Tolerance Rule Guidelines
Pass/Fail: Tolerance Rule
A specimen is marked Correct when the analyzer-reported INR and the calculated INR agree within a tolerance of one unit in the last decimal place. This tolerance accounts for rounding that occurs inside the analyzer's internal calculation, which may differ slightly from the externally computed value depending on intermediate precision:
| INR Precision | Tolerance | Example |
|---|---|---|
| 2 decimal places (e.g., 1.25) | ±0.01 | Analyzer reports 1.25 → Correct if Calculated INR is 1.24, 1.25, or 1.26 |
| 3 decimal places (e.g., 1.248) | ±0.001 | Analyzer reports 1.248 → Correct if Calculated INR is 1.247, 1.248, or 1.249 |
The calculated INR is always rounded to the same number of decimal places as the analyzer-reported INR before comparison, using at minimum 2 decimal places.
Worked example
Analyzer reports PT = 13.5 s and INR = 1.25 (2 decimal places). Using ISI = 1.10 and Normal Patient Mean PT = 11.8 s, the module computes:
Calculated INR = (13.5 / 11.8)^1.10 = 1.24
The difference is |1.25 − 1.24| = 0.01. Tolerance at 2 decimal places is 0.01. Since the difference equals the tolerance, this specimen is marked Correct.