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The diagnosis is difficult in older patients since the likelihood of asymptomatic bacteria is higher as patients gets older (1).

  • in primary care - in a woman with uncomplicated cystitis urinary culture is not necessarily required, with nitrite and leucocyte tests being adequate (2)
  • urine microscopy, culture and sensitivity - this is required in patients with recurrent or complicated infections, during pregnancy, in suspected pyelonephritis, in men

Urine dipstick:

  • used in women with minimal signs and symptoms (two symptoms or less)
  • a negative test does not rule out bacteriuria (1) Laboratory investigations of UTI usually include microscopy and quantitative culture (3)

Urine microscopy, culture and sensitivity is required in patients -

    • with recurrent or complicated infections
    • during pregnancy
    • in suspected pyelonephritis (temp >=39.4; rigors; nausea; vomiting; diarrhoea; loin pain or tenderness)
    • in men
    • suspected UTI in children, any sick child and every young child with unexplained fever
    • catheterised patients: Send sample only if features of systemic infection, as bacteriuria is usual
    • abnormalities of genitourinary tract
    • failed antibiotic treatment or persistent symptoms
    • in elderly patients presence of two signs of infection (especially dysuria, fever >38 or new incontinence) is needed before taking a sample (2)
  • a bacterial count of >=10^5 is generally regarded as significant bacteriuria (3) but in men with signs and symptoms of UTI, a count of >=10^3 (with 80% of the growth is of one organism) is sufficient for the diagnosis (1). The health protection agency has issued the following colony counts as diagnostic values:
    • culture of single organisms >=10^4 colony forming units (CFUs)/mL + urinary symptom
    • >=10^3 CFU/mL of Escherichia coli or Staphylococcus saprophyticus (2)

Further investigations may be indicated if there are recurrent UTIs in a woman e.g. ultrasound, IVU. A child with a single episode of urinary tract infection previously required referral for specialist investigation but now the criteria for referral for investigation depends on other factors (see linked item).

With respect to UTIs in a man then further investigation/referral depends on various factors (1,2,3)

  • referral for assessment is not routinely indicated
    • however, referral for assessment should be considered for men who have:
      • symptoms of upper urinary tract infection (pyelonephritis) (1)
      • failure to respond to appropriate antibiotic therapy (1)
      • frequent episodes of urinary tract infection (UTI) - this is stated as two or more episodes in a 3-month period (1)
      • features of urinary obstruction (e.g. in older men, enlarged prostate)
      • history of pyelonephritis, calculi, or previous genitourinary tract surgery
    • urgent referral is indicated for men with suspected cancer
      • any age with painless macroscopic haematuria:
        • if haematuria is associated with symptoms of UTI
          • culture the urine before referring
          • if UTI is not confirmed by urine culture, or if haematuria does not resolve with treatment of the UTI
            • refer urgently
      • recurrent or persistent UTI associated with haematuria, in a male aged 40 years or older
      • unexplained microscopic haematuria, in a male aged 50 years or older
      • with an abdominal mass identified clinically or on imaging that is thought to arise from the urinary tract

It has been proposed that the first-line investigations for a UTI in a man should be an ultrasound and a plain abdominal X-ray (4). In a study by the authors ultrasound was more effective at identifying incomplete bladder emptying than IVU. Men with this problem went on to have flow studies. Ultrasound is not as effective as an IVU at detecting renal tract stones but the addition of a plain X-ray solves this problem.

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