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

References and Links

• Urine Color
• Urine Transparency (turbidity)
• Dipstick urinalysis
• CCC – Urinalysis
• Laboratory Urinalysis
• Urinalysis Overview Table
• Urine electrolytes – Urinary anion gap