The sensitivity of dipstick haematuria for detecting ureteric stones presenting acutely is in the order of 95% on the first day
3. NONTRAUMATIC RENAL EMERGENCIES 19
of pain, 85% on the second day of pain, and 65% on the third and fourth days (Kobayashi et al. 2003). Dipstick testing is slightly more sensitive than urine microscopy for detecting stones (80% versus 70%), and both ways of detecting haematuria have roughly the same specificity for diagnosing ureteric stones (about 60%). The slightly greater sensitivity of dipstick testing over microscopy reflects the fact that seeing red blood cells depends on how good the technician is at looking for them, and that they lyse, and therefore disappear, if the urine specimen is not examined under the microscope within a few hours. Thus, if you see a patient with a history suggestive of ureteric colic, and their pain started 3 to 4 days ago, they may well have no blood detectable in their urine even though they do have a stone.
The relatively poor specificity of dipstick or microscopic haematuria for detecting ureteric stones reflects the multiple other pathologies that can mimic the pain of a ureteric calculus combined with the fact that blood is detectable in a proportion of patients without demonstrable urinary tract pathology; in fact, no abnormality is found in approximately 70% of patients with microscopic haematuria, despite full investigation with cystoscopy, renal ultrasound, and intravenous urography (IVU) (Khadra 2000). Thus, blood in the urine may be a completely coincidental finding in a patient who presents with flank pain due to a non-stone cause.
Perhaps the most important aspect of examination in patients with a ureteric stone confirmed on imaging is to measure their temperature. If patients have a stone, and they have a fever of, say, 39°C, they may well have infection proximal to the obstructing stone. A fever in the presence of an obstructing stone is an indication for urine and blood culture, intravenous fluids and antibiotics, and nephrostomy drainage if the fever does not resolve within a matter of hours of commencement of antibiotics.