Digital PCR vs qPCR: Differences, Pros and When to Use Each
Absolute versus relative quantification – what changes in practice, and how to decide which method your project needs.
Quantitative PCR (qPCR) has been the workhorse of molecular biology for more than two decades. Digital PCR (dPCR) is newer, and in many labs it now sits next to the qPCR instrument rather than replacing it. This guide explains how the two technologies differ, where each one is the better choice, and what to consider before adding digital PCR to your lab.
How qPCR quantifies DNA
qPCR follows amplification in real time. A fluorescent probe or dye reports how much product is present after every cycle, and the cycle at which the signal crosses a threshold – the Ct or Cq value – is compared with a standard curve or a reference gene. The result is relative: it tells you how much more or less target a sample has compared with something else.
That approach is fast and inexpensive, and with 96 or 384 wells per run it scales well. Its weak points are the standard curve itself, sensitivity to PCR inhibitors (which shift Ct values), and limited precision when you need to distinguish small differences such as a 1.2-fold change in copy number.
How digital PCR quantifies DNA
Digital PCR divides each reaction into thousands of tiny partitions before amplification. Some partitions contain at least one target molecule; others contain none. After end-point amplification the instrument simply counts positive and negative partitions and applies Poisson statistics to calculate the absolute number of copies per microlitre.
Partitioning can be done with droplets in oil or in fixed micro-chambers on a chip. In the chip-based CY-PCR-02 digital PCR system, a glass sandwich chip forms more than 20,000 partitions per sample and seals each one by solidifying the oil phase, which prevents droplet fusion and keeps partition size uniform (>99% uniformity, ≥98% effective partitions according to the manufacturer).
Side-by-side comparison
| Digital PCR | qPCR | |
|---|---|---|
| Result type | Absolute copies/µL | Relative (Ct vs standard / reference) |
| Standard curve | Not required | Required for absolute values |
| Rare mutation detection | Down to ~0.01% on capable platforms | Typically ~1% |
| Precision | High, especially for small fold changes | Good for large differences |
| Inhibitor tolerance | Higher – end-point counting | Lower – inhibitors shift Ct |
| Dynamic range | About 5 logs per run | Up to 7–8 logs |
| Throughput | Tens of samples per run | Hundreds of samples per run |
| Cost per sample | Higher | Lower |
| Multiplexing | Up to 63 targets with ultra-multiplex chip dPCR | Usually 4–6 targets |
| Typical uses | Rare variants, CNV, viral load, vector copy number, reference values | Expression screening, routine detection, genotyping |
When digital PCR is the better choice
- Rare mutation and liquid biopsy research. Partitioning separates rare mutant molecules from the wild-type background, so low-frequency variants can be counted rather than inferred.
- Copy number variation. Distinguishing 2 from 3 copies needs precision that qPCR struggles to deliver consistently; dPCR counts both target and reference directly.
- Absolute quantification without standards. Viral or vector copy number, NGS library concentration and reference material value assignment all benefit from a calibration-free result.
- Difficult samples. Because the read-out is end-point, moderate inhibition affects dPCR less than qPCR.
- Highly multiplexed quantification. Ultra-multiplex digital PCR can quantify many more targets than there are colour channels in a single reaction.
When qPCR is still the right tool
For large numbers of samples, quick yes/no screening, gene expression trends with good reference genes, or tight per-sample budgets, qPCR remains the efficient choice. It also offers a wider dynamic range in a single run. Many labs use qPCR to screen and digital PCR to confirm or quantify precisely.
Moving an assay from qPCR to digital PCR
- Start with a well-performing probe assay; check primer and probe specificity.
- Use a master mix designed for digital PCR, or confirm that your system accepts your qPCR mix.
- Dilute samples so that a good fraction of partitions stay negative – too many positives saturate the Poisson calculation.
- Include no-template controls and, where useful, an internal reference assay.
- Set thresholds using positive and negative controls, then verify linearity with a dilution series.
Dedicated digital PCR reagent kits cover probe, dye, one-step RT, ARMS and high-GC chemistries, and chips and consumables are supplied for every run.
Cost considerations
A digital PCR system costs more than a basic qPCR instrument, and consumables cost more per reaction. The comparison changes when one multiplexed dPCR reaction replaces several qPCR reactions, or when calibration standards and repeat runs are removed. Ask for a quotation that includes instrument, chips and reagents for your expected annual sample volume to compare real running costs.
Bottom line
qPCR answers “how much more?” quickly and cheaply. Digital PCR answers “exactly how many?” with high precision and sensitivity. If your work involves rare variants, copy number, absolute standards or multiplexed quantification, adding digital PCR is worth evaluating. See our digital PCR systems overview or read how to choose a digital PCR system.
FAQ
Is digital PCR more sensitive than qPCR?
For rare targets, yes. Partitioning concentrates a rare template into individual partitions, so very low-abundance mutations can be counted. The platform described here specifies 0.01% sensitivity.
Does digital PCR need a standard curve?
No. Digital PCR counts positive partitions and uses Poisson statistics to report absolute copies per microlitre.
Can qPCR assays be moved to digital PCR?
Usually yes. Probe-based qPCR assays often transfer with minor optimisation; chip systems that accept common master mixes make this easier.
Is digital PCR replacing qPCR?
No. The two are complementary: qPCR for fast, low-cost screening; dPCR for absolute values, rare targets and small fold changes.
Which is cheaper per sample?
qPCR is normally cheaper per sample. Digital PCR costs more per reaction but can replace several qPCR reactions when multiplexed.
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