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

Critical Care

Compendium