Why Printer Paper Is a Bad Choice For PCR Testing

PCR testing is a complex process that relies on a precise balance of chemical reactions and controlled temperature changes. In this article, we aim to simplify key aspects of the PCR workflow to explain why common consumer papers—such as printer paper, copier paper, and notebook paper—are unreliable and inappropriate substrates for PCR testing.

Use of Consumer Paper in PCR Testing

First and foremost, standard laboratory protocols do not permit the use of consumer writing or printing paper in PCR testing.

Paper is manufactured from a wide variety of materials, including cotton, linen, and wood pulp, often in blended formulations. Each of these materials can interact differently with the chemicals used during DNA extraction and PCR amplification. Some may be relatively inert, while others can actively interfere with the reaction.

In addition, paper manufacturing involves numerous chemical treatments and finishing processes. These chemicals—many of which are not disclosed or easily identifiable—can remain as residues within the paper and subsequently enter the PCR reaction.

How Paper Interferes With PCR

When we say that paper can “interfere” with PCR, we mean that it can:

• Completely inhibit the reaction during the lysis or amplification stages, or

• Produce inaccurate results, such as false positives or false negatives (most commonly false male results in avian gender testing).

Even when blood or tissue is scraped from paper prior to extraction, microscopic fragments of the paper and its chemical residues can remain in the sample. Because PCR operates at the molecular level, even trace contaminants can disrupt the reaction.

Lysis and DNA Extraction

The first step of PCR testing is lysis. A chemical lysis solution is used to suspend the sample, which is then heated for a defined period. This combination of heat and chemicals breaks open cells, releasing genetic material into the solution (the lysate).

This process cannot be visually confirmed. Whether lysis and extraction were successful is only determined after PCR is completed.

Once lysis is finished, the lysate must be neutralized using a buffer solution. At this stage, two critical conditions must be met:

1. DNA extraction must have been successful, and

2. The lysate must fall within a specific pH range.

If the pH is too high or too low, the PCR reaction will fail. This is one of the primary points at which chemical contamination from paper can block or destroy the reaction. Unfortunately, there is no reliable way to selectively remove these contaminants without significantly increasing testing costs.

PCR Amplification

Next, an extremely small volume of lysate—typically 1 microliter (µL)—is added to a PCR master mix. For reference, 1 µL is approximately the size of a small freckle. This minuscule volume must contain sufficient intact DNA for amplification to occur.

If inhibitory substances are present in that 1 µL, the entire PCR reaction can fail.

The PCR mixture is then subjected to repeated cycles of heating and cooling. During these cycles, target DNA sequences are amplified and bound by primers that identify the specific genetic markers being tested.

Visualization by Electrophoresis

After PCR is complete, the results are still not immediately visible. Visualization occurs during gel electrophoresis, where the amplified DNA is loaded into an agarose gel and exposed to an electrical current. This causes DNA fragments to migrate through the gel and form visible bands.

For avian gender testing:

• One band at the correct location indicates a male result

• Two bands at the correct locations indicate a female result

• No bands indicate either absence of DNA or chemical inhibition preventing visualization

In cases involving paper submissions, the most common cause of “no band” results is chemical inhibition originating from the paper itself.

Our Laboratory Policy

When we receive samples submitted on standard paper, we immediately inform customers of the associated risks. Some customers note that other laboratories accept paper-based submissions without issue.

Our policy is grounded in providing reliable science at an affordable price. To maintain reliability, we must minimize variables that can compromise results. For this reason, we strongly discourage sample submissions on standard consumer paper.

Can such samples sometimes work? Yes.

Are they reliable? No.

Just because a method can work does not mean it should be used—especially when clients depend on us for accurate and trustworthy results.

We acknowledge that some laboratories allow submissions on printer or notebook paper, and that accurate results may occasionally be obtained this way. However, this practice does not align with accepted scientific standards and is not conducive to maintaining consistent accuracy or affordable pricing.

Acceptable Paper Substrates

The only consumer-accessible paper we readily accept is filter paper (such as coffee filters). For those with access, Whatman blood spot cards and comparable products remain the industry standard.

We will provide Amazon links to approved paper products that can be safely used instead of standard printer or notebook paper.

Dried Blood Spot/ Specimen Paper: https://a.co/d/7YALwB0 Dried Blood Spot/Specimen Paper (non-Amazon): CLICK HERE Whatman Filter Paper: https://a.co/d/dQcaLJR Espresso sized filter papers: https://a.co/d/bK67N1r Standard coffee filters: https://a.co/d/diEjzGT