Minoz et al used the percent of lipid-laden macrophages in a bronchoalveolar lavage (BAL) to identify trauma patients with respiratory failure secondary to fat emboli. The authors are from Universite de Paris Sud and XII.


Patient selection: trauma patient being mechanically ventilated


The BAL is performed within the first 3 days following the trauma.


Method of Corwin and Irwin for counting lipid-laden macrophages (see Chapter 08):

(1) Fluid from a bronchoalveolar lavage is processed with smears prepared for cytology.

(2) The slides are stained for lipid using the oil red O stain.

(3) 100 alveolar macrophages are graded using the following scheme.


Amount of Lipid in the Alveolar Macrophage




one or few intracellular droplets


many distinct intracellular droplets


many confluent intracellular droplets with the nucleus still visible


many confluent intracellular droplets with the nucleus obscured



percent of lipid-laden cells =

= ((number of Grade 3 cells) + (number of Grade 4 cells)) / (number of cells counted) * 100%



• minimum percent of lipid-laden macrophages: 0%

• maximum percent of lipid-laden macrophages: 100%

• Surgical patients without ARDS have a percent <= 5%.

• A percent > 30% supports the diagnosis of the pulmonary fat embolism syndrome.


Differential diagnosis:

(1) Aspiration pneumonia.



• The index has a high negative predictive value (98%) but low positive predictive value (53%). The sensitivity was 89% and specificity 85% (page 978).


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