MSU midstream specimen of urine, UTI urinary tract infection, CFU colony forming unit
There are approximately one million ER visits per year for suspected urinary tract infection (UTI) in the United States alone. The Centers for Disease Control and Prevention estimate that treatment is inappropriate in at least 40% of cases given antibiotics for UTI.
We can avoid unnecessary antibiotic usage by keeping the following points concerning urinalysis In mind:
1. Abnormal dipstick urinalysis results are very common in nursing home residents in the absence of UTI. At any point in time, up to 50% of all nursing home residents (male and female) will have asymptomatic bacteruria (>100,000 cfu on MSU) irrespective of their level of wellbeing. This will be associated with a positive dipstick urinalysis for white cells and nitrites. Furthermore, the presence of bacteruria in these individuals fluctuates over time. Therefore, if such a patient has findings consistent with UTI on dipstick urinalysis (and even significant growth on MSU culture), we cannot reliably conclude that UTI is the cause of an acute deterioration in their overall status. It should also be no surprise when a nursing home resident has a ‘history of UTIs’. His or her urine may have been tested in the presence of a nonspecific illness in the past and found to be positive. Again, there is a strong possibility that this was incidental. It is worth knowing that the odour and appearance of urine is no guide to the presence of urinary tract infection irrespective of urinalysis findings.
2. Isolated pyuria on dipstick urinalysis (positive for white cells) is never an indication for antibiotic treatment. In hospital practice we are frequently dealing with elderly patients who are unwell with no obvious cause. We are often told that their urinalysis is positive for white cells and negative for nitrites. This has no diagnostic value. Some organisms do not produce nitrates and it is possible for a UTI to be present with negative nitrites on urinalysis.
3. Abnormal urinalysis results must be interpreted in the context of symptoms. As you will see in our illustrative case below, this should probably be point number one! Positive urinalysis results are common in the healthy general female population (even the young) in the absence of significant infection.
4. Diabetes mellitus is associated with an increased prevalence of asymptomatic bacteruria. In the presence of asymptomatic bacteruria, antibiotic treatment has no value in this subgroup.
5. Never let a positive urinalysis result divert you from appropriate investigation. I have seen several disasters resulting from a mistaken diagnosis of UTI (based on urinalysis) as the patients symptoms (often abdominal pain) were ascribed to this cause and a more serious diagnosis was then missed. Keep an open mind if urinalysis is positive.