Urinalysis

• What is urinalysis?
• How is urinalysis performed?
• When is urinalysis used?
• Preparing for urinalysis
• What happens during urinalysis?
• What do the results mean?
• Benefits and limitations of urinalysis

What is urinalysis?

Urinalysis is a term used to describe a process used to examine urine using chemical and/or physical means. Urinalysis consists of whole host of chemical and microscopic tests, and it is a useful screening tool for diseases such as urinary tract infections, renal disease, and other diseases of the body which result in the formation of compounds that can be detected in the urine at abnormal levels. The urinalysis has proven itself as a procedure that can be performed relatively quickly and easily while providing the doctor with lots of useful information.

How is urinalysis performed?

There are two different categories of analysis of urine, each of which looks at different substances in the urine:

Gross and chemical exam

• Urine appearance and colour – e.g. can be described as clear, cloudy, turbid, layered, pale yellow, dark yellow, red, green, & blue
• Bilirubin (breakdown product of red blood cells)
• Urobilinogen (breakdown product of bilirubin)
• Glucose
• Haemoglobin
• Ketones
• Nitrite
• Urine pH; usually 4.6 – 8.0 with an average of 6.0
• Urine protein
• Specific gravity (the weight of the urine compared to that of the same quantity of water); normal is between 1.006 and 1.030

Microscopic exam

• Bacteria and other microorganisms
• Casts
• Crystals
• Fat
• Mucous
• Red Blood Cells

Dipstick urinalysis is a method of chemical examination of the urine and involves the use of a plastic strip which contains a series of pads that change colour according to specific chemical reactions. Results are read off this strip by comparing it to a chart shows levels of substances in the urine depending on the colour change that occurred. The dipstick, as the name suggests, is dipped into the urine and then the person performing the test must wait for the colour change to occur before attempting to interpret the results.
Urine microscopy is performed by a trained doctor using a light microscope, and requires a well trained eye.

When is urinalysis used?

The urinalysis is used as a tool to assess patients for early signs of disease, not only concerning the genitourinary tract but also diseases of other organs. A dipstick examination of the urine is the standard screening test for haematuria (blood in the urine).

Preparing for urinalysis

To make sure the test gives you the most accurate results it is important that the patient informs the doctor about the drugs that they are taking, since some of these can affect results.
A “clean catch” mid stream urine (MSU) should be taken. The “clean catch” means that the sample should be taken without contamination from the external genitals, and the mid stream urine means that only the middle part of the urine stream is collected. Therefore it is important to clean the external genitalia in both males and females before urinating to prevent contamination.
It is also important that the urine sample is analysed within 30-60 mins of collection, so patients should preferably provide a urine sample when they are with their doctor.
The urine is most concentrated the first thing in the morning and it is therefore preferred urine be collected at this time.
 

What happens during urinalysis?

The procedure involves no pain or discomfort, only normal urination, however some may find it awkward when collecting the sample.
To correctly collect a mid stream urine sample you should follow these steps:

• Begin to urinate allowing a small amount to fall into the bowl.
• After passing a small amount of urine in the bowl, pass urine into the container provided removing it when it is almost full.
• Give the container with the lid in place to your health care provider or the assistant.

Following the procedure you may be able to view your results immediately if all that was required was a dipstick test.

What do the results mean?

Interpreting the results is done by the health care provider, reading a colour chart and comparing it to the colours on the dipstick. A trained doctor needs to perfom the microscopic analysis of the urine.
Many abnormalities can be found, but the doctor will take into account your history and examination findings and then make one or more appropriate diagnoses.
Further tests may be needed if the doctor suspects that there is something wrong.

Benefits and limitations of urinalysis

Benefits

• Dipsticks are simple, fast and easy to use
• Dipsticks can be performed by anyone who isn’t colour blind
• There is little pain or discomfort involved in collecting the patients urine during urinalysis
• There are no risks or precautions associated with urinalysis
• The test is easily reproducible and can be performed daily as a baseline measurement
• It has the ability to diagnose a wide variety of conditions

Limitations

• Many of the dipstick results aren’t completely accurate, and sometimes gives you false positive results.
• The test relies on correct collection of sample by the patient, and if this is not done properly the results may be inaccurate
• Many of the abnormalities seen with urinalysis can be found in normal people

References

1. Burton DR & Post TW. ‘Uptodate – Urinalysis’ [online], Uptodate, 2006, Available at URL: http://www.uptodate.com (last accessed 01/03/2006)
2. Datta V. ‘Medline Plus – Urinalysis’ [online], Medline Plus, 2006, Available at URL: http://www.nlm.nih.gov/medlineplus/ency/article/003579.htm (last accessed 02/03/2006)
3. ‘Harrisons Chapter 260 – Acute Renal Failure’ [online], McGraw Hill’s AccessMedicine, Available at URL http://www.accessmedicine.com (last accessed 02/03/2006)
4. Talley NJ & O’Connor S. Clinical examination. 4th ed (1st Indian edition) New Delhi. JP Brothers 2003