| Enrichment Factor (EF) | Categories |
| EF < 2 | Deficiency to minimal enrichment |
| 2 ≤ EF < 5 | Moderate enrichment |
| 5 ≤ EF < 20 | Significant enrichment |
| 20 ≤ EF < 40 | Very high enrichment |
| EF ≥ 40 | Extremely high enrichment |