Estimated number needed to test to prevent VTE when not taking combined oral contraceptives
| Thrombophilia . | Risk on COC per year, % . | Risk difference per 100 women . | Number not taking COCs to prevent 1 VTE . | Number of relatives to be tested . |
|---|---|---|---|---|
| Family history of VTE | ||||
| General population, no family history | 0.08 | 0.03 | 3333 | None |
| General population, family history | 0.04 | 0.06 | 1667 | None |
| Relatives with FVL or PGM | 0.5 | 0.3 | 333 | 666 |
| Relatives with AT, PC, or PS deficiency | 4.3 | 3.6 | 28 | 56 |
| Thrombophilia . | Risk on COC per year, % . | Risk difference per 100 women . | Number not taking COCs to prevent 1 VTE . | Number of relatives to be tested . |
|---|---|---|---|---|
| Family history of VTE | ||||
| General population, no family history | 0.08 | 0.03 | 3333 | None |
| General population, family history | 0.04 | 0.06 | 1667 | None |
| Relatives with FVL or PGM | 0.5 | 0.3 | 333 | 666 |
| Relatives with AT, PC, or PS deficiency | 4.3 | 3.6 | 28 | 56 |
Table adapted with permission from Middeldorp,50 which includes data based on family studies and a general population risk based on a baseline VTE risk in young women of 0.01% per year, an RR of VTE by use of COC of 4, and an RR of 2 for VTE by having a positive family history.