Results with quantitative values + interpretations

gillian · October 20, 2019, 6:25pm

I’m trying to figure out the best way to capture the results of this test:

HIV 1 Quantitative Real Time PCR
HIV 1 RNA, QN PCR: <20, Not Detected, Ref: Not Detected, copies/mL
HIV 1 RNA, QN PCR: <1.30, Not Detected, Ref: Not Detected, log copies/mL
Reportable Range: 20 copies/mL to 10,000,000 copies/mL (1.30 log copies/mL to 7.00 log copies/mL)

70241-5: HIV 1 RNA [#/volume] (viral load) in Plasma by Probe and target amplification method detection limit = 20 copies/mL

could be used for HIV 1 RNA, QN PCR: <20 copies/mL, and I could submit a code for a method detection limit of 1.30 log copies/mL. But when thinking about capturing “Not Detected”, this would have a property of [Interpretation], not [Presence], correct? (even though presence would have a nice structured answered list- are there answer lists for interpretation ever? I haven’t come across any yet.) And for a property of interpretation, how would I differentiate between the (copies/mL) instance vs the (log copies/mL) instance? In a quantitative property it would be part of the property itself. (i.e. [#/volume]).

To summarize, the end goal would be 4 results with corresponding LOINC codes:
HIV 1 RNA [#/vol] detection limit 20 copies/mL = <20 copies/mL
HIV 1 RNA [interpretation of copies/mL] detection limit 20 copies/mL = Not Detected
HIV 1 RNA [log #/vol] detection limit 1.30 log copies/mL = <1.30 log copies/mL
HIV 1 RNA [interpretation of log #/vol] detection limit 1.30 log copies/mL = Not Detected

Am I correct in wanting to use interpretation instead presence for property of “Not detected” results of quantitative labs?
Can answer lists be suggested for interpretations?
Is the best way to indicate detection limit within the code itself?
What is the best way to structure my LOINC code submission to account for interpretation of (#/vol) vs (log #/vol)?

I’m coming across quite a few quantitative+interpretation instances like this, and any ideas/thoughts/guidance would be appreciated. Many thanks in advance!

gillian · October 23, 2019, 1:25pm

Is there a better place/person to ask questions like this?

on9cloud · October 25, 2019, 3:37pm

I am also very interested in LOINC codes for HIV tests. (and would be keen to see answer to your question)

pdbanning · October 27, 2019, 6:49pm

Hello and thank you both for your patience. This is the perfect place to ask such questions!

Gillian had asked about LOINC terms for the following, and I’ve inserted possibilities for your consideration (making presumption on specimen). In the past, Regenstrief has not opted to build at every possible detection limit, but asked users to choose the closest limit. The interpretations have not had a precedence of applying a detection limit in this arena. (you might see how they screen for drugs with cutoff levels in 43983-6 Amphetamines:PrThr:Pt:Urine:Ord:Screen>500 ng/mL)

HIV 1 RNA [#/vol] detection limit 20 copies/mL = <20 copies/mL ---- 70241-5 HIV 1 RNA:Ncnc:Pt:Plas:Qn:Probe.amp.tar detection limit = 20 copies/mL HIV 1 RNA [interpretation of copies/mL] detection limit 20 copies/mL = Not Detected ---- 25835-0 HIV 1 RNA:PrThr:Pt:Ser/Plas:Ord: Probe.amp.tar HIV 1 RNA [log #/vol] detection limit 1.30 log copies/mL = <1.30 log copies/mL ---- 48510-2 HIV 1 RNA:LnCnc:Pt:Ser/Plas:Qn: Probe.amp.tar detection limit = 1.7 log copies/mL HIV 1 RNA [interpretation of log #/vol] detection limit 1.30 log copies/mL = Not Detected ---- 25835-0 HIV 1 RNA:PrThr:Pt:Ser/Plas:Ord: Probe.amp.tar

If you decide to make a submission, use either the RELMA tool or the spreadsheet AND you’ll need to attach package insert of HIV 1 RNA kit and example answers. I would suggest you reach out to the manufacturer for their LOINC codes, as many of them are participating in the HL7 LIVD project.

Let us know what other questions you have,

Pam Banning, Lab LOINC committee co-chair

gillian · October 28, 2019, 12:24pm

Hi Pam,

Thanks for your message. A few follow-up questions:

My understanding for [Presence] is that it is used when the lab performed has a maximum specificity of (for example) Detected/Indeterminate/Not Detected. In these cases, there is a quantitative value for both the copy and log copy version, but the lab is also reporting the result with “Not Detected”. My thinking was that this would be an [Interpretation], rather than [Presence] because we know the specificity is more than detected/non-detected. If this isn’t correct, can you speak more (or point me in the direction of documentation) that explains the difference between Presence and Interpretation properties?

For the suggestions you provided, this would result in both the copy and log copy results having the same LOINC code (25835-0). I’d like to avoid this for accuracy, but I’m not sure what two different codes would look like. I don’t need to include the actual detection limit in the code, but I would like to differentiate “Not Detected” from a copies/mL test vs a log copies/mL test. What would like code look like?

pdbanning · December 2, 2019, 1:38pm

Hi Gillian,

So sorry to slow your work down; I didn’t see this followup question earlier. You’re correct that the answers for a [Presence] term is merely Detected/Indeterminate/Not Detected. It has actually been updated to [Presence/Threshold] to indicate that a cutoff has been applied. An [Interpretation] LOINC actually contains more specific information regarding the patient’s value of the assay.

As for the quantitative difference, copies/mL would go to a [NCNC] numeric concentration LOINC, while log copies/ml would be a [LNCNC] log numeric concentration attribute.

I hope this helps you out.

Pam

system · June 23, 2023, 3:36pm