How do you check for fat globules in urine?

How to Check Urine Fat Globules

To check for fat globules in urine, use polarized light microscopy on a fresh urine sample, which will reveal characteristic Maltese cross patterns when fat is present. This technique is essential for identifying lipiduria, which can be an important diagnostic finding in various conditions including nephrotic syndrome and Fabry disease.

Sample Collection and Preparation

1. Collect a fresh urine specimen
2. Centrifuge the urine to separate it into:
   • Lower cellular fraction (containing oval fat bodies)
   • Upper noncellular fraction

Microscopic Examination Technique

Standard Microscopy

• Examine the sediment under standard light microscopy first
• Look for oval fat bodies (cells laden with lipid droplets)

Polarized Light Microscopy

• Switch to polarized light microscopy
• Identify birefringent (anisotropic) droplets that display characteristic Maltese cross patterns
• These patterns are highly specific for lipid content

Interpretation of Findings

Normal Findings

• Small amounts of lipid may appear in urine under normal circumstances 1
• Absence of oval fat bodies and anisotropic droplets

Abnormal Findings

• Presence of oval fat bodies containing anisotropic droplets
• Maltese cross patterns under polarized light
• In nephrotic syndrome, these droplets are primarily composed of cholesterol esters 2

Clinical Significance

• Significant lipiduria is associated with:
  • Nephrotic syndrome (most common cause)
  • Fabry disease (distinctive Fabry bodies with specific Maltese cross patterns) 3
  • Fat embolism syndrome 4
  • Chyluria
  • Trauma to fatty tissues near urinary tract 5

Advanced Analysis (If Required)

For more detailed characterization:

• Ultracentrifugation (48,000 × g for 2 hours) can separate the noncellular fraction into supernate and infranate fractions 2
• Gas-liquid chromatography can determine fatty acid composition
• Agarose gel electrophoresis can identify alpha-migrating lipid bands

Clinical Pearls

• The shape of Maltese cross-bearing bodies can distinguish conventional fat particles from Fabry bodies with high sensitivity and specificity 3
• Urine specimens with anisotropic droplets typically have higher total cholesterol excretion (mean 35.5 mg/L vs 8.7 mg/L in specimens without) 2
• Heating the specimen can help identify cholesterol esters, which undergo phase transitions at characteristic temperatures (mean 41.3°C) 2
• Polarized light microscopy is a cheap, rapid tool for screening subjects suspected of having Fabry disease or nephrotic syndrome 3

Common Pitfalls

• Delay in examination can lead to degradation of lipid structures
• Failure to use polarized light microscopy will miss the characteristic Maltese cross patterns
• Confusing other birefringent materials with fat globules
• Not correlating findings with clinical context and other laboratory parameters

Examining urine for fat globules using polarized light microscopy is a valuable diagnostic tool that can provide important clues to underlying renal and metabolic disorders when properly performed and interpreted.