Principles of elimination management
Urinalysis
Learning outcomes
Having read this chapter, the reader should be able to:
Urinalysis is a screening tool commonly used by midwives to identify when further testing is required. While urinalysis may be an effective screening tool, it should not be used in isolation when considering whether or not treatment is required (Steggall 2007). Urinalysis is not sensitive and specific enough to screen routinely for asymptomatic bacteriuria (Awonuga et al 2011); a midstream specimen of urine (MSU) (p. 139) should be obtained for diagnostic purposes if required. This chapter considers the components of ‘normal’ urine, the significance of abnormal findings and the procedure for undertaking urinalysis. Although pregnancy tests can also be undertaken using a specimen of urine, this is not discussed within this chapter.
Definition
Urinalysis is the testing of both the physical characteristics and the composition of freshly voided urine and is undertaken for the purposes of:
• screening: for systemic and renal disease
• diagnosis: of a suspected condition
• management and planning: as a baseline and for planning and monitoring care.
In addition to assessing the physical characteristics of colour, clarity, and odour of urine, urinalysis can be undertaken by laboratory testing or, more commonly and for immediate results, by using a chemical reagent strip. Urine should not be tested if it has stood for 15 or more minutes, as its characteristics may have changed (deWit & O’Neill 2014); thus it is better if the sample is produced at the antenatal clinic rather than bringing one in from home. Leucocytes and erythrocytes tend to precipitate on the bottom of the container and if the sample is not mixed or is left too long the results may be inaccurate.
Composition of urine
Urine has a pH of 4.5–8, specific gravity of 1.005–1.030 and is mainly water (96%) with 4% dissolved substances:
• uric acid, creatinine, sodium, potassium, phosphates, sulphates, oxalates and chlorides
• cellular components, e.g. epithelial cells, leucocytes
• protein and glucose are present in negligible amounts, normally undetectable by routine testing.
Significance of findings
Colour
The colour of urine varies with the specific gravity: concentrated urine is dark yellow in colour whereas dilute urine can appear pale. Urine that is very dark amber or brown–green in colour may contain bilirubin and this should also be suspected if, when shaken, the urine develops yellow foam. Haematuria also alters the colour: dark red if bleeding is within the kidneys or ureters, bright red if bleeding is from the bladder or urethra. Diet and drugs can also influence the colour – rhubarb and beetroot change the urine to a deep red colour, sulfasalazine can result in orange-coloured urine. Pseudomonas infection can give the urine a green colour and dyes such as methylene blue will also alter the colour of the urine (Edmunds et al 2011).
Clarity
Urine is usually transparent or slightly cloudy but when left to stand for several minutes urine becomes cloudy (turbid) due to precipitation of some of the dissolved substances (e.g. uric acid). Proteinuria, bacteriuria and infection may also cause the urine to appear cloudy (Piljic et al 2010). Foamy urine may be due to bilirubin or protein and infection may make the urine seem thick.
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