Pluslife FAQ (EN)

This website is a private, non-commercial knowledge base. It is not intended for the general public and makes no claim to completeness, accuracy or being up-to-date. It can in no way replace a consultation with qualified medical personnel.

Pluslife is a commercial, molecular LAMP assay for the detection of SARS-CoV-2 RNA. It is similar to (but much cheaper than) devices like Lucira or Cue, which are only available on the US market.

Costs are about ~5-7€ per test and 150-300€ for the device itself. It is the only affordable molecular Covid test procedure currently available in Germany.

The tests are very simple to use, but require careful work and some attention to detail. They're officially meant for lab usage. Use them outside the professional environment at your own risk.

To perform the test correctly, it is sufficient to work exactly according to the instructions supplied by Pluslife - they're very instructive. We recommend wearing protective gloves. This website is intended to provide background information only, you don't have to read it to use the tests successfully.

Sensitivity

The manufacturer specifies a 95% LOD ("Limit of Detection") of 400 copies/mL. The LOD is the lower limit of sensitivity: a sample containing 400 viral RNA copies per mL was correctly detected as positive in 19 of 20 samples when tested by the manufacturer.

This is an excellent result and is within the range of lab PCR tests, which typically have LODs between 50 and 1000 copies/mL, depending on the quality of the PCR assay.

For comparison: a rapid antigen test requires millions to tens of millions of RNA copies/mL, multiple orders of magnitude worse! Here is an attempt to represent these huge quantities as cube volumes:

Unlike rapid antigen tests, Pluslife tests have a good chance of detecting an infection before the viral load is high enough for infection.

Molecular tests such as Pluslife offer a high degree of certainty and can enable social interactions that would otherwise be too risky.

How to buy

Device and tests are sold by Altruan. For non-commercial use, Altruan worked with us to offer special conditions to our community - email us for details (hi [ät] virus.sucks).

Altruan is the only importer in Germany, everyone else buys from them.

This website is private, independent and non-commercial. We do not receive any compensation.

Hexamed

Hexamed also sells Pluslife devices and test kits. However, we recommend avoiding Hexamed, since the store website contained malware for an extended period of time at the end of August 2023 and redirected visitors to malicious third-party websites.

The problem has since been resolved, but privacy and security concerns remain: it is problematic that the site was hacked in the first place and that customers were not informed, and the fix took far too long. It is unclear what measures the operator has taken to prevent future hacks.

They will also call you on your phone to sell you more tests or gloves.

Tips and tricks

Risk of DNA contamination

The manual mentions several times the danger of "contamination". Don't worry!

The LAMP method, on which the Pluslife tests are based, is based on the exponential amplification of target gene sequences. The viral RNA is first converted to DNA (reverse transcription) and the target sequences - if present - are then amplified with a polymerase enzyme. A few RNA copies end up becoming billions of DNA copies, which can then be easily detected using an optical method.

However, this also means that the test card eventually contains very high quantities of these DNA snippets. While they are harmless and not infectious, they can still cause issues.

The procedure is very sensitive and even the smallest amounts of post-amplification DNA ("amplicons") are sufficient to contaminate subsequent reactions, which then leads to false positive results.

DNA is very robust, cannot be removed with normal disinfectants and only degrades very slowly. Decontamination requires special laboratory cleaning agents, strong UV light or hydrogen peroxide solution, none of which are particularly appealing outside (or even inside) a lab environment.

This is why the test card should never be opened after the reaction. As long as you do not damage the card and keep the lid on, there's no risk of contamination!

Handle positive tests with extra care, remove positive test cards with protective gloves and dispose of them immediately in one of the plastic bags provided.

By the way: In proper PCR labs, a negative control ("No Template Control") is always performed alongside the normal tests to detect carryover contamination. There are also different methods for PCR to remove DNA from the first step of the reaction before transcription. With Pluslife, however, all reaction chambers contain the same liquid, so it's not possible to run a negative control alongside a reaction.

If a positive test card leaks, false positives should be expected in the future. If possible, dispose of all objects that have come into contact with the liquid. Use disposable gloves and do not touch any other objects. Avoid contact with bare hands. Wash very thoroughly if you somehow miraculously do get it on your skin.

False positive results

Pluslife tests have very high specificity. While false positive results are possible, they are very unlikely and are usually due to DNA contamination in the environment. While not unheard of in lab environments, it's extremely unlikely to be a problem at home.

However, we have seen some cases of false positive results due to processing errors. In these cases, the false positive result was displayed much too quickly within the first few minutes after the start of the test.

The cause is unclear, but a probable explanation is air bubbles that move inside the test card due to the heat and thus cause a sudden increase in the optical signal, which the device then incorrectly detects as a positive result. Environmental influences such as moving the device during the test, individual faulty test kits or, in the case of saliva samples, certain dyes found in food are also conceivable reasons.

If false positive results are suspected, the entire test should be repeated, including taking a new sample and - if possible - using another lot of the test kit. If the result is negative when retested, it is a false positive result. If the result is positive again, the result should be considered positive.

Invalid results

In addition to the actual Covid target genes, the test cards also contain an internal control that tests for a gene sequence present in each sample and is therefore always positive. It tests for the presence of the human housekeeping gene β-Actin.

If the internal control fails to amplify or the signal isn't strong enough, the result will be invalid.

The test card contains several test chambers and a reaction takes place in each chamber. If any of them becomes positive, the entire test will be positive.

By far the most common causes are air bubbles or waiting too long after inserting the card as well as contaminated samples (blood, food, too much nasal secretion..). Possible sources of error also include incorrect storage or expired test kits.

Storage of the test kits

The test kits must be stored in a cool and dry place between 2°-28° C.

Pluslife stated that the test kits remained stable for 52 days in a test at 55 °C, but it is unclear whether this affects the sensitivity of the kits.

We recommend exposing the tests to higher temperatures only for a short time (e.g. during shipping), if at all. Avoid freezing, do not store in a refrigerator.

Frequently asked questions

How long is the test result valid?

We are not aware of any studies that could conclusively answer the question. It is a question of individual risk assessment.

Many experts consider a period of approx. 12 to 24 hours to be safe and appropriate and have had good experiences with it in practice.

A negative Pluslife test is a very strong indication that the person was not infectious at the time of the test. Within the incubation period since the last higher-risk contact, this can of course change and the test must be repeated regularly within the possible incubation period.

The more sensitive a test, the earlier it can detect the virus at the start of the exponential growth phase when viral loads are still very low. This implies a greater "safety buffer" than less sensitive tests: the period during which the virus can already be detected but the person is not yet infectious. While this safety buffer is essentially zero with normal rapid tests, a molecular test such as Pluslife offers a certain degree of safety.

Will throat swabs also work?

Yes. The manufacturer has confirmed that both nasal and throat swabs have been validated. The reason the package insert does not mention throat swabs is due to the accelerated certification process at the beginning of the pandemic and is no longer accurate.

Covid tends to show up in throat samples much earlier than in nasal swabs, which is why many Pluslife users perform a throat swab or combined nasal and throat swab to detect infection as early as possible.

In the recent Imperial College Human Challenge study, almost all patients had detectable virus in their throats 1-2 days earlier than in their noses. Here's an annotated graph from the study. The time delta is marked with red bars:

This suggests that a throat swab or combined nasal and throat swab will have the best results.

We recommend swabbing the throat as well as the cheek and under the tongue. It is important not to eat or drink anything at least 30-60 minutes beforehand to avoid interference. Avoid acidic or alkaline foods.

Are pool tests possible?

Yes, many Pluslife users have had good experiences with small pools (3-4 people maximum). In general, however, the risk of inhibitors and thus an invalid result increases with each additional person. The liquid must also not become too thick, otherwise it can no longer flow through the small capillaries on the test card.

It is worth considering ahead of time how to handle positive pool.

Should let the swab soak in the buffer tube, like with rapid tests?

No, the manufacturer specifically advises against it. After thoroughly "squeezing" the swab, the test should be started immediately (within at most five minutes).

The liquid has already flowed into the chambers before I pushed in the lid.

This is normal and harmless - the pressure exerted on the test card when it is screwed shut is usually enough to force the liquid into the chambers. Nevertheless, always press in the lid, even if it appears unnecessary.

Tiny air bubbles have formed inside the chambers.

Tiny air bubbles are normal and harmless. Large air bubbles can disturb the test procedure - if in doubt, discard the card, use a new test card and be more careful when filling it.

After testing, there are always small bubbles in the chambers, this is also normal.

Liquid level has dropped below the two dashes.

This is normal. The chambers already fill before the lid is pressed in. As long as the liquid level was between the lines directly after filling the card, you're good! Do not add any extra fluid afterwards.

There is no liquid in the chambers.

Looks can be deceiving at a first glance. The chambers can look empty when they are filled entirely.

If there is really no liquid in the chambers, the sample was too thick. Resample and, in the case of a pool, reduce the number of pool participants.

The powder does not dissolve?

The powder only dissolves completely during the test.

The white lyophilized balls are broken before testing?

The breakage of the balls does not affect the test results. As long as the test card is within the validity period, and the appearance of it is not damaged, the ball's shape state will not affect the test.

Can I carry the device with me?

Yes.The manufacturer recommends transporting it in the original packaging to avoid damage from shocks.

The device is a solid-state device. It contains neither moving parts nor any transport safeties.

Nevertheless, the electronics are not indestructible. Strong shocks, vibrations, extreme heat or cold, condensation and similar mischief can damage the optics or the circuit boards. When transporting, pack it well and avoid exposing it to any harsh environments.

For how long will the LED on the device display the result?

The device does not switch off automatically, the result would - in theory - still be readable days later.

However, the test card should be removed as soon as possible after the test, as the heater does not turn off after the test and some liquid will slowly evaporate. This is especially important for positive tests due to the risk of DNA contamination (see above).

Are any components of the kit toxic?

The exact chemical composition of the kit is not known. The manufacturer states that the buffer fluid is corrosive and contact with the skin should be avoided, and although brief contact is harmless, strongly recommends immediately washing off any spillage with water and soap.

We recommend treating the kit like you would treat a strong household cleaner. Use protective gloves and goggles, keep away from children and pets.

Can I use the test cards beyond the expiration date?

The manufacturer recommends not to use expired test cards.

Over time, sensitivity steadily decreases: the activity of the enzymes diminishes and bacteria may grow in the lysis buffer. You can still use test kits that have expired very recently, but do not push it too much.

There is anecdotal evidence that invalid results become more frequent when test cards are used beyond the expiration date, which suggests that some component of the kit does indeed degrade over time.

How can I tell whether my test cards are defective?

If the reaction does not work at all because the enzymes are no longer active enough or the sample contains interfering substances (inhibitors), the internal control would not respond and the instrument would report an invalid test. The internal control therefore guarantees, to a some extent, that the test cards are still OK and will detect high viral loads.

However, it might be possible for the enzymes to degrade - for example, due to incorrect storage - but without failing entirely. In this case, the (highly concentrated) internal control would still work, but sensitivity at very low viral loads would be reduced. We don't know whether this is something that can happen to Pluslife assays. Overall, it is safe to say that kits which aren't expired and were stored appropriately will have preserved their original sensitivity.

Can I operate the device with other power supplies?

If possible, use the power supply supplied with the device which has been verified by the manufacturer to work well with the device. Bad power supplies can cause electromagnetic interference.

Any good USB power supply or powerbank will work just fine as long as they can supply a voltage of 5V and a current of at least 3A/15W.

Powerbanks (for example from Anker) work very well to perform tests on the go without a fixed power supply. However, the device should not be moved during the test.

Laptops, smartphones and similar power sources technically work, but often do not provide sufficient power and should be avoided.

We measured a current of 1.7A at room temperature during the warm-up phase and 0.7A during the test, which is how we calculated the minimum power requirements above. We do not recommend using weaker power supplies since it is unclear to what extent it affects the device's operations.

Where can I get replacement cables?

Unfortunately, Pluslife does not use a normal USB cable, but "USB to weird round plug". Such cables are commercially available, but not too common.

You need the right kind of round plug (5.5 x 2.5 mm; male; outside minus, inside plus, USB to DC 5525):

The following cables are known to work:

Can I use other/additional swabs, for example for pool tests?

Yes, but some materials may interfere with the reaction. The swabs must have good absorption and sample release capabilities and be suitable for PCR reactions.

Cotton, calcium alginate and wrapped (instead of flocked) swabs must not be used. Only use flocked polyester/dacron/rayon/nylon/...

Flocked swabs are best at absorbing and releasing material, which improves the sensitivity of the tests.

The manufacturer currently supplies the kits with FLOQSwab™ flocked nylon swabs. Praxisdienst sells FLOQSwabs with protective tubes, which we find very convenient.

Why is a positive result displayed faster than a negative result?

In a LAMP reaction, DNA is amplified until the strength of the optical signal exceeds a certain threshold, similar to the cycle threshold (Ct) value in PCR.

The higher the viral load, the earlier the exponential growth phase begins.

The device reports the positive result immediately after the threshold was exceeded. However, as there is no such clear indicator for a negative result, the device simply waits and then reports a negative result as long as the internal control has worked and none of the target reactions are positive.

On average, it takes about 10-15 minutes for a positive sample to be reported. Always wait for the entire duration of the test: a weakly positive result can take up to 30 minutes to be reported.

Does Pluslife recognize current variants?

Covid tests generally detect so-called "conserved epitopes", i.e. parts of the virus that do not mutate frequently. Therefore, new variants rarely cause false-negative results. Most recently, this happened with Omicron, which was no longer recognized by some single target antigen tests.

PCR/LAMP usually use multiple targets, so if one of the targets mutates, the other target(s) will still be detected. In the case of Omicron, the so-called "drop out" (i.e. failure of one of the targets) even made it possible to distinguish easily between Omicron and Delta in some assays.

Pluslife targets both N and ORF1ab gene sequences, and is therefore considered robust against mutations. The manufacturer declared on 20/09/2023 that Pluslife recognizes current Omicron variants incl. "Eris".

Can I power the device via its USB-C port?

No, you can only power the device via the round plug. The USB-C port is for data only.

Do I have to turn off the device using a long press on the button, or can I just unplug it?

Unplugging works just fine.

Rapid test positive, but Pluslife negative

If, after a positive rapid antigen test, a follow-up Pluslife test is negative, we recommend repeating both tests several hours apart to exclude stochastic effects and errors. If available, use different lots of each test.

Pluslife is more sensitive and specific than rapid tests and a repeatably negative Pluslife result is therefore more conclusive than a positive rapid test.

We are personally aware of cases in which a symptomatic respiratory infection (of unknown cause) caused false-positive rapid tests in several individuals. In one case, RT-qPCR was performed in addition to Pluslife, which confirmed the negative Pluslife result.

The RKI has confirmed that both rhinoviruses and bacterial pathogens can lead to false positive results. There are isolated case reports in the literature (et al.). The exact frequency and mechanism of action are unknown, but it appears to be relatively common. Since the manufacturers of rapid tests exclude cross-reactions with other respiratory pathogens in vitro in quality assurance, we hypothesize that the mucosal immune response itself is causally involved and might interfere with the response.

In a series of experiments we have ourselves confirmed that many rapid tests are highly sensitive to acids and even small amounts can overcome the acid regulation of the buffer solution, cause nonspecific binding and thus false positive results due to physical effects. Especially in young children with reflux, this possibility should be considered in addition to other interfering substances.

The authors would like to learn more about this phenomenon and we will cover the cost of a respiratory multiplex PCR panel for false-positive rapid tests with negative Pluslife results. Our e-mail address is on the bottom of the page.

How do rapid antigen tests work?

Rapid antigen tests are based on binding the antigens - i.e. viral proteins, not RNA - with special antibody complexes and thus making them visible to the naked eye.

The sample is first stabilized in a lysis buffer, which dissolves the proteins from the virus ("lysis") and raises or lowers the pH of the solution to a certain value ("buffer").

The buffer solution is then dispensed onto the test strip.

Viral antigens first bind to mobile antibodies at the beginning of the test strip, which are marked with a colored marker (usually Colloidal Gold).

These antigen-antibody-gold complexes then bind to another set of antibodies fixed in place on the test line:

This method is prone to false positive results, since antibodies can also bind to each other or to any other proteins under non-optimal conditions such as incorrect pH and other interfering factors. With modern RT-qPCR or LAMP (with probes), this is much less likely: both primer and sample must bind to specific target DNA sequences, which - unlike the protein interaction - cannot easily happen due to purely physical effects.

This also explains the big difference in sensitivity: there must be enough viral protein in the sample to be able to see the resulting complexes with the naked eye.

Rapid tests are therefore only effective when a high viral load is present in the sample. They are of limited use for early detection and prevention of infection.

Change history

Only significant changes are listed.

21.10.2023

20.10.2023

03.10.2023


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