted to nitrite;
3. there are cases in which the urine does not
   contain any nitrate, so bacteria may be present but the dipstick will be negative;
4. under certain circumstances, the bacterial
   enzymes may have reduced nitrate to nitrite and then converted nitrite to nitrogen, which will give a negative nitrite result

Question 6

A urine chemical screening test resu lts in all negative resu lts and i ncl udes a specific g ravity of 1 .000. What other test
can be performed to determine whether the fl uid is actually urine?

Answer 6

If a urine specimen produces all negative results along with a very low specific gravity, it may not be urine. Testing for urea will verify that the specimen is urine. In addition, a creatinine test can be helpful with this same determination. The reagent strip method is available for the creatinine test.

Question 7

The brand of urine reagent strips you use at your facility i ncludes a pad for ascorbic acid (ascorbate). The pad g ives a reading of 2+.

1. What are the possible effects on other laboratory tests?
2. What does this result suggest about the nutritional status of
   the patient?
3. What could this result suggest about renal disorders in the
   patient?

Answer 7

1. What are the possible effects on other laboratory tests?
   - A positive ascorbate test indicates large amount of vitamin C are present, which can interfere with urine chemical screening tests.
2. false-negative blood by some reagent strips
3. false-negative glucose by reagent strip methods
4. positive reducing substance
5. decreased sensitivity for bilirubin
6. false-negative leukocyte esterase
7. What does this result suggest about the nutritional status of the patient?
   - this patient has a high level of vitamin C intake
8. What could this result suggest about renal disorders in the patient?

• If ascorbic acid is a constant finding in this patient’s urine, they can develop oxalate kidney stones.