Quantitative results should be reported below the detection limit

detect

To recall:

LoB = limit of blank
LoD = limit of detection
LoQ = limit of quantification

Although there are various ways to calculate these quantities, LoB can be estimated by running some samples without analyte and adding 2 sd to the average. LoD is estimated by running some low samples and adding 2 sd to the LoB. LoQ is estimated by running some low samples and calling LoQ where the data equals a pre specified CV. See here for some pictures.

I’m not sure how most laboratories handle reporting values below the detection limit (LoD) but CLSI EP17-A2 suggests that for values between the LoB and LoQ, the value should be reported as “analyte detected, result < LoQ.”

Some of my blog entries (such as this one) come from my consulting experience, which is of course confidential. So here is a made up example of a tumor marker with a detection limit of 1.0 and some patients who are being serially monitored. As one might expect, no tumor marker is an ideal result.

Patient A: 0.3, 0.6, 0.2, 0.6, 0.3
Patient B: 0.2, 0.5, 0.4 0.6, 0.8

These quantitative results could be compared to the reports for all values of “analyte detected, result < LoQ.”

Clearly, there is something happening with patient B and this trend information is lost by the reporting rules.

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2 Responses to Quantitative results should be reported below the detection limit

  1. sdasd says:

    The lower limit of measuring interval should not
    be confused with detection limit

  2. jkrouwer says:

    If you mean by the lower limit of measuring interval, the LoQ (limit of quantitation, I don’t agree with that concept. Observations with high CVs are still of value.

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