How It Works
Study Design
A PT/INR method comparison collects paired measurements — the same patient sample tested on both the reference method (X) and the test method (Y). Samples should span the full clinically relevant PT range, from normal values through the supratherapeutic anticoagulation range. CLSI EP09C minimum design requirements apply:
| Requirement | Specification |
|---|---|
| Minimum samples | 20–40 patient samples (preferably 100+) |
| PT range | Cover the full clinically relevant range, including normal and elevated values |
| Specimen type | Fresh patient specimens; test as soon as practical after collection |
| Pairing | Same specimen tested on both methods; results matched by Sample ID |
| Reference method (X) | The established or currently used analyzer/reagent system |
| Test method (Y) | The new or candidate analyzer/reagent system being evaluated |
Range matters more than count. A dataset of 40 samples spanning the full PT measurement range (normal through supratherapeutic) provides more meaningful regression results than 100 samples clustered near normal values. Include samples across multiple concentration levels, paying particular attention to the INR 2.0–3.5 range that is clinically most critical for anticoagulation monitoring.