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Centre for Evidence-
Based Medicine

Example NNTs - Hematology

Condition or Disorder Intervention vs. Control Outcome Follow-up Duration Event Rates % NNT (95% CI)
CER EER
Reducing venous thromboembolism after elective neurosurgery1 Enoxaparin vs. placebo Pulmonary embolism (PE) or deep venous Thrombosis (DVT) 8 days 33 17 7 (4 to 18)
PE or proximal DVT 14 5 12 (6 to 73)
Overall DVT 32 17 7 (4 to 20)
Proximal DVT 13 5 13 (7 to 143)
Stroke in children with sickle-cell anaemia; periodic blood transfusions2 Transfusion vs. standard care All strokes 20 months 16 2 7 (4 to 18)
Cerebral infarction 15 2 8 (5 to 22)
Idiopathic venous thromboembolism3 Warfarin vs. placebo Recurrent venous thromboembolism 3 months 20.5 1.3 6 (3 to 9)
Total bleeding 1.2 11.4 10 (5 to 30)
Pulmonary embolism and proximal deep venous thrombosis (DVT)4 Subcutaneous low-molecular-weight heparin (tinzaparin sodium) vs. unfractionated heparin (control) Recurrent venous thromboembolism 3 months 6.8 0 15 (8 to 36)
Major bleeding 1.9 1.0 Not significant
Minor bleeding 2.9 1.0 Not significant
Death 8.7 6.2 Not significant

References

  1. N Engl J Med 1998 Jul 9;339(2):80-5
  2. N Engl J Med 1998 Jul 30;339(5):339-40
  3. N Engl J Med 1999 Mar 25;340(12):901-7
  4. Arch Intern Med. Jan 24, 2000; 160: 229-36