Urinalysis
Types of Samples
There are several different types of urine sample that can be collected. These are used for different purposes. Firstly we will consider those used for diagnosing a urinary tract infection.
Mid-Stream Urine Collection (MSU)
This is the most commonly used sample and can be used for both adults and older children. By using the mid-stream of the urine contamination from skin bacteria is minimised.
Patient instructions for doing a MSU
Female:
- Spread the labia apart.
- Pass small amount of urine into toilet.
- Continue to urinate and collect in sterilised container.
- Close container immediately and label.
Male:
- Retract the foreskin.
- Pass small amount of urine into toilet.
- Continue to urinate and collect in sterilised container.
- Close container immediately and label.
Collection bottles for MSU
You can use a normal white topped bottle for collection. Red topped sample bottles are often used. These contain a preservative which helps keeps bacteria alive whilst the sample is waiting to be processed.
Sample analysis
The urine sample is sent to the microbiology laboratory for "m,c & s" ( microscopy, culture and sensitivity) i.e. Can any white / red blood cells be seen in the sample, are there any bacteria in the sample and if so which antibiotic can be used for treatment?
Catheter specimen of urine (CSU)
Patients with indwelling catheters are more prone to urinary tract infections as they have a foreign body within the bladder. A sample of urine can be taken from these patients via the sampling port on the catheter.
Clean catch urine
Urinary tract infections are not uncommon among infants and young children; however this group of patients are unable to produce a sample on demand. Ideally the nappy should be removed and when the child urinates a sample should be caught in a sterile container.
Other samples from infants
Clearly the clean catch method can be difficult to achieve. In this instance a bag with an adhesive seal can be placed over the infants’ perineum and the urine collected in it. Although this is an easier method of collection contamination from the skin bacteria is much more likely. If a sample is needed urgently a needle can be inserted directly into the bladder to obtain a suprapubic aspirate.
Transportation and analysis of the samples
All the samples mentioned above can be used for detecting the presence of urinary tract infections.
Collection bottles
The containers for transporting the sample need to be sterile. There are two main types of containers which are used. A white topped bottle can be used for collection of any sample. It is also used for transportation of the sample within a hospital setting. In general practice the sample may have to wait for up to 24 hours to be transported to the laboratory for analysis. Therefore there are red topped bottles available that contain bolic acid which helps to preserve any bacteria until the sample reaches its destination. Any sample taken should be labelled immediately as described previously.
Sample analysis
The urine sample is sent to the microbiology laboratory for microscopy, culture and sensitivity (m,c & s). There it will be examined under the microscope to look for any red or white blood cells or any bacteria in the sample. A gram stain may be performed. The sample will then be cultured in an attempt to grow and bacteria which might be present. If the culture is positive sensitivity testing can be done to establish which antibiotics can be used to treat the infection.
Other types of samples
Finally we should consider other types of sample which can be used for different purposes.
24 hour urine collection
In this case the patient is asked to collect all the urine passed in a 24 hour period. The patient is instructed to empty their bladder at 9am on the day of collection and then to collect all the urine passed until 9am the following day. Obviously a container large enough for this purpose is provided. This technique is useful for quantitative analysis for the exact amount of substances in the urine, e.g. measurement of protein for diagnosing nephritic syndrome.
Early morning urine sample
This is the most concentrated sample of the day. Traditionally this has been used for pregnancy testing, although most tests are now sensitive enough to detect the pregnancy hormone in low concentrations.