Urinalysis
Interpreting results
In a normal urine sample there should be no protein, blood or glucose. When interpreting results remember that positive results can have different causes
- Physiological
- Artefactual
- Pathological
Proteinuria
Physiological:
Excessive exercise can produce proteinuria. A phenomenon called orthostatic proteinuria has been reported, whereby after lying flat for prolonged periods proteinuria can occur after standing up.
Artefactual:
This may occur through contamination e.g. from skin commensals
Pathological:
Proteinuria commonly occurs in urinary tract infections. It can also occur in a wide range of renal diseases such as glomerulonephritis or nephrotic syndrome. It can occur during pregnancy as part of a condition called pre-eclampsia.
Further investigations may include:
- Repeat the test strip analysis
- Urinalysis for leucocytes and nitrites
- Midstream urine sample (MSU) for microscopy, culture and sensitivity
- Blood pressure measurement
- Serum urea, creatinine and electrolytes i.e. U&E
Haematuria
Blood in the urine which is detected on a dipstick but which is not visible to the naked eye is called microscopic haematuria.
Physiological/Artefactual:
The most common cause of this in women is menstruation. If you have a positive finding in a female patient it is important to establish if this could be the case.
Pathological:
The most common pathological cause of haematuria is urinary tract infection. Haematuria can also occur in the presence of renal tract calculi (stones), renal of bladder tumours or in other renal diseases such as glomerulonephritis.
Further investigation for haematuria may include:
- Repeat urine test strip analysis
- Urinalysis for leucocytes and nitrites
- MSU for microscopy, culture and sensitivity
- Blood pressure measurement
- Scan/image of bladder/kidney
As the presence of haematuria may indicate malignancy it is important to investigate it fully.
Glycosuria
Physiological:
The kidneys have a certain threshold for glucose and if this is exceeded then glucose will leak into the urine. Some individuals will naturally have a lowered renal threshold for glucose and this can also occur during pregnancy.
Artefactual:
Patients in general practice will often bring in a urine sample if they have any urinary symptoms. Urine should be collected in a sterile container, but contamination may occur if they select a container such as a jam jar or medication bottle leading to falsely high readings.
Pathological:
In diabetes mellitus the serum glucose concentration is raised and therefore the renal threshold is exceeded. This leads to glycosuria.
Further investigation for glycosuria may include:
- Repeat urine test strip analysis
- Check urine for ketones
- Capillary blood glucose testing
- Fasting blood glucose
- Glucose tolerance test