LOB versus LOD versus LOQ
Calibrator A is a blank or “zero” specimen – it contains no AMH. If Calibrator A is re-tested many times there will be as many results above the average absorbance as below, so it would not be surprising (i.e., it is not necessarily a discrepancy) if a patient specimen with undetectable AMH gave a single testing absorbance lower than Calibrator A – simply statistical variance.
The LOD (limit of detection) is the smallest concentration of AMH that can be measured with 95% confidence. It is the AMH concentration that gives an absorbance greater than the upper 95% confidence limit of repeated Calibrator A absorbance values. In other words, the LOD is the lowest amount of AMH that can be detected; but the imprecision of repeated measurements is very high.
The LOQ (limit of quantitation) is the smallest concentration of AMH that can be measured with less than 20% coefficient of variation – in other words this concentration and above can be reported as a value with confidence (repeated testing will <20% CV).
How results are reported is a lab director decision and depends on the clinical use of the test as well. For AMH most labs would report values below the LOQ in ng/mL as < the LOQ.
For laboratories reporting complete information for an analyte where the use requires it – here is an example from the Clinical Laboratory Standards Institution publication entitled “Evaluation of Detection Capacity for Clinical laboratory Measurement Procedures; Approved Guideline- Second Edition.” CLSI Documents EP17-A2, 2012.
For an assay with LOB = 6 mmoL, LOD = 8 mmoL, and LOQ = 10 mmoL
|If the result is:||Report as:|
|5 mmoL||Substance not detected; result <8 mmoL|
|9 mmoL||Substance present, cannot be quantified; result < 10 mmoL|
|11 mmoL||Result = 11 mmoL|