PCR vs Sequencing: Choosing Molecular Diagnostics for a Clinical Microbiology Lab

Every clinical microbiology laboratory investing in molecular diagnostics eventually faces the same question: how much budget should go to PCR-based platforms, and how much to sequencing? The two are often discussed as competitors, but they answer different questions. Choosing well means matching the technology to the job it needs to do, rather than buying the most impressive instrument in the room.

What PCR does best

PCR — and the multiplex and syndromic panels built on it — is fast, targeted, and relatively cheap per test. It answers a specific question: is this organism or resistance gene present? For suspected meningitis, sepsis, or respiratory infection, a syndromic panel can return an actionable result in an hour or two, which is what changes management. Its limitation is the flip side of its strength: PCR only finds what it is designed to find.

What sequencing adds

Sequencing is open-ended. Instead of "is X present?", it asks "what is here, and what is its full genetic profile?" That makes it the right tool for characterising a complete resistance genotype, identifying pathogens that panels miss, and — critically for AMR — determining whether isolates are genetically related. That last capability is what turns a cluster of resistant infections into a confirmed outbreak with a traceable transmission chain. The trade-offs are cost, turnaround, and the bioinformatics expertise needed to interpret the data.

How to decide

Frame the choice by purpose rather than platform:

• Rapid diagnosis of the individual patient — PCR and syndromic panels, where speed drives decisions.
• Full resistance characterisation and unusual mechanisms — sequencing, often as a reference or reflex test.
• Outbreak investigation and genomic surveillance — sequencing, because relatedness cannot be inferred from a PCR result.
• Screening known high-priority genes at volume — PCR, for cost and speed.

Most laboratories need both, tiered sensibly: PCR at the front line for speed, sequencing behind it for depth, outbreak work, and surveillance. The mistake is buying a sequencer for prestige while routine rapid testing is still unreliable.

Build the foundation first

Whatever the mix, molecular diagnostics sit on top of a functioning laboratory: quality systems, external quality assurance, competent staff, and — for sequencing especially — the bioinformatics capacity to turn raw reads into meaning. Decide what questions you most need to answer, build the capacity to answer them, and let that drive the purchase — not the other way around.

Technology choices should be made against each laboratory's case mix, budget, and existing capacity.