About allowable error

An analyzer profile holds one total allowable error for each analyte. Studies you create from the profile take their limits from it. Sigma uses the full allowance. You can derive the allowance from any of four sources. To enter one, see Set up analyzer profiles.

A profile's allowable error can be a concentration allowance, a percentage, or both. With both, the larger allowance applies. Each-specimen limits in comparison and lot studies copy the total allowance. Bias limits, including comparison bias at decision concentrations, and linearity, interference and stability limits use the systematic allowance. Precision limits use the random allowance. The systematic share starts at 50% and the random share at 25%; you can edit both defaults. Manufacturer claims stay separate from these laboratory limits (About precision).

For example, a glucose profile has total allowable error of 6 mg/dL or 8%, whichever is greater. Its default shares produce an SD allowance of 1.5 mg/dL or 2% of the level mean and a mean-bias allowance of 3 mg/dL or 4% of the assigned value.

A study keeps the allowance and source it copied when it was created. Editing a profile changes newly created studies; existing studies and calculations keep their settings.

Sigma counts how many SDs fit between the bias and the allowable total error at one concentration. Bias and precision limits each get a share of the allowance; sigma uses all of it (Full allowable error). Sigma changes with the chosen TEa. Using repeatability from a single run can overstate sigma (About precision). The study's acceptance limit is the Minimum acceptable sigma you set (Acceptance limits).

Measurement uncertainty combines within-laboratory precision, bias against assigned values and the uncertainty of those assigned values into one expanded uncertainty. The result lists each component (Measurement uncertainty reference). Its inputs are representative within-laboratory precision and results on assigned materials or proficiency events; the data must describe the same measurement procedure, matrix and concentration range. The assigned value's stated uncertainty and coverage factor belong in the calculation; a peer-group SD is a different quantity. An optional expanded-uncertainty limit is the laboratory's own limit, in the calculation unit.

Basis, under Derive the allowance from a published basis, offers four sources. When you use a candidate, its source, the source edition, the inputs and the formula are saved with the profile and copied into every new study. If you edit the allowance directly, it is recorded as a laboratory-selected limit.

• Clinical requirement: the absolute allowance, percentage, or both that your laboratory chooses.
• CLIA proficiency-testing criterion: the numeric PT grading criterion for the analyte, in the profile's unit. The list cites CMS-3355-F, effective 11 July 2024, with the CEA correction, and shows each criterion's restrictions, such as the LDL limit applying to direct LDL measurement and the glucose limit excluding home-use devices.
• Biological variation: worked out from the within-person (CVi) and between-person (CVg) CVs you enter and the performance level you pick: minimum, desirable or optimum. With factor F of 3, 2 or 1 respectively, allowable CV = F × 0.25 × CVi, allowable bias = F × 0.125 × √(CVi² + CVg²), and TEa = 1.65 × allowable CV + allowable bias. For CVi 5.6% and CVg 7.5%, the desirable TEa comes to about 6.96%.
• Achievable from peer precision: worked out from peer mean–SD pairs and your low-control SD. The percentage allowance is the multiplier (3 by default) times the median peer CV, and the absolute floor is the multiplier times the low-control SD, a planning rule based on what peer laboratories achieve. For peer CVs of 2%, 2% and 3% and a low-control SD of 0.5 mg/dL, it gives 6% or 1.5 mg/dL, whichever is greater.