When is an MSU indicated

Urine microscopy, culture and sensitivity is required in patients (1,2) -

• 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 (1)
• a bacterial count of >=10^5 is generally regarded as significant bacteriuria (2). 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)

With respect to adults in primary care more detailed guidance is now available (3):

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Reference:

• 1. Health Protection Agency (HPA) 2009. Diagnosis of UTI - Quick reference guide for primary care
• 2. Health Protection Agency (HPA) 2009. National standard method. Investigation of urine
• 3. Public Health England (August 2019). Diagnosis of urinary tract infections Quick reference tool for primary care for consultation and local adaptation