The proportion of patients who are diagnosed correctly as positive or negative, respectively
| Positive predictive value (PPV)
|Negative predictive value (NPV)*|
|The likelihood that a screened positive pregnancy, is truly affected with a trisomy.||The likelihood that a screened negative pregnancy, really doesn't have a trisomy.|
|What does it mean for the pregnancy?||The high IONA® PPV implies that the false positive results are minimised (unaffected fetus tested positive); meaning less unnecessary diagnostic procedures are required.||The high IONA® NPV implies that the false negative results are minimised (affected fetus tested negative), meaning fewer syndromes are being missed.|
|The IONA® test||Sensitivity (Detection or True Positive Rate)||False Negative Rate (FNR)||Specificity (True Negative Rate)||False Positive Rate (FPR)||Accuracy|
|The proportion of truly affected pregnancies that screen positive||The proportion of pregnancies that have the syndrome but have screened negative||The proportion of truly unaffected pregnancies that screen negative||The proportion of pregnancies that do not have the syndrome but have screened positive.||The likelihood that a fetus will have a true screening result (true negative or true positive).|
|Trisomy 21 (Down’s syndrome)||99.84%||<0.001%||99.98%||0.022%||99.98%|
|Trisomy 18 (Edwards’ syndrome)||97.22%||0.014%||99.99%||0.0125%||99.98%|
|Trisomy 13 (Patau’s syndrome)||100%||<0.001%||100%||<0.001%||>99.99%|
Fetal Sex Determination
If specifically requested, the IONA® test is able to identify whether the fetus is genetically male or female based on cell-free DNA extracted from the maternal plasma.
The sex determination test has an accuracy evaluated at >99% for singleton and monochorionic twin pregnancies. The IONA® test is not suitable for dichorionic twin pregnancies as the fetal gender of each individual twin cannot be determined.
Discordances between phenotypic and genotypic fetal sex assessed by the IONA® cfDNA analysis may potentially arise with technical failure or very rare biological conditions (such as vanishing twin, sex chromosomal abnormalities, etc.…).
A ‘Sex Determination Failure’ result may be reported if there is insufficient data to support the sex determination analysis. This is separate from the trisomy analysis and does not reflect on the quality of any other result generated by the IONA® test.
The IONA® test has a re-draw rate of <0.5%.
The IONA® test is a CE marked in vitro diagnostic product and as such the IONA® clinical validation study(1) has formed part of the Technical File that has been reviewed by a Notified Body. A recent independent study(2) performed at Kings College, London showed the IONA® test detected 100% of the trisomies, with 0% false positives, present in the 242 blinded maternal blood samples.
IONA® test publications - open access
- Ultrasound Obstet Gynecol. 2015 Oct 23. DOI: 10.1002/uog.15791. Clinical evaluation of the IONA® test: a non-invasive prenatal screening test for Trisomy 21, 18 and 13. Papageorghiou A, Khalil A, Forman M, Hulme R, Mazey R, Mousa HA, Johnstone ED, McKelvey A, Cohen KE, Risley M, Denman W, Kelly B.
- Ultrasound Obstet Gynecol. 2015 Dec 28. DOI: 10.1002/uog.15749. The IONA® test for first-trimester detection of trisomy 21, 18 and 13. Poon LC, Dumidrascu-Diris D, Francisco C, Fantasia I, Nicolaides KH.
- Fetal Diagnosis and Therapy. 2017 Feb 8. Doi: 10.1159/000455025. The IONA® Test: Development of an Automated Cell-Free DNA-Based Screening Test for Fetal Trisomies 13, 18, and 21 That Employs the Ion Proton Semiconductor Sequencing Platform. Crea F, Forman M, Hulme R, Old R.W, Ryan D, Mazey R, Risley M.D
|June 2016||Side-by-side comparison of the NIFTY test and IONA® test for Non-Invasive Prenatal Testing (NIPT)||FMF World Congress|
|July 2016||the IONA® test - update on dynamic Fetal Fraction||ISPD 2016|
|March 2017||Bridging the non-invasive prenatal testing gap: accessing private screening in an NHS teaching hospital||BMFMS 2017|
|June 2017||Use of Maternal Age or First Trimester Screening risk results in the estimation of trisomy risk in an NIPT||FMF 2017|
|April 2018||THE SAFE TEST: Performance of non-invasive prenatal screening (NIPS) for high-risk pregnancies in the Southwest Thames Region||BMFMS 2018|
* Clinical Performance of the IONA® test in over 20,000 patient samples