Combinations of risk factors for ICH to explore their use in diagnostic and management algorithms
| Combination of high-risk factors for ICH used to identify patients for treatment . | Sensitivity, % . | Specificity, % . | Estimated or potential use of combination therapy . | Positive predictive value, % . | Negative predictive value, % . | Number (%) of ITP patients with ICH identified for treatment* . | Number (%) of patients who will test positive but not have an ICH† . | Number of patients without ICH treated per ICH case treated . | Approximate cost of preventing one ICH‡ . |
|---|---|---|---|---|---|---|---|---|---|
| Any bleeding other than skin petechiae and ecchymoses and/or head trauma and/or a platelet count < 10 000/mL | 100 | 23 | Possibly useful | 33 | 100 | 9 (100) | 2944 (77) | 327 | $1.7 million |
| Any bleeding other than skin petechiae and ecchymoses and/or head trauma | 83 | 55 | Probably useful | 41 | 90 | 7.5 (83) | 1727 (45) | 230 | $1.2 million |
| Hematuria and/or head trauma | 50 | 99 | Use in all cases | 94 | 84 | 4.5 (50) | 38 (1) | 8.5 | $45 300 |
| Combination of high-risk factors for ICH used to identify patients for treatment . | Sensitivity, % . | Specificity, % . | Estimated or potential use of combination therapy . | Positive predictive value, % . | Negative predictive value, % . | Number (%) of ITP patients with ICH identified for treatment* . | Number (%) of patients who will test positive but not have an ICH† . | Number of patients without ICH treated per ICH case treated . | Approximate cost of preventing one ICH‡ . |
|---|---|---|---|---|---|---|---|---|---|
| Any bleeding other than skin petechiae and ecchymoses and/or head trauma and/or a platelet count < 10 000/mL | 100 | 23 | Possibly useful | 33 | 100 | 9 (100) | 2944 (77) | 327 | $1.7 million |
| Any bleeding other than skin petechiae and ecchymoses and/or head trauma | 83 | 55 | Probably useful | 41 | 90 | 7.5 (83) | 1727 (45) | 230 | $1.2 million |
| Hematuria and/or head trauma | 50 | 99 | Use in all cases | 94 | 84 | 4.5 (50) | 38 (1) | 8.5 | $45 300 |
The 10 children who presented their ITP with an ICH are excluded from these analyses since their ICH could not be prevented.
These calculations assume an incidence of ICH of 3850 cases/year and that this study captured 50% of true cases of ICH, suggesting an incidence of ICH among children with ITP of 0.3%, that is, 12 cases of ICH per year. As 25% of cases of ICH were the first presenting feature of ITP, we considered 75%, that is, 9 cases of ICH, to be preventable. The number of ITP patients identified for treatment by each combination of risk factors = (9 × specificity).
The number of patients who will test positive by not have an ICH was calculated as (100 − specificity) × (number of children with ICH who do not have ICH, that is, 3850 − 12 = 3838).
This calculation assumes that each child identified as high risk for ICH receives 1 dose of IVIG at 1g/kg and I course of intravenous anti-D at 75 mcg/kg. For average 20-kg child, total cost is $5313.