Dear Ministry of Health,

This request is made under the Official Information Act.

It is my understanding PCR tests can be utilised in a way that is qualitative, or quantitative.

Here is a US CDC description of the difference:

>>
A Ct value does not indicate how much virus is present, but only whether or not viral genetic material was detected at a defined threshold. RT-PCR tests can be either qualitative or quantitative, and this affects how a Ct value is interpreted. As of October 23, 2020, all diagnostic RT-PCR tests that had received a U.S. Food and Drug Administration (FDA) Emergency Use Authorization (EUA) for SARS-CoV-2 testing were qualitative tests.

In a qualitative RT-PCR test, known amounts of virus are used during the development of the test to determine what Ct values are associated with positive and negative specimens. A Ct value is generated when testing a patient specimen. The Ct value is interpreted as positive or negative but cannot be used to determine how much virus is present in an individual patient specimen.
In a quantitative RT-PCR test, a range of known numbers of genome copies, called reference samples, are tested alongside each RT-PCR reaction. By comparing the Ct value of a patient specimen to the Ct values from the reference samples, the test can calculate the copy number of target nucleic acid. The correlation between Ct value and viral load can be used in evaluating data from groups of people in categories such as symptomatic or asymptomatic and can be applied to infer the difference in the relative amount of viral load between the two. Although a quantitative RT-PCR test can estimate the level of viral load in a population, a quantitative RT-PCR test cannot determine how much virus is present in an individual patient specimen.
<<

I would like to know if the SARS-Cov-2 PCR testing being conducted in New Zealand is qualitative or quantitative. Or, if it is some combination of the two, or has differed over time (since PCR testing fro SARS-Cov-2 began in NZ), please elaborate on what the situation is.

Yours faithfully,

Mr. Evatt