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Multiplexed PCR amplifies several targets in one tube instead of one target per tube. It saves reactions, reagent, labor and instrument time, and the published studies show what you pay for that: each primer set usually needs its own tuning, and sensitivity can shift compared with running the same target alone.
Short answer
Multiplexed PCR (also called multiplex PCR) runs two or more primer sets in the same reaction so that several DNA or RNA targets are amplified and read out together. Choose it when throughput and sample economy matter and you can validate the combined reaction against single-target runs. Choose single-target (singleplex) reactions when the last bit of sensitivity matters most.
Definition and scope
A conventional PCR reaction contains one primer pair and amplifies one target. A multiplexed reaction contains several primer pairs, so the same sample yields several amplicons. The read-out has to tell the targets apart, either by amplicon size or by a distinct fluorescent label for each target. The idea applies to endpoint PCR (for example marker genotyping) and to real-time assays such as the qPCR and RT-qPCR workflow. For the basic single-target reaction, see PCR protocol basics.
How it is used in practice
Closed-tube genotyping panels
Hayden and colleagues (BMC Genomics, 2008) described Multiplex-Ready PCR for SSR and SNP genotyping: a single-step, closed-tube reaction run in two stages, with an initial optimisation step for each primer set. A tag primer adds a 30-bp offset to fragment size, and panels were built from markers whose allele sizes do not overlap, in four-plex or six-plex format.
Diagnostic detection with an internal control
Perchetti and colleagues (Journal of Clinical Virology, 2020) combined the CDC N1 and N2 SARS-CoV-2 targets with an extraction control in a single triplex qRT-PCR. The earlier CDC primer/probe sets used the same fluorophore, so each target needed its own run. The triplex put the extraction control into the same reaction as the viral targets. Against the laboratory’s single-plex test it detected 183 of 186 positive or inconclusive samples (98.4%), agreed on all 170 negatives, and showed no amplification of 20 other respiratory infections.
Types: how targets are told apart
| Approach | How targets are separated | Example in the sources |
|---|---|---|
| Size-separated amplicons | Each marker gives a fragment of a different length | Hayden 2008: non-overlapping allele sizes, 30-bp tag offset |
| Separate fluorescent channels | Each target is read in its own detection channel | Perchetti 2020: N1, N2 and extraction control in one triplex |
Where it matters for labs, clinics and supply decisions
Perchetti and colleagues list the gains in lab terms: higher throughput by reducing the number of qRT-PCR reactions run in parallel, lower reagent consumption and labor, and freeing up lab equipment. Those are the figures a lab manager can use when comparing multiplexed and singleplex workflows. Related cost effects on kit and instrument choice are discussed in the GMO testing procurement guide, and the cycler itself is covered in What Is a Thermal Cycler?.
What you give up: a sourced checklist
| Check | What the sources report |
|---|---|
| Per-primer-set tuning | Hayden 2008 tested locus-specific primer concentrations at 20, 30, 40 and 80 nM and found adjustment for individual primer sets necessary. |
| Genome complexity | Hayden 2008: 92% success amplifying published sequences, diminishing with increasing genome size and polyploidy; non-specific fragments appeared in some cases. Tested in apricot, cherry, barley and bread wheat. |
| Sensitivity shift | Perchetti 2020: mean N2 CT of 25.4 in the triplex versus 24.0 in the laboratory-developed single-plex test. |
| Sample input | Perchetti 2020: 11 uL of eluate in the triplex versus 5 uL in the single-plex test. |
| Result rules | Perchetti 2020: positive only if all targets amplified; one N target plus the extraction control only is inconclusive and retested. |
Use the table as a validation plan: compare every multiplexed panel against its single-target reactions before relying on it, and record the comparison as part of assay reporting (see the MIQE checklist). For the single-target alternatives, digital PCR versus qPCR sets out a different trade-off, and melt curve analysis covers reading unexpected peaks in dye-based runs.
Common misunderstandings
“A multiplex reaction performs the same as the singleplex reactions combined”
Not necessarily. In the triplex study the N2 target crossed threshold later than in the single-plex test (CT 25.4 versus 24.0), so equivalence has to be shown, not assumed.
“Any primer sets can be pooled”
The genotyping panels were built from markers with non-overlapping allele sizes, and each primer set still needed concentration adjustment. The early CDC SARS-CoV-2 sets shared one fluorophore and so each target needed a separate run.
“Multiplexing is only for large panels”
Even a triplex, two viral targets plus an extraction control, changed how many reactions the laboratory had to run.
FAQ
What is multiplexed PCR?
PCR in which more than one primer set is present in the same tube, so several targets are amplified and detected together.
What is the difference between multiplex and singleplex PCR?
Singleplex amplifies one target per reaction. Multiplex amplifies several, which reduces the number of reactions, reagent and labor but requires validation against singleplex results.
Can multiplexing lower sensitivity?
It can. One published triplex showed a higher mean CT for a target than the single-plex test (25.4 versus 24.0).
Sources
- Hayden MJ et al. Multiplex-Ready PCR: a new method for multiplexed SSR and SNP genotyping. BMC Genomics 2008;9:80. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2275739 (checked 2026-10-29).
- Perchetti GA et al. Multiplexing primer/probe sets for detection of SARS-CoV-2 by qRT-PCR. J Clin Virol 2020. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7278635 (checked 2026-10-29).
