Modelling the cost-effectiveness of non-invasive prenatal testing in the English sickle cell and thalassaemia screening pathway

BACKGROUND: Sickle cell disease (SCD) and thalassaemia are inherited conditions causing chronic anaemia, increased infection risk and multi-organ failure. Standard of care (SoC) prenatal screening involves carrier blood testing for pregnant women and, if positive, carrier blood testing for biological fathers followed by invasive prenatal diagnosis for pregnancies at risk. Non-invasive prenatal testing (NIPT) presents an alternative pathway which may reduce diagnostic delays and improve equity for pregnant women when the biological father is unavailable by focusing invasive testing exclusively on fetuses shown to have a high risk of SCD by NIPT. This study compares the outcomes of SoC screening with a proposed NIPT pathway replacing the paternal blood testing stage. METHODS: A deterministic decision tree model is used to identify the outcomes of the screening pathways, focusing on the SCD population, from the perspective of the National Health Service (NHS) England. Sensitivity and specificity inputs for NIPT are informed by a separately published minimally acceptable criteria study. Diagnostic outcomes include the number of performed and declined tests and true and false positive/negative diagnoses in each pathway. Economic outcomes include the testing cost of the pathway, the cost per case detected and per accurate diagnosis, and an incremental cost threshold analysis for NIPT. Additional scenario analyses are conducted for the SCD and thalassaemia combined population and for the thalassaemia populations. RESULTS: When considering an overall cohort of 616,573 pregnancies, implementing the NIPT pathway for the screen-positive SCD population results in an incremental cost of £7,584,551. Of 276 prenatal diagnoses (PND) performed in the SoC arm, 76 show a true positive result for SCD, and 2 false positives are identified. In the NIPT arm, there are 6090 NIPTs and 543 PNDs performed, with 213 true positives and 235 false positives identified. The NIPT pathway costs £33,158 more per case detected, and £368 more per accurate diagnosis than SoC; to obtain no incremental cost per case detected versus the SoC, NIPT would need to cost £45.21. CONCLUSIONS: The presented exploratory analysis may gauge the potential cost-effectiveness of introducing NIPT into the screening pathway, pending further research on the technique's diagnostic efficacy.