*Add unit for log10 variants of "EID 50", [TCID_50] and [CCID_50]

[timbrisc]

Issue migrated from trac ticket # 129

component: help | priority: minor | keywords: EID 50 log10 CDISC [TCID_50] [CCID_50]

2012-03-16 16:56:31: [email protected] created the issue

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Note: "EID 50" is proposed in separate ticket: http://www.unitsofmeasure.org/ticket/128

CDISC defines the following codes: C70479 "Log10 50 Percent Embryo Infective Dose" (log10 EID 50) definition: A potency unit for measuring infectious activity of a biologic product or infectious agent equal to a base-10 logarithm of amount of product or agent preparation that causes infection in the 50% of embryos (such as chicken embryos) used in the product potency assay or pathogen activity assay.(NCI)

C70480 "Log10 50 Percent Embryo Infective Dose per Dose" (log10 EID 50/dose) definition: A logarithmic-scale (base 10) potency unit for measuring infectious activity of a biologic product or infectious agent preparation equal to the potency at which one dose of infectious material contains one 50 percent embryo infective dose.(NCI)

C70485 "Log10 50 Percent Cell Culture Infective Dose" (log10 CCID 50) definition: A potency unit for measuring infectious activity of a biologic product or infectious agent preparation equal to a base-10 logarithm of amount of product or agent preparation that causes infection in the 50% of the cell culture-containing vessels inoculated with that dilution of infectious material in the product potency assay or pathogen activity assay.(NCI)

C70485 "Log10 50 Percent Cell Culture Infective Dose per Dose" (log10 CCID 50/dose) definition: A logarithmic-scale (base 10) potency unit for measuring infectious activity of a biologic product or infectious agent preparation equal to the potency at which one dose of infectious material contains one 50 percent cell culture infective dose.(NCI)

C70488 "Log10 50 Percent Tissue Culture Infective Dose" (log10 TCID 50) definition: A potency unit for measuring infectious activity of a biologic product or infectious agent preparation equal to a base-10 logarithm of amount of product or agent preparation that causes infection in the 50% of the tissue culture-containing flasks inoculated with that dilution of infectious material in the product potency assay or pathogen activity assay.(NCI)

C70489 "Log10 50 Percent Tissue Culture Infective Dose per Dose" (log10 TCID 50/dose) definition: A logarithmic-scale (base 10) potency unit for measuring infectious activity of a biologic product or infectious agent preparation equal to the potency at which one dose of infectious material contains one 50 percent tissue culture infective dose.(NCI)

The "per dose" ones obviously aren't appropriate as UCUM concepts, but support the need for the base concept.

Prevalence of these codes, based on google searches, is as follows:

"log10 EID 50" 428 "log10 EID50" 2600 "log EID 50" 1860 "log EID50" 3700

"log10 CCID 50" 1080 "log10 CCID50" 1900 "log CCID 50" 634 "log CCID50" 607

"log10 TCID 50" 1380 "log10 TCID50" 4370 "log TCID 50" 8560 "log TCID50" 5740

-Discussion:* These three are being proposed together because they all deal with essentially the same concept differing only by the experimental mechanism used to evaluate the effective dose. Therefore it's reasonable to presume that if one were accepted, all would be accepted or vice versa.

Gunther's comments: Logs are a concern. The logs change the kind of property, they are not just a unit. Should we not expect that when a potency is reported using unit X and potency of a volume V is 1 X, then twice the volume of the substance should have potency 2 X. Once you introduce logs this stops being true. This is not just an issue of units.

Lloyd's response: I agree logs are an issue in terms of combining units together and I have no background in the specific use of these units. However given its prominence of usage on Google, it seems that the log10 variant is clinically significant. I expect this is because potency varies across a wide range and order of magnitude is a better measure of potency. As well, the "log" versions of the codes were actually all registered in CDISC prior to the non-log variants, also leading weight to the relevance of the log variant.

UCUM has other logarithmic units and presumably these are referenced as often as they are because expressing the value in logarithmic form has scientific significance. If data is captured and shared as a log, UCUM should support it. The logarithmic nature of these codes is clearly exposed, flagging that the mathematical operations that can be performed on quantities with these units vary. (In practice, adding these potencies together would have very questionable usefulness.)