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CLIA CCC study materials
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CLIA CCC: Urinalysis and Body Fluids

CLIA CCC · Work through your exam, one topic at a time.

All guide sections

Urinalysis and Body Fluids

What this domain tests

This domain covers specimen handling, dipstick chemistry, microscopy, and the analysis of CSF, serous fluids, synovial fluid, semen, and amniotic fluid. Questions typically give a result set and ask what it means or what artifact explains it.

Urine

  • Analyze within about 2 hours at room temperature or refrigerate; refrigeration precipitates amorphous urates and phosphates and can alter pH, so warm and mix before microscopy.
  • Dipstick protein uses the protein-error-of-indicators principle and is falsely positive in strongly alkaline urine or after some contrast dyes; it detects albumin poorly for globulins and Bence Jones protein.
  • Blood is detected by pseudoperoxidase activity: false positives with hypochlorite, false negatives with ascorbic acid. Leukocyte esterase and nitrite support urinary tract infection but nitrite requires nitrate-reducing organisms and adequate bladder dwell time.
  • Microscopy: report RBCs, WBCs, epithelial cells, casts, and crystals per high-power field. Dysmorphic RBCs and red cell casts indicate glomerular bleeding; squamous cells indicate contamination.

Body fluids

  • CSF: cell count and differential, protein, glucose (CSF-to-serum ratio normally about 0.6), lactate, Gram stain and culture. Correct the WBC for a traumatic tap by subtracting roughly 1 WBC per 500–1000 RBCs, but do not rely on this alone.
  • Serous fluid: Light's criteria classify an exudate when any one of the following is met - fluid-to-serum protein ratio above 0.5, fluid-to-serum LDH ratio above 0.6, or fluid LDH above two-thirds the upper normal serum LDH.
  • Synovial fluid: WBC below 2000/µL is noninflammatory, above 50,000/µL suggests septic arthritis. Monosodium urate crystals are needle-shaped and negatively birefringent; calcium pyrophosphate crystals are rhomboid and positively birefringent.

Worked example

Pleural protein 4.2 g/dL with serum protein 7.0 (ratio 0.60); fluid LDH 300 U/L with serum LDH 180 (ratio 1.67); upper normal serum LDH 200, so the two-thirds threshold is 133. All three criteria are met, so the fluid is an exudate. Reasoning: one criterion is sufficient. Beware that diuresis can make a transudate look exudative.

Traps that cost marks

  • Squamous contamination inflating the WBC count.
  • Reading a refrigerated, unremixed sample.
  • A protein dipstick read on alkaline urine.
  • Confusing urate with uric acid crystals.
  • Applying adult CSF protein reference limits to a neonate.