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Appropriate ordering of urine cultures
in older people

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Recent data shows high rates of urine culture testing in older patients

Recent New Zealand primary care data shows that the rate of urine culture test ordering increases significantly in patients aged over 65 years (Figure 1). The diagnosis of urinary tract infection (UTI) can be particularly difficult in older people because of the high rates of asymptomatic bacteriuria, non-specific clinical presentations and the difficulty in collecting good quality urine samples..

Figure 1: Urine culture tests per patient by age
Notes:
Data for the Calendar year 2010.
Data has been excluded where the NZMC number was not recorded.

In this report we look at what might be driving this high rate of testing and consider whether it is appropriate in this group of patients. The aim is to provide practical guidance that helps you to investigate and treat UTIs while avoiding treatment of asymptomatic bacteriuria, which is common but benign in older people. Clinical studies consistently show that treatment of asymptomatic bacteriuria in this group of patients, whether or not accompanied by pyuria, is not beneficial and may be harmful.

Why the high rate of testing?

One explanation can be found in a recent study which addressed the question of clinical presentations of UTI in residents in a long term care facility1. The researchers identified incidents of ‘clinically suspected UTI’ and asked staff the question “What caused suspicion of UTI?” These responses were correlated with urine culture results. The results showed that a wide range of non-specific clinical symptoms were incorrectly identified by staff as due to a UTI. However, almost two thirds of ‘clinically suspected UTI’ had a negative urine culture, suggesting a tendency to over diagnose UTI.

The data contained in Table 1 could suggest the same issue is occurring in primary care in New Zealand. Nationally, in patients aged over 65 years, 1.7 urine cultures are ordered for every one UTI prescription. This rate may be suggestive of indiscriminate testing. Your rate is also provided as by way of comparison.

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Table 1: Urine culture testing in older patients (>65 years)
  Number of urine cultures (2010) Ratio of urine cultures to UTI scripts
You    
National (per GP) 49 1.7
Notes:
Data is for patients aged 65 years and over.
A ‘UTI prescription’ or ‘UTI script’ is defined as a prescription dispensed for either nitrofurantoin, trimethoprim or norfloxacin.

What is the best approach to diagnosis of UTI in older patients?

Ordering urine cultures based on specific signs and symptoms, including specific localising genitourinary symptoms can significantly improve the quality of testing.

An older person with symptoms of dysuria plus either a change in the character of their urine or change in their mental status, has a high likelihood of having bacteriuria and pyuria. Absence of these clinical features identifies people at low risk of having bacteriuria and pyuria1.

Indications for requesting a urine culture in older patients

  • Dysuria
  • PLUS either or both
  • A change in mental status
  • Change in character of the urine

While fever may be associated with UTI in older people, it has a poor predictive value for UTI, as fever can be caused by many other conditions.

The diagnosis of UTI, therefore, should be primarily based on specific symptoms and signs. Tests that suggest or prove the presence of bacteria in the urine may contribute additional information to inform management with the main value of urine culture being to identify bacteria and their sensitivity to antibiotics2.

Consider:

  • Does the number of older people you have requested urine culture for reflect your practice demographic?
  • If the number of cultures is higher than expected, are rest home staff ordering on your behalf?
  • It may be worthwhile discussing with the rest home staff, the importance of the combination of dysuria, and either change in character of urine or change in mental status as an indication for requesting urine culture.

References

  1. Juthani-Mehta M, Quagliarello V, Perrelli E et al. Clinical features to identify UTI in nursing home residents: A cohort study. J Am Geriatr Soc 2009;57: 963–970.
  2. Scottish Intercollegiate Guideline Network 88. Management of suspected bacterial urinary tract infection in adults. July 2006.
    http://www.sign.ac.uk/guidelines/fulltext/88/index.html accessed 14 July 2011