Acceptance limits

An acceptance limit is a limit your laboratory sets in advance, for example "within-laboratory CV at most 3 %". Each calculation compares the statistic with your limit and gives a criterion outcome.

Where limits are entered#

Limits go on Set up, in Acceptance limits, directly below the study details. Enter the limit before the first calculation: once a study that needs an acceptance limit has data, its main button is Add a limit until one is added. A sigma study has no limits. The 21-position carryover design sets its error limit in its own panel.

Adding your laboratory's limit#

A study with no limits shows two choices: Enter your own limit and, for bias, comparison and linearity studies, Use a CLIA / CAP limit (see CLIA / CAP limits). Once a limit is added, the same two choices sit under Add another limit.

1. Select Enter your own limit.
2. Under What to limit, choose one statistic. Each choice shows its unit.
3. Enter the limit in that unit, for example Largest acceptable within-laboratory CV (%). An allowable difference, such as bias or a specimen difference, has two boxes: one in the study unit and one as a percentage of each level’s or specimen’s own value (see both parts).
4. Choose where it applies (see below). A result exactly on the limit meets it.
5. Select Add limit, then Save changes.

To change a limit, select Edit on it, then Update limit. Remove limit deletes it.

What each study offers#

Study-unit and percentage limits#

For bias, a specimen difference, a deviation from the fitted line or an interference effect, the form shows two boxes, for example Largest acceptable bias (± mg/dL) and Largest acceptable bias (± % of the assigned value). Fill in one or both. The percentage is taken of each level’s or specimen’s own value: its assigned value, comparator or previous-lot result, fitted value, expected concentration or control mean. For Bias at a medical decision level, it is taken of the Medical decision level you enter. With both boxes filled, choose under With both limits: Pass when within either (the larger allowance) or Pass only when within both.

For specimen differences in method, instrument and lot comparison, Pass only when within both keeps a known failure of the study-unit limit when the percentage cannot be evaluated, such as at a zero comparator result. A difference within the study-unit limit stays Undecided until both parts can be evaluated.

Reference interval establishment and LoQ verification have no guided limit. LoQ verification uses the quantitation goal in the detection settings. For a statistic not listed, select More statistics in the dialog.

Levels and direction#

• Applies to is All levels or one level. Before any results exist, it is a text box. Keep * for all levels, or type the level label exactly as it will appear in the data. An SD usually changes with concentration, so add one SD limit per level or use one CV limit for all levels. Instrument comparison offers analyzers and stability offers storage conditions. Method and lot comparison limits cover the whole study.
• A ± limit checks both directions. For a one-sided limit, choose under Direction either Only too high: at most + the limit or Only too low: at least − the limit. A percentage limit applies in both directions.
• Specimen limits in method, instrument and lot comparison are checked at each specimen's concentration. That is its comparative or reference-analyzer result, or its previous-lot result in a lot study.
• For bias at a medical decision level, enter the concentration in the study unit and add one limit per decision level. A decision level outside the measured range can't pass (see no extrapolation).

Type limits with a decimal point (1.5), even if your data use a decimal comma. Enter a ± limit as a positive number.

When no pass or fail is intended#

A descriptive summary or a new reference interval is usually reported without pass or fail. Reference verification can report counts alone, detection verification can report its verification share, linearity can report estimates, and stability can report the tested duration from its allowable-change setting. Their Acceptance limits section reads Optional, and you can calculate without adding one. LoQ verification uses its quantitation goal.

A study that decides pass or fail reads None yet until you add a limit, and its main button stays Add a limit. Method, instrument and lot comparisons need a limit for individual specimens. If they have other limits but none for individual specimens, Set up shows Add a limit for individual specimens before deciding agreement. and Specimen agreement is Undecided, even when mean-bias or regression limits exist.

CLIA / CAP limits#

Bias, method comparison, instrument comparison, reagent lot comparison and linearity studies offer Use a CLIA / CAP limit, taken from the CLIA / CAP proficiency-testing table. The same table is in the menu under Library → Acceptance limits.

1. Select Use a CLIA / CAP limit. When the table has one limit for the study analyte, the choice already shows it, for example Albumin, serum: ±8%, and opens it directly. Otherwise, search by analyte and select Use on its row.
2. The limit dialog opens filled in, with the table row, its source and any note at the top. Choose another analyte goes back to the table.
3. Under What to limit, keep the first choice or pick another, such as Bias at a medical decision level with its Medical decision level. The values stay filled in.
4. Select Add limit, then Save changes. The limit keeps the table as its source unless you change the numbers.

Only a decision-level check asks for a value. Every other supplied limit uses each level’s assigned value, expected concentration or fitted value, or each specimen’s comparator or previous-lot result. Where the table gives an absolute and a percentage part, the larger allowance applies, as the tables state (whichever is greater).

Absolute and combined limits need the listed unit; letter case doesn't matter, so mg/dl matches mg/dL. High-sensitivity CRP, salicylates and testosterone also accept an alternative unit. For any other unit, enter your own limit. Rows based on a peer-group SD, qualitative rules and dilution rules can't be used directly: convert them to a number with your assigned SD or study rule and enter it as your own limit. A table limit is added to any limits already there.

More statistics#

More statistics, under What to limit in the limit dialog, opens the full editor. It offers every statistic the study calculates, including ones the dialog leaves out, such as slope and intercept in method comparison, between-day SD in multi-day precision, or minimum and maximum in a descriptive summary. It appears only where the study calculates more than the dialog lists. For a new reference interval, Enter your own limit opens this editor directly.

Select Add limit, then Save changes. Set up flags a limit for a statistic this study doesn't calculate, such as one copied from another study type. Its outcome is Not applicable.

For Individual specimen agreement, the limit types are Absolute difference limits, Percentage of each comparator result (in lot comparison, Percentage of each previous-lot result), Percentage or absolute, whichever is greater and Concentration-dependent limits; the greater allowance is taken at each specimen’s comparator or previous-lot result. To require a result within both parts instead, use Enter your own limit and choose Pass only when within both.

For glucose at an assigned value of 50 mg/dL, 8% is 4 mg/dL. The greater of 4 and 6 mg/dL is 6 mg/dL, giving a mean acceptance range of 44–56 mg/dL. At 100 mg/dL, the same rule allows 8 mg/dL, giving 92–108 mg/dL. For a decision-level bias check, the limits are centered on zero bias: ±6 or ±8 mg/dL at those concentrations.

Concentration-dependent limits#

Use this for a limit such as ±2 mg/dL up to 100 mg/dL and ±2% above. Available for the Mean or Median in descriptive summary, repeatability and bias studies, the Mean in multi-day precision, Bias at a medical decision level in method comparison, and Individual specimen agreement in method, instrument and lot comparison.

Enter the Assigned value or Medical decision level. A specimen rule needs neither. Then enter one segment per line in Segments · lower, upper, kind, limit:

0,100,absolute,2
100,,relative,2

• A segment includes its lower bound and excludes its upper bound. The last segment also includes its upper bound. An empty upper bound means no maximum.
• kind is absolute (study units) or relative (percent of the assigned value, the decision level or, for a specimen rule, each specimen’s result).
• List segments in order, without overlaps.

The segment that contains the assigned value or decision level sets the limit. If no segment contains it, the limit is not evaluated. In a specimen rule, each specimen’s comparator or previous-lot result picks the segment. A specimen outside every segment has no usable limit.

How the decision is made#

• Decisions use the full-precision statistic, before rounding. A result exactly on a limit meets it.
• Units must match exactly. A unit mismatch gives Undecided.
• A limit for one level is Not applicable to the other levels. If its level matches no level in the data, it is not evaluated and the study can't pass.
• A limit based on fewer than two observations or independent specimens, or on a statistic that couldn't be calculated, is Undecided.
• A specimen with no result or no usable limit leaves a specimen rule Undecided, unless the failures already decide it.

The study status is Criteria met when every limit that applies is met. One unmet limit gives Criteria not met. Otherwise, any undecided or unevaluated limit gives Undecided. The Why panel on Results lists each limit with its outcome. See criterion outcomes.

Changing limits after a calculation#

1. Edit, add or remove limits.
2. Save changes, then Recalculate results. Until you do, the outcomes on screen come from the earlier calculation.

Reusing limits#

• Once a study has limits, Save as a reusable set, beside Add another limit, saves them under a name, with this study's analyte, unit, matrix and instrument. Saving again under the same name makes a new version.
• A study with no limits shows Reuse limits from a saved set or another study when there is something to reuse: a saved set for the same analyte and unit, or another study of the same type and unit in this project. Pick it under Copy the limits of and select Copy limits, then Save changes.

Check the copied limits before you calculate. In the menu, Library → Acceptance limits lists your saved sets, with Rename and Delete (a deletion is permanent and asks first), and the CLIA / CAP table.