Collection of urine samples

The use of a disposable container with a lid is recommended for the collection of urine samples. When non-disposable containers are used, cleaning materials or other contaminants must be carefully removed as trace amounts might produce erroneous results in chemical tests.

When urine is collected from small children or from persons who do not control their bladder sphincter, special sterile containers are used (i.e. adhesive collecting bags).

In order to obtain reliable results the following conditions must be satisfied :

  • The specimen must be fresh: minimizing the time between miction and testing reduces bacterial proliferation, avoids pH and glucose alteration and prevents cytolysis.
  • It must be concentrated: cellular elements are less diluted and hence better detected by microscopic examination.
  • It must be acidic: when the pH is acidic, albumin is less soluble and the morphological elements are better conserved.

The first morning urine normally satisfies all these conditions. This urine accumulates in the bladder during the night and is collected before breakfast or any other activity. Nocturnal accumulation produces very concentrated urine that is necessary for nitrite (bacteriuria) and protein detection. Fluctuations in protein concentration due to physical activity, posture or diet are decreased. This first morning urine is the most appropriate specimen for urinary test strips and microscopic analysis.

The second morning urine is obtained spontaneously after the first morning urine but before noon. It is appropriate for protein, enzyme and metabolite analysis when expressed relative to creatinine concentration. For the best sensitivity in the detection of glucosuria use urine obtained two hours after a meal rich in carbohydrates.

So called spontaneous urine is produced at any time or without any other restriction. It is the least complicated and most frequently used method in ambulatory medicine. Be aware that important chemical variations may be missed when dilute urine is analyzed. Such errors can worsen during the course of the day. It is dangerous to compare results of spontaneous urine samples because the tests were not conducted under similar dilution conditions. For correct interpretation of results, the specific gravity value must always be noted.

A routine urinalysis with urinary test strips and microscopic examination does not normally require a special cleaning of the genitals. However, precautions must be taken in females to prevent contamination of the urine with vaginal or menstrual discharge. A midstream samples is the appropriate specimen for a urine culture: urine is collected after the first brief miction is discarded and before miction is completed. Here is a description of the midstream urine collection procedure:

  1. Genitals must be thoroughly cleaned with lukewarm water, possibly with soap. Do not use disinfectants! The nursing personnel wear gloves.
    Men: the foreskin must be completely retracted to allow cleaning of the glans.
    Women: the vaginal labia must be spread to expose the urethral meatus. Clean in a forward to backwards direction. Rinse thoroughly and pad lightly until dry.
  2. The disposable container must be open just before collection of the sample. Any contact with the container’s interior walls must be avoided.
  3. The first stream is discarded in the toilet or in the bedpan. Midstream urine is then collected, avoiding any contact of the urine with the genitals. Discard the first and last stream.
  4. Close the container and immediately send the specimen to the laboratory.

Urine and indwelling catheter

In patients with indwelling catheters, urine must never be collected from the collection bag. Urine must be collected directly from the catheter after disinfecting its opening.

Hematuria is frequently detected in bedridden patients with indwelling catheters. It may be due to a catheter-induced lesion of the bladder wall or to some other cause.

24 hour urine

Renal excretion of metabolites, hormones, enzymes and drugs can be measured in 24 hour urine specimens.
The first morning urine is discarded at the beginning of the collection period. The next day’s first morning urine completes the 24 hour specimen collection period. During the collection period, urine should be kept at a low temperature and protected from light. Some decomposition is unavoidable during such a long period of time. In some instances, a preservative agent is added. The composition of this preservative agent varies according to the type of test requested. The amount of urine collected must be measured and registered precisely. At the end of the collection period, urine is mixed thoroughly. Two 10-20 ml samples will be sent to the laboratory with the total registered volume.

24h urine specimens are inappropriate for test strip or microscopic analysis (sediment).

Three-glass test in case of micro hematuria

Testing a first, second and last urine portion can distinguish between initial, terminal or total hematuria.

The three-glass test in case of prostatitis suspicion

Procedure:

  • First stream portion (first container)
  • Midstream portion (second container)
  • Urine after prostate massage (third container)

When a significant increase of leukocytes is observed in the third container, urine should be sent to the laboratory in a special tube for microbiological culture.
Prostate secretions can also be collected by massage. In this case, the sample should also be sent for microbiological culture.