What is the Cycle Threshold for PCR Tests Currently Being Used Across Hong Kong?

Allyson van de Pol根據公開資料要求衞生署披露資料

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Dear Department of Health,

What is the current cycle threshold being implemented across Hong Kong for PCR Tests? Is the same CT used across all labs? Are the same CT used for Covid vaccinated and unvaccinated persons?

Yours faithfully,

Allyson van de Pol

Dear Allyson van de Pol,

        Your application dated 1.6.2021 was received.

2.        I regret to inform you that your requested information is not in
our possession.  Therefore, your application cannot be processed.

3.        If we can be of any assistance in the provision of other
information in the future, please contact Ms Sophy KWOK, Executive Officer
(Personnel) 3.  Thank you.

Regards,

(Ms Sophy KWOK)
for Director of Health

顯示引用部分

Dear Department of Health,

Please advise why you do not have such information in your possession? Can you ask the testing laboratories the current cycle thresholds that they are using and have been using since they have started testing for SARS COV-2? Have the thresholds been the same or have they changed over time?

As the Department of Health, this is information that I expect you to have access to and be privy to.

I look forward to your speedy reply.

Yours faithfully,

Allyson van de Pol

Dear Allyson van de Pol,

Thank you for your email on 10.6.2021.

We regret to inform you that your requested information about the
threshold cycle used by the medical laboratories in Hong Kong is not in
our possession.

Below please find some information for your reference.
1. The in-house SARS-CoV-2 RT-PCR assays of Public Health Laboratory
Service Branch at the Centre for Health Protection, Department of Health
have 40 or 45 PCR cycles.
Currently, crossing point, instead of threshold cycle, is adopted by PHLSB
for the SARS-CoV-2 in-house assays.
Please notice that the use of crossing point is different from that of
threshold cycle.

2. Most commercially available SARS-CoV-2 RT-PCR assays have 40 to 50 PCR
cycles.
Some commercially available assays adopt a cut-off Ct (threshold cycle)
/Cp (crossing point) around cycle 36 to determine the test results of
SARS-CoV-2 RT-PCR.
However, the cut-off cycle value shall be validated on-site in the medical
laboratories as the cut-off cycle value(s) is platform-, reagent-lot- and
laboratory testing site-specific.

Yours sincerely,
(CHAN Che-wa)
for Director of Health

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From:        Allyson van de Pol <[FOI #662 email]>
To:        FOI requests at Department of Health <[Department of Health request email]>
Date:        10/06/2021 15:51
Subject:        Internal review of Freedom of Information request - What
is the Cycle Threshold for PCR Tests Currently Being Used Across Hong
Kong?

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Dear Department of Health,

Please advise why you do not have such information in your possession? Can
you ask the testing laboratories the current cycle thresholds that they
are using and have been using since they have started testing for SARS
COV-2? Have the thresholds been the same or have they changed over time?

As the Department of Health, this is information that I expect you to have
access to and be privy to.

I look forward to your speedy reply.

Yours faithfully,

Allyson van de Pol

顯示引用部分

Dear Department of Health,

Thank you so much for your very clear response. Very much appreciated. This leads to a number of follow-on questions that I hope you can help to provide the answers to the following questions:

1. Does the test identify the SARS-CoV-2 virus itself, or only genetic material that could come from the virus?

2. Does a positive PCR test confirm that live virus is present?

3. What is the false positive rate of the assay tests, at the Cp/ Ct that is being used?

4. What is the false negative rate of the assay tests, at the Cp/ Ct that is being used?

5. How were these false positive and false negative rates determined? Please provide details, including what was or were the references.

6. What other non- SARS-CoV-2 genome sequences could yield positives with the assay tests?

Yours faithfully,

Allyson van de Pol

Dear Allyson van de Pol,

Thank you for your email on 20.6.2021.

Please find our reply as below:

Q1.  Does the test identify the SARS-CoV-2 virus itself, or only genetic
material that could come from the virus?
A1:  For RT-PCR, the test detects the genetic material of the virus.

Q2.  Does a positive PCR test confirm that live virus is present?
A2:  No.

Q3.  What is the false positive rate of the assay tests,  at the Cp/ Ct
that is being used?
Q4.  What is the false negative rate of the assay tests,  at the Cp/ Ct
that is being used?
Q5.  How were these false positive and false negative rates determined?
Please provide details, including what was or were the references.
A3 to A5:  The PCR test for SARS-CoV 2 is highly sensitive and specific.
 The sensitivity and specificity of the PCR tests will vary according to
different factors such as disease progress, the PCR platforms and assays
used, type of specimen, quality of specimen and time of specimen
collection.   All preliminary positive PCR results will be further
confirmed by another PCR test targeting different genes of SARS-CoV 2.
Q6. What other non- SARS-CoV-2 genome sequences could yield positives with
the assay tests?
A6:  Some assays may also target SARS-CoV in addition to SARS-CoV 2.  All
preliminary positive PCR results will be further confirmed by another PCR
test targeting specific genes of SARS-CoV 2.

Yours sincerely,
(CHAN Che-wa)
for Director of Health

--------------------------------------------------------------------------

From:        Allyson van de Pol <[FOI #662 email]>
To:        FOI requests at Department of Health <[Department of Health request email]>
Date:        20/06/2021 11:53
Subject:        Re: Internal review of Freedom of Information request -
What is the Cycle Threshold for PCR Tests Currently Being Used Across Hong
Kong?

顯示引用部分

From:        Allyson van de Pol <[FOI #662 email]>
To:        FOI requests at Department of Health <[Department of Health
request email]>
Date:        10/06/2021 15:51
Subject:        Internal review of Freedom of Information request - What
is the Cycle Threshold for PCR Tests Currently Being Used Across Hong
Kong?

--------------------------------------------------------------------------

Dear Department of Health,

Please advise why you do not have such information in your possession? Can
you ask the testing laboratories the current cycle thresholds that they
are using and have been using since they have started testing for SARS
COV-2? Have the thresholds been the same or have they changed over time?

As the Department of Health, this is information that I expect you to have
access to and be privy to.

I look forward to your speedy reply.

Yours faithfully,

Allyson van de Pol

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