Chapter 14: Observations
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Source: Reproduced from Rigby and Gray ([178]) with permission of EMAP Publishing, Ltd.
Source: Adapted from Yates ([218]).
Evidence‐based approaches
Rationale
Urinalysis (urine testing) is commonly undertaken in clinical practice as a non‐invasive means of:
- measuring response to certain treatments
- assessing particular symptoms
- assisting in the diagnosis of medical conditions
- undertaking routine health assessments (Marini and Dries [112]).
Interpretation of urinalysis is generally based on reviewing all of the test's components and correlating them with the results of a physical examination and the patient's clinical signs and symptoms (Bickley [18]).
Carrying out a urinalysis can identify the level of ketones (and many other substances, such as proteins) in the urine; it can also identify bacteriuria (the presence of bacteria in the urine) (Bardsley [12]). However, urine specimens are rarely sterile, as a result of contamination with periurethral flora during collection (Weston [211]). Therefore, significant bacteriuria is defined as the presence of more than 105 organisms per millilitre of urine and the presence of clinical symptoms (Sheerin [187]). See Figure 14.41 for an illustration of significant bacteriuria.
Figure 14.41 Significant bacteriuria. Specimens of urine are rarely sterile. A cut‐off point is identified to distinguish true infection (significant bacteriuria) from the effects of contamination from surrounding tissues.
A clean‐catch urine sample should ideally be obtained to try to avoid contamination; however, if this is not practical, for example in infants, other methods should be used (NICE [141]). These include use of a pad, a catheter specimen of urine or a suprapubic aspirate collected via the rubber specimen side port (Herreros et al. [80], NICE [141]). An initial urine investigation with a dipstick, from a fresh spontaneous urine sample, is sufficient in most clinical situations; however, in other circumstances, a clean‐catch midstream urinalysis (MSU) will be required due to the risk of contamination in ‘spontaneous’ urine collected without any special hygiene precautions (Dolan and Cornish [54]). This is especially the case in women, where urine contains leucocytes in the presence of vaginal discharge and erythrocytes in the presence of the products of menstruation (Provan [167]). In addition, dipstick testing is not effective in catheterized patients as the presence of a catheter causes elevated pyuria without the presence of infection (NICE [130]).
When collecting an MSU, it is necessary to clean the genitals to ensure the culture specimen is processed with as little contamination as possible and to minimize the presence of contaminating elements, such as bacteria, analytes and formed particles (Adam et al. [2], Weston [211]).
Consideration must be given to whether a urine sample should be obtained randomly (at any time) or at the first void. This will be guided by referring to local guidelines and liaising with the requesting party. Random voids have been proven worthwhile for most test purposes (Delanghe and Speeckaert [53]). However, there are some clinical circumstances where using the first morning void may be essential, including testing for microalbuminuria and spot urine testing to evaluate daily salt intake. This is because the urine has been in the bladder for a reasonably long period, so its composition is independent of daily variations in food and fluid intake and physical activity (Delanghe and Speeckaert [53]).
Indications
Urinalysis is performed for several reasons:
- for screening, prevention and diagnosis of systemic diseases, for example diabetes mellitus, haemolytic disorders, or renal and liver diseases
- for diagnosis of suspected conditions, such as UTIs
- for management and planning, with the aim of ascertaining a baseline and then monitoring the progress of an existing condition and treatment efficacy
- to assess for pregnancy
- to detect the presence of drug metabolites or alcohol
- to assess hydration status (Bickley [18], Provan [167], Wilkinson et al. [215]).
Midstream urine specimens are indicated in adults and children who are continent and can empty their bladder on request (Holm and Aabenhus [84]).
Methods of urinalysis
There are three main methods by which urinalysis is performed:
- urine reagent test strips (dipstick)
- light microscopy
- timed collection (Provan [167]).
Reagent test strips
Before using a reagent strip to analyse a sample of urine, the following observations should be made to support the overall assessment:
- colour
- clarity/debris
- odour (Provan [167]).
See Table 14.12 for further information on visual observations of urine.
Table 14.12 Visual observations of urine and possible indications
| Observation | Possible indications |
|---|---|
| Colour | |
| Green |
Pseudomonas infection, presence of bilirubin
Excretion of cytotoxic agents (e.g. mitomycin) or substances (e.g. methylene blue) |
| Pink/red | Blood |
| Excretion of cytotoxic agents (e.g. doxorubicin) | |
| Orange | Excess urobiliogen or rifampicin |
| Yellow | Presence of bilirubin |
| Brown | Presence of bilirubin |
| Odour | |
| Fishy | Infection |
| Sweet‐smelling | Ketones |
| Debris | |
| Cloudy | Infection, stale urine |
| Sediment | Infection, contamination |
The main advantages of using a urine dipstick are that it is convenient, quick and non‐invasive, with results usually determined in a few minutes (Provan [167]). The main disadvantages are in terms of accuracy, which can be affected by the following factors:
- Bilirubin and urobilinogen are relatively unstable when subjected to light and at room temperature, so it is important to use fresh urine to obtain the most accurate result (Provan [167]).
- Exposure of unpreserved urine at room temperature for a considerable period of time (>4 hours) may result in an increase in micro‐organisms in the urine and a change in pH (Shapiro and Yaney [185]).
- Bacterial growth of contaminated organisms in urine may produce a positive blood reaction (Delanghe and Speeckaert [53]).
- Urine that is highly alkaline may show false‐positive results for the presence of protein (Delanghe and Speeckaert [53]).
- The presence of glucose in urine may reduce its pH as a result of the metabolism of glucose by organisms present in the urine (Delanghe and Speeckaert [53]).
- The presence of urea‐splitting organisms, which convert urea to ammonia, may cause urine to become more alkaline (Trimarchi et al. [200]).
- Certain drugs and chemicals (e.g. meropenem, imipenem, clavulanic acid and nitrofurantoin) can cause false positives due to their influence on the leucocyte reading (Delanghe and Speeckaert [53]). See Table 14.13.
Table 14.13 How drugs may influence the results of reagent stick testing
| Drug | Reagent test | Effect on the results |
|---|---|---|
| Ascorbic acid | Glucose, blood, nitrite | High concentrations may diminish colour |
| L‐dopa | Glucose | High concentrations may give a false‐negative reaction |
| Ketones | Atypical colour | |
| Nalidixic acid | Urobilinogen | Atypical colour |
| Phenazopyridine | Protein | May give atypical colour |
| Ketones | Coloured metabolites may mask a small reaction | |
| Urobilinogen, bilirubin | May mimic a positive reaction | |
| Nitrite | May cause a false‐positive result | |
| Rifampicin | Bilirubin | Coloured metabolites may mask a small reaction |
| Salicylates (aspirin) | Glucose | High doses may give a false‐negative reaction |
Table 14.14 Interpretation of the results (interpretation should always be made with consideration of the whole clinical picture)
| Parameter | Interpretation |
|---|---|
| Specific gravity (relative density) | Usual range: 1.001–1.035; this is a measure of the concentration of the urine and indicates hydration status |
| pH |
Usual range: 6.4–6.8
Urine is usually slightly acidic, but elevated acidity may suggest kidney stones whereas an alkaline result may suggest an infection
Many other factors, such as diet, can also affect pH |
| Leucocytes (white blood cells) |
Usually absent and therefore negative
Present in infection or inflammation of the urinary tract |
| Nitrates |
Usually absent and therefore negative
Present in a bacterial infective process (as produced by bacteria) |
| Protein |
Usually present in small amounts
If the reading is ‘+++’ or more and there is associated haematuria, may indicate infection or damage to renal glomerulus
Proteinuria in the absence of haematuria may indicate high serum albumin levels or tubular damage |
| Glucose |
Usually absent in normal urine and therefore negative
Present in hyperglycaemia (if serum glucose >10–11 mmol/L)
If present without high serum glucose, may indicate renal tubular dysfunction |
| Ketones |
Usually absent and therefore negative
Present in ‘starvation’ states (where the body breaks down fat rather than using glucose for energy)
Ketoacidosis (diabetic/alcoholic)
Poor carbohydrate intake |
| Urobilinogen | Usually present in urine; however, excessive amounts may indicate liver disease |
| Bilirubin |
Usually absent and therefore negative
Positive result may indicate liver disease or an obstructive liver process |
| Blood |
Usually absent or present in very small amounts
Significant presence indicates damage or disease in the urinary tract |
Light microscopy
If a urine dipstick test gives adverse results, further testing may be necessary under laboratory conditions. This may include culture and sensitivity testing to identify organisms responsible for infection and to determine the most effective treatment (Provan [167]).
Optical or light microscopy involves passing visible light transmitted through or reflected from the sample through single or multiple lenses to allow for a magnified view of the sample (Provan [167]). The image generated can then be read and interpreted by the eye, imaged on a photographic plate or captured digitally (Provan [167]). Light microscopy examines the number and types of cells and/or material in the urine and can yield a great deal of information and suggest a more specific diagnosis (Provan [167]). For light microscopy, an MSU should be used as opposed to a fresh spontaneous sample so that any contaminating bacteria in the urethra are flushed out first and thus the sample represents the bladder's contents (Weston [211]). This reduces the chance of contamination of the specimen with epithelial cells, especially vaginal flora (Provan [167]).
Timed urinalysis
Timed urine collection is typically undertaken over an 8‐, 12‐ or 24‐hour period. It simply requires a person to collect their urine in a special container over the set period (Provan [167]). This test typically focuses on renal creatinine clearance, sodium and protein (Provan [167]). Renal clearance refers to the volume of plasma that is cleared of a particular substance in a given time, usually 1 minute, and is tested to determine the glomerular filtration rate, which allows detection of glomerular damage and the examination of the progress of renal disease (Marieb and Hoehn [110]). Timed urinalysis may also examine hormone levels and measure substances such as steroids, white cells and electrolytes; it can also determine urine osmolarity, which makes it a vital test in illnesses such as hyponatraemia and diabetes (Tortora and Derrickson [199]).
