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Urine testing

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Many Wells, MSc, RN, RM, Dip N (Lond), nurse consultant for Integrated Bladder and Bowel Care, Devon PCT.

What is it?

Urinalysis is an extremely valuable tool for diagnosis and screening. It is cheap and simple to perform and can indicate a variety of disorders and diseases (Wells, 1997).

How does it work?

Immersing the Reagent Test Strips into fresh urine allows chemical reaction to occur between the two elements and provides of means of diagnosing numerous potential ailments and illnesses.

A urine culture is indicated in the following circumstances: 

  • In the presence of diabetes or pregnancy;
  • When there is doubt about the diagnosis;
  • When there is a patient history of urinary infection within the past three weeks and where there may be a relapse from the previous urinary infections and/or an antibiotic resistance;
  • When there is a history of recent urinary tract instrumentation.

What is it used for?

Reagent Test Strips can be used to detect the following:

Glucose: Glycosuria is often indicative, but never diagnostic, of diabetes mellitus. Glycosuria in a person known to have diabetes can indicate poorly controlled diabetes.

Protein: Finding protein in hypertensive patients suggests renal disease. A similar principle applies in diabetes. Proteinuria can be detected before other symptoms of the condition arise.

Blood: The presence of blood (both macroscopic and microscopic haematuria) is a potentially serious sign (Lloyd, 1993), especially when there are no other symptoms, such as pain present. Haematuria is also found in the presence of a urinary tract infection and disappears with resolution of the infection. However urinalysis dipsticks are extremely sensitive to blood and may therefore give a false positive result (Jou and Powers, 1998).

Haematuria may be a sign of urological cancer. Serious disease is more likely if the blood is visible (microscopic) in smokers and patients over 50 years. Only a minority of people with microscopic haematuria will have significant pathology, although investigation should still be considered via the GP/hospital doctor and they should be informed if either type of haematuria is found.

If there is frank haematuria the patient should be referred to urologist via a urological cancer referral pathway when they will be investigated urgently.

Urobilinogen: It is normal to find urobilinogen in the urine. The level rises in the urine in the presence of some hepatic diseases (typically hepatitis) and with haemolysis. It is totally absent in biliary obstruction.

Bilirubin: Bilirubin is not normally found in the urine and is found typically in obstructive jaundice (Lloyd, 1993; Thompson, 1991).

Nitrites: Nitrite in the urine is produced by the action of bacterial nitrate reductase on dietary nitrate. The presence of nitrites is an important sign of a urinary tract infection, although staphylococci, enterococci and pseudomonas species do not produce nitrate reductase. Therefore its absence does not exclude infection. False positives or false negatives can occur depending on dietary intake.

Leucocytes: Leucocyte esterase is an enzyme found in leucocyte granules and can also be used in the diagnosis of a urinary tract infection. The dipstick test has been validated against counts of 105 colony forming unites (CFUs) per ml on a single species and leucocyte counts of 103 or more per ml of urine (Gray and Malone-Lee, 1996). The sensitivity of the test (proportion of true positives) is 7596%; the specific (proportion of true negatives) is 9498% (Pfaller and Koontz, 1985; Komaroff, 1986). But it must be understood that in a symptomatic patient the sticks may be insensitive since a significant colony count is 102 CFUs per ml. Antibiotic therapy can cause a false positive test (Beer et al, 1996).

Ketones: Ketones are produced from anaerobic metabolism. Their presence on the urine suggests dehydration, starvation or in combination with glucose in a person known to have diabetes, could indicate uncontrolled diabetes mellitus. The presence of ketones in a diabetic is potentially an extremely serious matter, and should prompt notification to a doctor.

pH: Normally the pH of urine varies from 4.5 to 8.0, and reflects the acid base balance of the body, values being lowest after an overnight fast and highest after meals. Urine pH is low in acidaemia and high in alkalaemia. A high urine pH can produce a false positive test for proteinuria.

Specific gravity: Normally urine specific gravity varies within the range of 1.0021.035.

How is it done?

Collect urine midstream or catheter specimens of urine (Mallet and Dougherty, 2004).

Before a urine specimen is obtained, it is important that the patient is given instructions on how to produce a specimen, why the sample is being collected and the reason for the test.

The following principles should be applied when performing urine testing:

  • Check the expiry date of the test strips on the bottle label;
  • Ensure storage instructions are adhered to the date of opening should be recorded on the bottle;
  • Precise timing is essential use a watch with a second hand;
  • Always test fresh urine, collected in a clean dry container if the urine is left standing for more than four hours, there may be contaminants, leading to false readings;
  • Immerse all the regent area in the specimen and remove the strip immediately;
  • Remove excess urine;
  • Hold the strip horizontally and compare the test areas closely with the colour chart on the bottle label for the length of time specified;
  • Record the results in nursing records and report any abnormal findings.

Some drugs can cause false negatives or false positives. Check package insert for test strips.

Normal values

Colour: The colour and clarity of the urine has significant implications and should always be noted (Torrance and Elley, 1998a; 1998b). The colour of normal urine varies with its concentration, from deep yellow to almost clear. In disease, the colour may be abnormal due to excretion of the endogenous pigments as well as drugs and their metabolites (Walker, 1990).

Odour: Odour in the urine of patients who have a urinary tract infection, is often due to the urea-splitting organisms. This makes it smell ammonia. The presence of urinary ketones, as in diabetic ketoacidosis, leads to an acetone smell. The presence of malodorous urine does not indicate the presence of infection and does not negate the need for testing.

Safety 

Do not leave samples standing out on work surfaces overnight, refrigerate in a specimen fridge. When possible, collect specimen in the morning, if in the community, get transport to the hospital the same day.

Nursing considerations

Urine should not be tested indiscriminately, but tested within the context of a patients illness or as a screening procedure (routine screening). Patients should have routine annual urine testing and results must be entered into the patients notes. Due to the prevalence of diabetes mellitus and renal dysfunction, routine urinalysis may be a useful screening tool.

Action to be taken if positive findings

It is important that any abnormal result from urinalysis is not taken in isolation. The patients clinical condition and medical history should be taken into account before any further action is taken. If the findings are new to the patients clinical condition and medical history warrant it, a medical doctor should be informed of the findings.

If a patient continues to complain of frequency and urgency after antibiotic therapy, a repeat urinalysis and/or MSU is appropriate to detect continuing infection.

Following appropriate assessment, the nurse should discuss with the medical staff the possibility that the patient may have detrusor overactivity and appropriate treatment commenced.

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