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Reportable Range

Reportable range is the functional range of an assay over which the concentrations of an analyte can be measured with acceptable accuracy and precision. Reportable range should not be confused with reference range. Reportable range includes analytical measurement range (AMR) and clinically reportable range (CRR).

AMR is defined as the range of values an instrument can report directly without dilution or concentration. Accreditation agencies require that AMR be validated at least every six months and after recalibration, changes of reagent lots or major instrument maintenance. Validation can be accomplished using at least three levels of commercial linearity materials, standards or calibrators that span the lower limit, mid-point and upper limit of AMR. AMR validation can also be done by calibration verification (see below).

If material is not available to validate AMRs exact upper limit, it is recommended to use calibrators within 10% to 15% of the ends of the AMR. In this situation, the medical director must write a statement documenting the highest range validated. If patient results are higher than the material used to verify AMR, but less than the stated AMR, they can be reported without dilution. For example, if the AMR is initially determined to be 0 - 1000 ng/dL, but the material available for validation only goes up to 900 ng/dL, patient results between 900 and 1000 ng/dL can be reported. Patient results higher than 1000 ng/dL should be reported with a > sign or diluted before reporting. The medical director must specify and document what the maximum dilutions are for each analyte. Maximum dilutions should be based on medical usefulness.

CRR is the range of values an instrument can report as a quantitative result with dilution or concentration. CRR is typically wider than AMR. Values greater than or less than the CRR are reported as greater than (>) or less than (<). CRR is a clinical decision made by the medical director and does not require periodic revalidation. Dilution or concentration protocols must be documented for each analyte.

The following table demonstrates the relationships of reference range, AMR and CRR for some selected chemistry analytes measured on a Vitros 5600 chemistry analyzer.

Analyte Ref Range AMR Max Dilution CRR
Albumin 3.5-5.0 mg/dL 1.0-6.0 None 1.0-6.0
ALT 13-69 IU/L 6-1000 15 1.0-15,000.0
Bilirubin 0.2-1.3 mg/dL 0.1-22.0 2 0.1-22.0
Cholesterol 100-200 mg/dL 50-325 3 50-975
CK 40-425 IU/L 20-1600 100 Actual result
Creatinine 0.4-1.1 mg/dL 0.1-14.0 2 0.1-28.0
Potassium 3.5-5.3 meq/L 1.0-14.0 None 0.1-14.0

CRR should always be wider than the reference range.

Functional sensitivity (Limit of Quantification) is the lower limit of an analyte that can be reported with acceptable accuracy and precision. Functional sensitivity is important for analytes such as troponin. Several international expert panels including the European Society of Cardiology, the American College of Cardiology, and the American Heart Association have recommended that increased troponin be defined as a value above the 99th percentile concentration of a healthy population as long as total imprecision is <10%.

CLIA 88 requires that reportable range be verified only during method evaluation, but CAP requires that it be verified periodically. This requirement can be met in several ways; by doing a linearity study, performing a correlation study that includes low and high samples spanning the manufacturer’s range, serially diluting a high patient sample, running 20 repetitions of zero standard or a very low patient sample to determine the LLD, and determining acceptable range of recovery for low, medium, and high standards.

 

 

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