Oil Red O Stain on Lung Tissue

Oil Red O Stain on Tissue

The oil red O stain is commonly used to identify exogenous or endogenous lipoid deposits. The stain is done on frozen sections of fresh or formalin-fixed tissue. Tissue from paraffin blocks has had lipoid material removed in the embedding process.

In this section, lipoid-filled macrophages (orange) are present in the alveolar spaces as well as in the interstitium.

Oil Red O Stain on Tracheal Aspirates

In young children, staining of cells from tracheal aspirates with oil red O and finding >50 macrophages with lipoid droplets can be used as a confirmation of suspected aspiration. The lipoid droplets in these cases are small, and whether the lipoid material is exogenous, endogenous, or both remains unknown [1]. Granules in PMNs also stain with oil red O, and these cells must be excluded from the count.

While this study is performed from time to time for children, it is rarely ordered on lung aspirates or lavages from adults, probably because the diagnosis of lipoid pneumonia is rare, and the diagnosis is not considered.


Find an alveolar macrophage with lipoid droplets.

Find 4 PMNs with lipid-staining granules


1. Collins K, Geisinger K, Wagner P, Blackburn K, Washburn L, Block S. The cytologic evaluation of lipid-laden alveolar macrophages as an indicator of aspiration pneumonia in young children. Arch Pathol Lab Med 1995; 119:229-231. Abstract

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Alveolar macrophage with lipoid droplets































PMN with lipid-staining granules