Urinalysis can provide valuable information as regards the health of the patient and can test for indications of renal, urological and liver disease, diabetes mellitus and urinary tract infections (UTI) along with the hydration of the patient.
Urinalysis can be used to test for the presence of substances such as glucose, leucocytes, nitrites and blood none of which are found in a normal urine sample.
When to Test
Urinalsis is routinely carried out in doctors surgeries, outpatient clinics pre and post-operatively as well as in the emergency department (ED) where it can identify if the trauma patient has damgaed their kidneys. It is also useful in identifying when a patient may potentially have a UTI or kidney stones.
The Sample
The sample to be tested should be a mid stream urine (MSU), i.e. not containing urine from the initial flow as this may lead to false results due to debris from the urethra contaminating the sample. When the sample comes from a catheter it is referred to as a catheter stream urine or CSU. When samples are sent to the laboratory it is important that the form displays whether the sample is a CSU or an MSU as this will have a bearing on the results.
Initial Observations
- Colour - This varies depending on the concentration of the urine and can be straw coloured through to amber. A dark colour can indicate dehydration. Haematuria (blood in urine) can produce a bright red colour or even brown-green or a strong yellow colour but it is worth bearing in mind that some foods and drugs can change the colour of the urine, for example beetroot turns the urine red and the antibacterial drug rifampicin turns it an orange-red.
- Clarity - Cloudiness or debris can indicate the presence of pus, protein or white cells.
- Odour - urine does smell but when it is fresh the smell should not be offensive, however a fishy smell can indicate a UTI and a pear drop smell may suggest ketones are present. Again food stuffs can alter the smell, for example asparagus.
Testing the Urine and the Relevance of what is Tested
This is done using reagent strips which are very quick and simple to use. They can also be used in a multitude of settings from the hospital environment to the doctors surgery th the patients home.
- Specific gravity - (SG) this is the measurement of the total solute concentration in a fluid. The normal range is 1:001 - 1:035 (Marieb, 2001) A high SG suggests a concentrated urine and may indicate dehydration. A low SG in indicative of a diluted urine occuring in those with a high fluid intake, diabetes insipidus or hyperglycaemia.
- pH - urine is normally acidic with 5.0 - 8.0 being the normal range of pH. A low pH (acidic) may indicate urinary stone formation and alkalinity may indicate a UTI caused by certain types of bacteria such as proteus merabilis, klebsiella or pseudomanas (Higgins, 2007). the pH can also be influenced by dietary intake as a diet rich in protein can cause acidic urine and a diet rich in vegetables or dairy products can lead to alkaline urine.
- Protein - albumin protein molecules are generally too large to pass through the glomerular filtrate barrier in the kidneys therefore the presence of protein may indicate an increased permeability of the barrier as a result of infection or renal damage.
- Blood - haematuria is abnormal and be associated with problems in the urinary tract such as cancer, renal damage or stones. It may also be indicative of a blood clotting problem or a side effect of anti-coagulant drugs. Menstrual blood can also contaminate the urine.
- Glucose - glucosuria may be indicative of dibates mellitus however this is not diagnostic and a fasting blood sugar would be needed in order to confirm this. It can also occur in pregnancy and cases of physiological stress and in those taking corticosteroids.
- Ketones - these are an acidic chemical caused by the breakdown of fat, which can occur due to excesive vomiting, fasting, starvation and diabetes mellitus. Some drugs, for example captpril can cause false positive results (Roche, 2007).
- Urobilinogen and bilirubin - small amounts of urobilinogen can be normal however elevated levels may indicate liver damage or the abnormal breakdown of red blood cells. Bilirubin may indicate liver disease or biliary obstruction.
- Leucocytes - the presence of these indicate a UTI.
- Nitrites - these are the result of the breakdown of nitrates which are normally excreted in the urine, however gram negative bacteria such as e.coli contain the enzyme nitrate reductase which converts the nitrate into nitrite therefore the presence of nitrite in the sample suggests a UTI. Gram positive bacteria however do not have this enzyme and therefore a sample containing such bacteria will show negative, for example staphlococcus. When a UTI is still suspected due to the clinical picture of the patient it is important that the urine sample is sent to the laboratory for microscopy, culture and sensitivity in order to identify the offending bacterium.
The urine reagent strip is a valuable tool in diagnosis and is carried out routinely in many settings. The speed at which results are available affords prompt treatment because before the development of the strips results would take two to three days to become available. Prompt results provided by the reagent strips not only reassure patients and quicken treatment and recovery but they also cut down on manpower thus reducing cost and labour.
References
Blows W.T. (2002) The biological basis of nursing : clinical observations. Routledge, London.
Higgins C. (2007) Understanding laboratory investigations: for nurses and health professionals. 2nd edition. Blackwell Publishing, Oxford.
Marieb EN (2001) The urinary system in Marieb EN (ed) Human anatomy and physiology. 5th edition. Benjamin Cummings, san Francisco CA, 1003-1039.
Roche (2007) Diavant: Individual test areas. WWW.diavant.com
Staggall MJ (2007) Urine samples and urinalysis. Nursing standard. 22, 14-16, 42-45.
