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Prevalence threshold and positive predictive value of noninvasive prenatal testing
Aditi Sivakumar1, Jacques Balayla2
1Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
Summary
Noninvasive prenatal testing (NIPT) shows low positive predictive value for screened conditions because their prevalence is below the calculated prevalence threshold. This indicates NIPT reliability is limited by current disease frequencies.
Area of Science:
- Genetics and Genomics
- Epidemiology
- Reproductive Health
Background:
- Noninvasive prenatal testing (NIPT) has expanded the scope of detectable conditions.
- Despite expanded screening, the prevalence of many NIPT-assessed conditions remains stable.
- The positive predictive value of diagnostic tests is influenced by disease prevalence.
Purpose of the Study:
- To calculate the prevalence threshold for common conditions screened via NIPT.
- To compare calculated prevalence thresholds with actual disease prevalence.
- To evaluate the reliability of NIPT results based on these comparisons.
Main Methods:
- Systematic literature search of six databases and PubMed (2010-2023) for NIPT sensitivity and specificity data.
- Calculation of the prevalence threshold for each condition using a pre-derived epidemiological equation.
- Determination of theoretical test iterations needed to reach the prevalence threshold.
Main Results:
- No NIPT-screened condition met or exceeded its calculated prevalence threshold.
- Trisomy 21 showed the highest concordance between prevalence rate and threshold; Angelman, Cri-du-chat, and Prader-Willi syndromes showed the most significant discordance.
- Most conditions, except Trisomy 21 and XXY, require multiple test iterations to reach their prevalence threshold.
Conclusions:
- The positive predictive value of NIPT is currently low for all tested conditions.
- Disease prevalence levels for NIPT-assessed conditions are significantly below their respective prevalence thresholds.
- NIPT reliability is constrained by the low prevalence of screened conditions.
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