Investigations
1st investigations to order
urinary dipstick
Test
The positive predictive value for a urinary tract infection in patients with nitrites and either blood or leukocyte esterase on urinary dipstick is 92%.[37]
Infection in the setting of obstruction requires prompt intervention.
Result
normal or positive nitrites, leukocyte esterase, and/or blood in presence of infection; microscopic haematuria in renal colic
renal ultrasound
Test
Useful in renal insufficiency or failure to determine whether cause is due to obstructive uropathy.[38] However, in acute obstruction, hydronephrosis may not have had time to develop.[27]
Colour Doppler ultrasound kidneys, bladder, and retroperitoneum can be performed with an abdomen and pelvis x-ray (kidney, ureter, bladder [KUB]) as an alternative to CT. Color Doppler ultrasound allows assessment of twinkling artifact.[39]
During pregnancy, ultrasound is the diagnostic procedure of choice for suspected urolithiasis.[27]
Ultrasound is the initial test for neonates with urinary tract infections to look for hydronephrosis.[32][33]
Result
hydronephrosis affecting the upper urinary tract
urea and creatinine
Test
Elevated creatinine indicates renal damage, but can be reversible. Usually seen with bilateral obstruction or in patients with unilateral obstruction and underlying renal disease.
Result
normal or elevated
FBC
Test
Useful in patients suspected of having infection or in patients with significant haematuria.
Result
normal or elevated WBC if infection present; low haemoglobin and haematocrit if bleeding
CT abdomen and pelvis without contrast
Test
Non-contrast CT abdomen and pelvis is the imaging method of choice in patients with suspected stones.[27]
Result
stones in the urinary tract identified as causing obstruction
Investigations to consider
urine culture
Test
If urosepsis is suspected (fever or hypothermia, leukocytosis or leukopenia, tachypnoea and tachycardia), urine culture should be taken before starting antimicrobial treatment.
Result
may be positive for infection-causing organism
blood culture
Test
If urosepsis is suspected (fever or hypothermia, leukocytosis or leukopenia, tachypnoea and tachycardia), two sets of blood cultures should be taken before starting antimicrobial treatment.
Result
any bacterial growth is considered abnormal
CT scan abdomen and pelvis without and with contrast
Test
A CT scan without and with contrast is recommended if non-contrast CT fails to clearly determine the cause of pain.[27]
Useful for patients with hydronephrosis of unknown cause.
For evaluation of malignancy, oral and intravenous contrast is helpful. Avoid if patient has elevated urea and creatinine levels.
Result
hydronephrosis if upper tract obstruction is present; mass in ureter, pelvis, or bladder may be seen
magnetic resonance urography (MRU)
intravenous pyelogram (excretory urography)
Test
Less sensitive and specific than CT, but excellent anatomical detail. Not recommended if patient has renal insufficiency or contrast allergy.
Result
delayed nephrogram and drainage if obstruction present
nuclear renography (triple renal/MAG3 scan)
Test
Useful for patients with hydronephrosis but unclear diagnosis of obstruction, particularly if asymptomatic, or for triaging patients with small stones.
Result
prolonged T1/2 demonstrates obstruction
voiding cystourethrogram
Test
Useful in children with hydronephrosis to look for posterior urethral valves or ureterocoeles.
Also demonstrates vesico-ureteral reflux, a common cause of non-obstructive hydronephrosis.
Result
demonstrates anatomical abnormalities
bladder ultrasound
Test
Shows evidence of incomplete bladder emptying. If mildly elevated (100-300 mL), suggests poor bladder emptying. If greater than 300 mL, and symptomatic, raises concern for urinary retention.
Result
may be elevated (>100 mL)
prostate specific antigen
Test
Avoid checking in acute retention setting as artificial elevation is common. Check in chronic settings or 3 months after resolution of acute issue.
Result
elevation indicative of prostatic disease
tumour markers (e.g., serum serum carcinoembryonic antigen [CEA], CA125)
Test
Not routinely performed, but if there is suspicion of underlying malignancy, tumour markers such as CEA can be measured.
Result
normal or elevated if underlying malignancy is present
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