Why are many more PCR tests coming back void?

The rate of inconclusive results tripled between summer and autumn, while some patients have reported receiving notice of void results that were then rescinded. PublicTechnology investigates.

Credit: Tom Wolf/CC BY 2.0

You may have noticed that taking a coronavirus test is quite in-demand at the moment.

As the omicron variant sweeps through the UK – all while people try to ensure they are virus-free before travelling to see loved ones over Christmas – millions of us are testing ourselves more than ever, both at home using rapid lateral-flow tests and via the PCR tests availale for online ordering and offered at test centres across the UK.

But data shows that, in recent months, an increasing number of those taking the longer and more reliable form of testing have recorded a void result. And PublicTechnology can reveal that some have received notification that their test came back void – only to be told, days later, that a negative result had, in fact, been recorded.

Throughout the month of August, about 1.3 million PCR tests were taken each week across England at testing centres and using at-home kits.

For the first three weeks, the proportion of those tests that came back with a void or unknown result hovered between 1.5% and 1.7%.

It then saw a pronounced rise in the seven-day period that ended on 1 September, when it increased to 2.2% – out of a total of 1.23 million tests taken that week.

The percentage of void results remained steady for a few weeks – before almost doubling overnight during the week ending 22 September: from 2.2% to 4%, in a week where a little over 1.5 million tests were taken.

After some more incremental rises, the rate peaked at 4.6% in the seven days ending 20 October. By that point, the number of PCR tests being taken weekly had risen to 1.87 million; a total of 85,835 of these were recorded as void or unknown results, NHS data shows.

This means that almost one in every 20 tests taken that week failed to record a definitive result.

By mid-November, the rate had fallen to 3.3%. The most recently available set of data – covering the week from 25 November to 1 December – shows a void-test rate of 3%. Some 1.86 million tests were taken during the week.

Although the rate has clearly come down from the peak of a month ago, as of the start of this month it is still double what it was in August. It is also about a third higher than the 2.3% overall void rate for the 91.8 million tests taken in England between 28 May 2020 and 1 December 2021.

PublicTechnology asked the UK Health Security Agency why the proportion might have risen so starkly from August onwards. The agency indicated that, although its data covers the overall number and rate of void tests recorded each week, its reports do not include a breakdown of the reason why.

But it is understood that there are various reasons for which a test could come back as void. These include:

  • the use of an expired test kit
  • missing barcodes
  • samples that arrive later than the five-day validation period
  • damaged or leaking tubes
  • problems with data processing and analysis

UKHSA did indicate that, as the pandemic has progressed, there has been an uptick in the number of tests taken using expired kits that may have been kept in citizens’ homes for some time. In these cases, a void result is recorded before the processing of the sample has even begun.

Though this seems more likely to apply to lateral flow tests, which can be ordered or picked up in multiple packs of seven, rather than PCR tests, which are sent out one at a time, for immediate use.

In all cases, when a citizen receives notice of a void or inconclusive test result, they must take another test, according to UKHSA.

Retracted results
Except: in some cases, people have been sent notification that their recent PCR test came back void – only to receive another message, some time later, informing them that this was not the case.

PublicTechnology has received reports of void test results being, effectively, retracted more than 48 hours after the result had been issued.

The message displayed right – confirming a negative Covid-19 test result – was received early last week; the recipient had originally been contacted over the weekend to inform them that their test had come back void.

In instances where a void result is returned, citizens must take another test, and may also be required to continue to self-isolate, depending on their vaccination status and whether they are symptomatic.

PublicTechnology asked UKHSA why citizens have received incorrect void results, whether they could be attributed to one-off errors or wider issues, and whether anyone that had recorded a positive result had been wrongly told their test was inconclusive.

The agency declined to comment.

As demands on the testing system increase – including reported shortages in the online availability of LFT packs and PCR test slots – unclear results and citizens being unnecessarily asked to retake tests will only add to the pressure.

Authorities will be hoping this void can be filled. 


Sam Trendall

Learn More →

Leave a Reply

Your email address will not be published. Required fields are marked *