Hannah Mamuszka and Lena Chaihorsky make the case that diagnostics — not just drugs — are the key to controlling healthcare spending, and that the U.S. systematically underuses them. They lay the groundwork for the series: primary diagnosis (what's actually causing your symptoms), the "diagnosis of exclusion" trap, and two kinds of tests that determine whether a prescribed drug will work for you — pharmacogenomic tests (how your genes affect drug metabolism) and response-predicting diagnostics (whether you'll respond at all). The recurring villain is economics: insurers balk at a $200 test to protect a $10 prescription, ignoring the clinical and downstream costs; physicians skip testing to spare patients surprise bills; and because most drugs work in only a minority of patients, the resulting churn is profitable. They argue this is why response-predicting tests in areas like rheumatoid arthritis exist but aren't covered — using them would upend rebate-driven formularies. The through-line: we'll pay almost anything for a drug, but won't pay to find out if it will work. Their closing prompt for listeners: ask your doctor how they know this drug is right for you.

Key takeaways

• Diagnostics are the "GPS" of care: without an accurate diagnosis and the right tests, treatment becomes expensive trial-and-error — yet the U.S. spends a small fraction on diagnostics relative to drugs.
• Two kinds of tests can tell you whether a drug will work before you take it: pharmacogenomic tests (how your body metabolizes a drug) and response-predicting tests (whether you'll respond at all).
• The economics are backwards: a cheap test that prevents a wrong prescription is often refused because the savings and harms are downstream, while the churn of failed prescriptions is profitable.
• The patient's question — for any new prescription — should be: "How do you know this drug is right for me, and is there a test that would tell us?"

Relevant links

• Check to see if your drug has a pharmacogenomic test associated with prescription: https://www.clinpgx.org/
• Diagnostic errors in the U.S. — overall error rate and harms (NIH/National Academies review): https://www.ncbi.nlm.nih.gov/books/NBK588113/
• How effective are common medications — realistic drug-efficacy meta-analyses (BMC Medicine): https://link.springer.com/article/10.1186/s12916-015-0494-1
• Genetic determinants of warfarin dose (VKORC1, CYP2C9) — PLOS Genetics: https://journals.plos.org/plosgenetics/article?id=10.1371%2Fjournal.pgen.1000433
• Inadequate response to first-line anti-TNF therapy in RA (~30–40%): https://journals.sagepub.com/doi/10.1177/1759720X221114101
• FDA approval standards and the absence of comparative-effectiveness requirements (NEJM): https://www.nejm.org/doi/full/10.1056/NEJMp0906490