I had a poster on this in Focus 2004
Greiner and BD serum gel tubes both showed false positives using the Beckman Access. Sarstedt tubes had no false positives, Greiber were much worse than BD.
Centrifuging serum just before analysis helps however I recommend heparin plasma. I have seen no false positives in 9 years apart from one sample which had chylomicrons.
Mike Collins
BMS3
Biochemistry Automation
Norfolk & Norwich University Hospital
England
From: Clinical
biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of
Steven John Mccann
Sent: 13 November 2013 16:00
To: [log in to unmask]
Subject: Siemens troponin I ultra assay serum v plasma and ?flyers
Hi there,
Currently we use serum (greiner tubes) for routine work however it appears that around 1 in 300 of our positive TnI results on repeating on the same specimen come back negative. We use a cut-off of 20ng/L and currently repeat all samples
above this to confirm the result. Negatives go straight out. The change noticed is beyond the 20ish% CV of the assay such that on some occasions results have been > 100ng/L but on repeat are <20ng/L. The samples are not spun prior to repeat testing. The cause
is proposed to be microclots which affect us due to our rapid analysis.
Do other users delay analysis to allow for complete clotting or use plasma instead? Do any other labs repeat positive TnI on the same sample if serum or plasma is used to check for ‘flyers’?
Thank you for any replies.
Steven
Steven McCann FRCPath EurClinChem
Consultant Clinical Biochemist and Clinical Biochemistry Lead
Stepping Hill Hospital
Poplar Grove
Stockport NHS Foundation Trust
SK2 7JE
Tel No 0161 419 5619
Fax No 0161 419 5668
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