Urine Analysis

URINE ANALYSIS

Urine examination is a very important diagnostic tool, which is easy to perform and gives immense information. It is mainly performed for 2 purposes.

1) Diagnosis and management of renal or urinary tract disease.

2) For detection of metabolic or systemic diseases not directly related to kidney.

Collection of urine sample:

It varies with the type of investigation. The first important step is the use of a clean, dry container. Disposable containers are preferred by most laboratories, since they avoid the possibility of contamination from improperly washed glass urine bottles. Samples that are to be cultured must be collected in sterile containers.

A random sample is usually sufficient for the performance of most urinary screening tests; but, since the first specimen voided in the morning (first-morning) is more concentrated it is usually the specimen of choice.

Clean-catch or clean-voided midstream urine (MSU) specimen is usually the method of choice for obtaining noncontaminated specimens. It is easy to perform and it provides a sample that can be used for bacteriologic examination as well as for routine urinalysis. Other methods of sample collection include catheterisation, suprapubic aspiration and collection using pediatric urine collectors.

For most of the quantitative estimations, a 24hr urine sample (timed collection) is required. Collection should begin at 8am in the morning and continued till 8am on the next day. The tests are generally carried out on a small volume of urine (100-150ml), called aliquot taken from the entire sample. 

Preservatives for urine: Ideally the urine should be tested as fresh as possible, but sometimes there may be a delay in transporting the urine sample to the laboratory. To avoid decomposition, especially in warm temperatures preservatives are to be used.

The preservatives include:

1) Refrigeration at 40C

2) Thymol crystals kept in a container (0.1g/100ml)

3) Formalin (6-8 drops of 40% solution /100ml of urine).

 4) Toluene (1ml/50ml of urine)

 5) Chloroform

6) Dilute acids (sulphuric acid, hydrochloric acid, boric acid).

Urine is examined under three headings:

1. Physical examination

2. Chemical examination

3. Microscopic examination