When the result is positive, it shows how positive it really is.
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What is a positive score?
The ‘positivity score’ is a number that measures how far away from the ‘cut-off value’ the boundary between positive and negative results is. The higher the number, the further away from the cut-off value.
By calculating the positive score, the probability that a positive result is indeed positive can be known to some extent before an amniotic fluid test is performed, and can be used as part of the decision on whether or not to perform an amniotic fluid test.
Cut-off values are reference values set by Illumina for chromosomes 21, 18, 13 and whole region partial deletions and duplications.
Note: The testing healthcare provider will only receive negative or positive results if the test is performed by another laboratory as usual. GeneTech and Verinata Healthcare do not provide numerical data other than positive-negative results to medical institutions. Medical institutions cannot obtain information on the level of positivity even if they inquire. (As of January 2021, according to our own research).
Positive score graphs
Positivity score for Chromosome 21 Number of cases: 44
June 2020~January 2022
● Amniotic fluid test Positive ／
━ Positivity Predictive Value
Positivity score for Chromosome 18 Number of cases: 16
(June 2020~January 2022)
● Amniotic fluid test Positive ／
━ Positivity Predictive Value
Positivity score for Chromosome 13 Number of cases: 6
(June 2020~January 2022)
● Amniotic fluid test Positive ／
━ Positivity Predictive Value
The three tables above show whether pregnant women with positive NIPT test results for chromosomes 21, 18 and 13 trisomy had a positive amniotic fluid test result.
Red dots● refer to those who had a positive NIPT test and a positive amniotic fluid test at the hospital. Blue dots● refer to those who had a positive NIPT test and a negative amniotic fluid test at the clinic.
The further to the right on the graph, the higher the positive score.
Blue dots are more common on the left side (lower positive score), which is a slight false positive.
Due to the nature of the NIPT test, it can only give positive or negative test results.
The positive score is calculated by testing a large number of patients in cooperation with the Tokyo Health Laboratory.
We believe that knowing the degree of positivity helps us to react calmly in the event of a positive test result.
Where your positive score is in the table is a good indication of whether you are really positive or not.
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What is a positive target rate?
The positive predictive value is the probability that a positive diagnosis indicates whether a person is indeed positive. As is well known, the risk of chromosome aberrations increases in proportion to maternal age. Studies have shown that the positive predictive value also increases with maternal age and gestational age. Furthermore, the positive predictive value varies depending on the chromosome being examined.
In other words, from these three factors, it is possible to calculate the positive predictive value of a pregnant woman, i.e. whether she is likely to be really positive if she is diagnosed as positive.
Data from 30,000 (as of December 2022) post-NIPT and amniotic fluid tested pregnant women at Hiro Clinic were collated. The number of patients diagnosed with trisomy 21 by amniotic fluid testing was 30 out of 32 NIPT-positive patients, with a positive predictive rate of 93.75%. Patients with positive amniotic fluid tests for trisomy 18 were 12 out of 16, with a positive predictive value of 75%.3 out of 10 patients with positive amniotic fluid tests for trisomy 13 were positive,with a positive predictive value of 30%.
Everyone says that older births are more risky because
the positive test rate is determined by the age of the mother and the number of weeks of pregnancy.
Positive score report
The results of a NIPT test are diagnosed as positive or negative depending on whether each of the figures obtained by the test exceeds a reference value, known as the ‘cut-off value’. However, if a positive result is obtained with a value just above the cut-off value, the chances of it being negative are naturally very high.
On the other hand, similarly, the positive predictive value is determined by age, gestational week and the chromosomes examined, as mentioned earlier, and if the positive predictive value is closer to the cut-off value but still high, there is a greater chance that the positive diagnosis is indeed positive.
NIPT is a non-confirmatory test; we recommend an amniotic fluid test as a confirmatory test if the NIPT is positive, but many people are unsure whether to have an amniotic fluid test. The positive score and positive predictive value can be used to determine where you are on the scale and whether it is better to have an amniotic fluid test.
Positive score report only attached when positive for chromosome 21 trisomy, chromosome 18 trisomy and chromosome 13 trisomy.
A positive test result does not mean that
you have to immediately apply for an amniotic fluid test.
Think after the positive score report.
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Knowing the positive score can be very useful in these situations.
Pregnant women around 40 years old
When the gestational age is 40 years or older, the positive predictive value is more than 93%. As mentioned earlier, this figure is calculated from the number of weeks of pregnancy and the mother’s age before the test is done.
For example, for a 40-year-old pregnant woman with a 10-week pregnancy, the positive predictive rate for chromosome 21 trisomy is 93.87%.
A positive score in the single digits for this pregnant woman may be negative enough, so it is strongly recommended to wait until the number of weeks when an amniotic fluid test can be performed before making a decision.
Positive Score Report is recommended for
In some cases, a positive positive test score is the only reason to give up. If it is positive, the positive score can help to determine whether an amniotic fluid test should be taken.
Positive score reports for the N-Scan and N-Advance plans are provided free of charge for abnormalities in the number of chromosomes 13, 18 and 21.
※If the test is performed at less than 10 weeks 0 days of pregnancy, no positive target rate, positive score or positive score report is available.
Positive score reports for N-Guard plans are provided free of charge for abnormalities in the number of chromosome 21.
※If the test is performed at less than 10 weeks 0 days of pregnancy, no positive target rate, positive score or positive score report is available.
