Legion Diagnostics

Limit of Blank

The Limit of Blank (LoB) is the highest measurement result that can reasonably be expected from a blank sample — a sample containing no analyte. Because all measurement systems produce nonzero readings even when measuring a zero-concentration sample, the LoB defines the upper boundary of that noise. It is a fundamental detection capability parameter that underpins the Limit of Detection (LoD) and the Limit of Quantitation (LoQ).

In practical terms, a patient result below the LoB cannot be distinguished from a blank measurement and should not be interpreted as indicating analyte presence. Understanding the LoB is therefore essential for tests where low-end performance is clinically critical — such as tumor markers, hormones, therapeutic drugs, and infectious disease biomarkers.

Legion Diagnostics supports LoB verification using either the nonparametric or parametric method per CLSI EP17-A2. The module calculates the LoB per reagent lot, reports the maximum LoB across lots as the final result, and optionally compares it against a manufacturer's published LoB claim.

When to Use This Module

LoB verification is required or strongly recommended in the following situations:

  • New method or instrument implementation — Before a measurement procedure enters routine use, the LoB must be verified to confirm that the instrument's noise floor in your laboratory is consistent with the manufacturer's published claim.
  • Analytes with clinically important low-end values — For tests where the medical decision point is near zero — such as troponin, PSA, parathyroid hormone, or drugs of abuse panels — establishing the LoB is essential for correctly interpreting near-zero results.
  • Reagent lot changes — Lot-to-lot variability in reagent composition can shift the blank measurement distribution. Testing with multiple reagent lots ensures that the LoB is stable across manufacturing variation.
  • Verification of manufacturer's claim — Accreditation programs and regulatory requirements may require the laboratory to confirm that the manufacturer's stated LoB is reproducible in the laboratory's specific environment and patient population.
  • Accreditation requirements — CAP and CLIA require documentation of detection capability verification for non-waived quantitative tests, particularly those for which low-end performance is clinically significant.