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Sally Mandour: Bone Marrow Needle Gauge Explained
Sally Mandour/LinkedIn
Sep 22, 2026, 08:42

Sally Mandour: Bone Marrow Needle Gauge Explained

Sally Mandour, Associate Professor, Head of Hematology Unit at Clinical Pathology Department of National Liver Institute, Monofeya University, shared a post on LinkedIn:

“Bone marrow needle size!!

Did you know what those numbers on a bone marrow needle actually mean?

Most of us glance at ’11G’ or ‘3.00/2.20 mm’ on the packet and just grab the needle on the tray.

But those numbers are the difference between a clean diagnostic core and a fragmented, non-representative sample.

The Gauge:

The rule is that the smaller the gauge number, the larger the needle.

An 11G needle is thicker and more rigid than an 18G – the opposite of what most people assume.

Take an example,, size of a bone marrow biopsy needle reads as:

  • 11G – 3.00/2.20 × 100 mm (shown in images).
  • 3.00 mm is equal to outer diameter (cannula).
  • 2.20 mm is equal to inner diameter (stylet).
  • 100 mm is equal to whole length.

Selection isn’t one-size-fits-all – it changes with age:

  • Neonates or Infants:
    18-20G aspiration (approximately 1.2-0.9 mm), 20-25 mm – biopsy rarely needed.
  • Pediatric (1–10y):
    16-18G aspiration (approximately 1.4-1.2 mm) | 15-16G biopsy (approximately 1.8-1.6 mm), 50-70 mm.
  • Adolescents or Adults:
    15-18G aspiration (approximately 1.8-1.6 mm) | 11-13G biopsy (3.00-2.40 mm), 70-100 mm.”

Sally Mandour

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