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The page below is a sample from the LabCE course Reading and Reporting Gram Stained Direct Smears. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Size and Appearance of Nonbacterial Cellular Elements on Gram Stained Smears

Type of Cell Average Size Image Comments
Epithelial cells 25 µm
  • Appear pink/red on Gram stained smear.
  • Larger than white blood cells.
  • Have a single nucleus.
  • They are an indication of a suboptimal or unacceptable specimen if present in large numbers in sputum specimens, tracheal or endotracheal aspirates, or in urine specimens.
White blood cells 12 µm
  • Appear pink/red on Gram stained smear.
  • Most often, polymorphonuclear white blood cells (PMNs).
  • White blood cells indicate inflammation and possible infection.
  • The direct smear examination should focus within and around these cells.
Hyphae/pseudohyphae Varies
  • Appear blue on Gram stained smear.
  • Hyphae are tubular filamentous fungal elements, which may show branching or intertwining.
  • Pseudohyphae are multiple buds of yeast that do not detach, thereby forming chains.
Yeast 7 µm
  • Appear blue on Gram stained smear.
  • Round to oval, often budding. About the same size as red blood cells.
  • Generally much larger than bacteria.
  • A few yeast may be present as normal flora in upper respiratory tract or genital tract. They may be significant if they predominate, or if budding yeast forms are seen.
Red blood cells 7µm
  • Appear red on Gram stained smear
  • Not usually considered a significant finding.