How Companion Diagnostics Are Transforming Prescriptions

One change I’ve noticed in recent years is that prescribing is no longer just about choosing a drug — it’s about choosing the right drug for the right patient, backed by a diagnostic test. These are called companion diagnostics, and they’re becoming more common in cancer, infectious diseases, and autoimmune conditions.

For example, before starting certain lung cancer medicines, I now order a genetic test to check if the tumor has an EGFR mutation. If it’s positive, the patient gets a targeted pill instead of standard chemotherapy — often with better survival and fewer side effects.

I also see this trend in infectious diseases. Tests that rapidly detect drug resistance allow me to skip ineffective antibiotics and choose something that actually works. For patients, this means fewer failed treatments and shorter hospital stays.

The pharma industry is pushing this forward by pairing new drug approvals with companion tests. As doctors, it changes how we practice — we’re no longer prescribing blindly, but using molecular data to guide every choice.