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Different Urine Tests, Different Preparation!

The instructions given to patients regarding urine testing is very important for accuracy of results. However, the inconvenience of delaying a test to obtain good preparation and a reliable report needs to be outweighed by the motivation and compliance of the patient. It is important to educate the patient about this and to give them the choice of timing of the investigation. However, if the patient is unlikely to complete the test at another time, it may be necessary to compromise the preparation and get the test done then and there.

Testing for genetic material by polymerase chain reaction is frequently done on urine samples (e.g. chlamydia and gonorrhoea). The result is most accurate when the urine is concentrated. Hence, the patient is advised to take a sample from the first or second urine passed in the morning. The urine sampled should be the first part of the urine stream, as this is most likely to contain infected mucus and debris, or, in the case of chlamydia and gonorrhoea, urethral cells that are infected with the intracellular organisms to be identified.

The significance of this has been demonstrated historically for decades by the visualisation of the first and second samples of the same urine stream passed. This was an old test for chlamydial and gonorrhoeal infection, as the urine cleared comparatively by midstream.

Collecting a urine sample for investigation of a urinary tract infection is quite different. For women and children in particular, the sample should ideally be done after a wash of the region to ensure less contamination from mucous and bacteria of genital and colonic origin. Wiping the area from front to back with damp tissues or toilet paper may be advised if a wash is impractical or not recently done. The midstream sample is best as it avoids the sometimes initially hesitant stream that may be contaminated by the genital bacteria before the urine sample is caught.  Men should be encouraged to expose the urethra if they are uncircumcised and so not pass urine through the foreskin first.

The identification of albuminuria or proteinuria is important in the assessment of kidney disease. The pre-test preparation is the same as for a urinary infection, but the result is more likely to be inaccurate (and falsely positive for proteinuria) if the patient has not washed first.  This test ideally should be done in the early morning (certainly not in the afternoon onwards) to avoid orthostatic proteinuria.

The necessity for accurate results from urine tests should not be underestimated. The incorrect pathology report may produce anxiety if indeterminate or positive, and may be falsely reassuring in the case of certain sexually transmitted diseases.