| Grade 0 | None | No visible iron under high power magnification (×1000) |
| Grade 1 | Very slight | Small iron particles just visible in few reticulum cells under high power magnification (×1000) |
| Grade 2 | Slight | Small, sparsely distributed iron particles just visible under low power magnification (×100) |
| Grade 3 | Moderate | Numerous small iron particles present in reticulum cells throughout the marrow fragment (×100) |
| Grade 4 | Moderate heavy | Larger iron particles throughout the fragment with tendency to aggregate into clumps (×100) |
| Grade 5 | Heavy | Dense, large clumps of iron throughout the fragment (×100) |
| Grade 6 | Very heavy | Very large deposits of iron, both intra- and extra-cellular, obscuring cellular detail in the fragment (×100) |