JISCMail - ACB-CLIN-CHEM-GEN Archives

An initial quick way of assessing if an interfering substance might be present in a patient sample is often to do a dilution study and check for linearity. We found out the hard way that a TnT sample should not be diluted. With each dilution step the TnT result increased significantly. Roche (Germany) advised us that they were aware of this and it is due to the dilution disturbing assay equilibrium. I don't know if TnI assays are similarly affected, but assume any equilibrium assay will be to some extent.

From: Clinical biochemistry discussion list <[log in to unmask]> on behalf of Graham Jones <[log in to unmask]>
Sent: Friday, 29 September 2017 7:48 AM
To: [log in to unmask]
Subject: Re: Troponin T /Troponin I discordance

Dear Nicola,

We had a similar case a couple of years ago which was identified as being most likely to be due to a macro troponin T (not previously described as far as I am aware). The key experiment we did was PEG precipitation but we were unable to do a size exclusion chromatography (although the negative result in the lateral flow in the POC TnT may have acted by the same mechanism).

See attached poster,

Graham

From: Clinical biochemistry discussion list <[log in to unmask]> on behalf of Akinlade, Olufunmilayo <[log in to unmask]>
Sent: Friday, 29 September 2017 1:29 AM
To: [log in to unmask]
Subject: Re: Troponin T /Troponin I discordance

Hello all,

We’ve had a patient some time ago from our Rheumatology team. The patient has SLE and polymyositis and a raised Troponin T with no symptoms of chest pain but has an elevated Troponin T

Date

Trop T ng/L

Siemens Trop I (ng/L)

22/12

1694

36.8

29/12

1027

3.4

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5140878/

The Rheumatologists request a Trop I where they feel appropriate.

Regards,

Funmi

From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Coward, Steve
Sent: 28 September 2017 15:40
To: [log in to unmask]
Subject: Re: Troponin T /Troponin I discordance

We produced the following short precision study data (Roche hsTnT assay) on a particular patient, having observed a disproportionate drop in results from serial samples.

Roche concluded, after their own serum fractionation of the sample, that interference was caused by a high molecular weight compound, presumably IgM (and covered by the disclaimer in the method sheet).

Regards,

Steve

Steve Coward

Operational Manager, Automation

Clinical Biochemistry

Belfast Health & Social Care Trust

From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of PULLAN, Nicola (ROYAL UNITED HOSPITALS BATH NHS FOUNDATION TRUST)
Sent: 28 September 2017 14:19
To: [log in to unmask]
Subject: Troponin T /Troponin I discordance

Dear Mailbase,

Any thoughts on this one…

39 yo female, atypical chest pain, Trop Ts ranging from 150-200 ng/L, extensively investigated by cardiology over last 6 months, no cardiac, muscular or autoimmune process identified.

Normal CK

NT-pro-BNP: 84 ng/L (<50)

Trop I: 4 ng/L (<40)

Trop T: 211 ng/L (<14)

Has anyone come across/proved assay interference of this kind in Trop T assays?

Nicola

Nicola Pullan PhD FRCPath
Consultant Clinical Biochemist
Royal United Hospitals Bath NHS Foundation Trust
Combe Park, Bath, BA1 3NG

Dir Line: 01225 824711
Visit our website at: www.ruh.nhs.uk/pathology

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