8.5: Special Investigations
- Page ID
- 15616
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- Mid stream urine examination for infection and haematuria.
- Post micturition residual volume. For a long time, a residual volume of 100ml was considered to be cut off point for normality, however more recently it has been suggested that any residual volume over 30ml might be associated with urinary tract infection. Residual volumes can be measured either by catheterisation or ultrasound scanning. Ultrasound scanning is less invasive and causes less discomfort than urinary catheterisation. It is important to remember however that the accuracy of this measurement depends on the time since the last passage of urine until the time of the measurement of the residual volume.
- Uroflowmetry is an excellent non invasive screening test for voiding dysfunction. A flow rate of less than 15ml per second would be considered to be abnormal. This flow rate however also needs to be compared to the voided volume and the Liverpool Nomogram, plotting flow rate against voided volume, is used for this purpose.
- Uro-dynamic studies. If the diagnosis of voiding dysfunction has been made, uro-dynamic studies are important for confirmation of this diagnosis and to assess whether the voiding dysfunction is associated with poor detrusor contractions or obstruction, associated with high bladder pressures of more than 20cm H2O with maximum flow of less than 15ml/sec.
- Imaging of the bladder and lower urinary tract by means of ultrasound or videocystourethrography can also be used.
- Other simple non invasive investigations could include voiding diaries and frequency and volume charts kept by the patient.