In a single laboratory, the limit of quantitation, LOQ, equal to ten standard deviations has been recommended.⁴ A test result at this LOQ has an uncertainty of ±30 % at the 99 % confidence level. Similarly here, as a general estimate, the PLOQ, equal to ten repeatability standard deviations is recommended. A test result at this PLOQ has an uncertainty of ±30 % at the 99 % confidence level.

Values below the PLOQ are deemed to be too uncertain for meaningful use in commerce, or in regulatory activities.

Many test methods never find application outside their PLOQ. However, in the quest for ever more sensitive procedures, it can become difficult to distinguish an analytical response from background noise with the technology at hand. Test methods defective in design or poorly executed may also function outside their PLOQ.

1.1 This practice covers the determination of a lower quantitative limit for a test method for an analyte. The determined lower limit is hereinafter referred to as the pooled limit of quantitation.

1.2 Applicable test methods will produce test results greater than zero. Examples are those test methods that measure sample composition.