UTI in a woman (diagnostic comparison of urine dipstick versus symptoms)

A review of evidence examining the sensitivity of symptoms in predicting a UTI in females found that (1):

• Four symptoms and one sign significantly increased the probability of UTI:
  • dysuria
  • frequency
  • haematuria
  • back pain
  • and the sign costovertebral angle tenderness
    
• Four symptoms and one sign significantly decreased the probability of UTI:
  • absence of dysuria
  • absence of back pain
  • history of vaginal discharge
  • history of vaginal irritation
  • and the sign vaginal discharge on examination
    
    
• of all individual diagnostic signs and symptoms, the 2 most powerful were history of vaginal discharge and history of vaginal irritation, which significantly decreased the likelihood of UTI when present
  
  
• one study examined combinations of symptoms, and the resulting likelihood ratios(LRs) were more powerful
  
  • the highest likelihood ratio for the combination of dysuria and frequency but no vaginal discharge or irritation
  • one study of patients with recurrent UTI found that self-diagnosis significantly increased the probability of UTI
    
    
• the authors concluded that "..in women who present with 1 or more symptoms of UTI, the probability of infection is approximately 50%. Specific combinations of symptoms (eg, dysuria and frequency without vaginal discharge or irritation) raise the probability of UTI to more than 90%, effectively ruling in the diagnosis based on history alone.....in contrast, history taking, physical examination, and dipstick urinalysis are not able to reliably lower the post-test probability of disease to a level where a UTI can be ruled out when a patient presents with 1 or more symptoms..."

A more recent systematic review concerning diagnosis of UTIs in females found (2):

• dysuria, frequency and urgency have a higher sensitivity than specificity and are more useful in ruling out a UTI diagnosis
• haematuria has a higher specificity than sensitivity and is more useful in ruling in a diagnosis of UTI
• combining positive dipstick test results, particularly tests for nitrites, with symptoms increases post-test probability of a UTI. In particular, presence of haematuria combined with a positive dipstick test result from 75.8% to 93.3%
• presence of dysuria combined with a positive dipstick test result for nitrites increases post- test probability from between 51.1% to 82.2%

Therefore in conclusion:

• if there are one or more symptoms of a UTI present and there is a negative dipstick then a UTI cannot be ruled out
  • there is study evidence to suggest the likelihood of a UTI is about 50% if one or more symptoms are present
• dysuria, frequency and urgency have a higher sensitivity and are the most useful symptoms in ruling out a diagnosis of a UTI
• the presence of haematuria is the most specific symptom for ruling in a diagnosis of a UTI
• the likelihood of a proven UTI is significantly increased if there is a positive dipstick test for nitrites in the presence of dysuria and/or haematuria

References:

1. Bent S et al. Does this woman have an acute uncomplicated urinary tract infection? JAMA. 2002 May 22-29;287(20):2701-10.
2. Giesen LG et al. Predicting acute uncomplicated urinary tract infection in women: a systematic review of the diagnostic accuracy of symptoms and signs.BMC Fam Pract. 2010 Oct 24;11:78.