URINE MICROSCOPY AND CULTURE

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Specimen: Midstream or “clean catch” urine, catheter or bladder aspirate specimen, in a sterile container sent to the laboratory immediately, or refrigerated for up to 24 hours.

Method: Phase microscopy of uncentrifuged urine; quantitative cultures, specific identification of significant isolates, antibiotic susceptibility testing.

Application: Dysuria/frequency, cystitis, urinary tract infection, screening in pregnancy, post-partum fever, epididymo-orchitis, unexplained fever. Urine microscopy and culture may not be necessary before commencing treatment in simple urinary tract infections in young women. In this circumstance, a follow-up microurine should be performed 3-5 weeks after treatment is completed, to ensure that asymptomatic relapse has not occurred. Investigation of renal and urinary tract disease and renal involvement in systemic disease.

Interpretation: Cell count: >10 x 10⁶/L pus cells suggests infection; >10 x 10⁶/L red blood cells indicates haematuria. Presence of dysmorphic red cells indicates glomerular origin. Red cell casts may be seen in glomerulonephritis. White cell casts and mixed cell casts indicate renal disease. The presence of granular and/or hyaline casts, as an isolated finding, is of uncertain clinical significance; they may be seen in patients with dehydration. Although crystals are seen frequently, they are not usually of any clinical significance. Presence of >10 x 10⁶/L squamous epithelial cells indicates skin/mucosal contamination of the sample. Infection can be diagnosed in symptomatic patients if bacterial colony count ³10⁶/L (pure growth). The findings on microscopy should also be considered in interpretation. Increased leucocytes and a pure culture favour infection, while increased squamous epithelial cells and mixed culture suggest contamination. In patients without symptoms, “asymptomatic bacteriuria” is defined as a colony count of ³10⁶/L. In catheter or bladder aspirate specimens, any growth indicates infection. Testing for antibacterial activity is commonly performed and will influence interpretation.

Reference: Stamm WE. In: Gorbach SL et al eds. Infectious Diseases. WB Saunders 1992.

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