Laboratory Urinalysis

Laboratory urine analysis

Microscopy

  • Uncentrifuged specimen
  • Examine for red cells, white sells and epithelial cells
  • Pyuria (>10 x 106 /L) indicative of the presence of inflammation
    • Pyuria is usually, but not always associated with significant bacteruria
    • White cells can be associated with non-infectious conditions such as calculus, renal disease, trauma and neoplasia

Casts

  • Plugs of High MW mucoprotein form in the renal tubules and collecting ducts by agglutination of protein cells or cellular debris and flushed loose by urine flow
  • Hyaline
    • Normal if present in small amounts
    • Inflammation, trauma to glomerular capillary, renal parenchymal disease
    • Epithelial
      • Eclampsia, amyloidosis, heavy metal poisons
      • Renal tubular damage and nephrosis
      • Granular
        • Coarse or fine
        • Lead poisoning, ARF, CRF, PN
      • Fatty/waxy
        • Nephrotic, diabetes, CRF
      • RCC
        • GN, SLE, SBE, renal infarction
        • Malignant HT, collagen disease, sickle cell
      • WCC
        • Acute PN and GN
        • Lupus nephritis
      • Drugs
        • Contrast, amphotericin, isoniazid, frusemide, penicillin, sulphonamides, gentamicin, Bactrim

Culture

  • Urine in the bladder is normally sterile
  • In process of specimen collection contamination from urethra and periurethral areas is common
  • Count significance (Significant bacteruria)
  • Must take age, sex, clinical history into account
  • Generally accepted that >108 bacteria per litre is indicative of significant bacteruria
  • PPV >98%
  • NPV < 65%
  • 33% of acutely symptomatic females have bacterial counts below this (significant bacteruria taken as 105 in these people)

Sensitivity and specificity of microbiology tests

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