Hi,
We have done some more testing on our 92 year old patient whose plasma
glucose levels were between 0.4 and 1.6 mmol/L by hexokinase on the Roche /
Hitachi 917 but normal ( around 5 - 6 ) on a glucometer. Her clinical
symptoms for going to the Emergeny Room supposedly were a drop in blood
pressure ( maybe measured by a nurse ? - she lives in a home ) and back
pain.
We repeated glucose measurements on leftover plasma samples by a glucose
oxidase method ( Beckman LX series) and obtained 5.5 mmol/L, . This
confirms that the patient`s glucose levels are normal but that there is
interference in her plasma when analyzed by hexokinase on our 917. The
reaction monitor on the 917 indicates a very high absorption at 340 nm that
drops paradoxically after addition of R2 , followed by the expected rise as
a result of NADH production, leading to a diminished overall reading for
glucose ( now at 2.0 , higher than originally measured ).
Her total IgM is slightly elevated , with a precipitate at the origin on
electrophoresis ( on a plasma, however ), and we are waiting for a serum to
look for an IgM paraprotein . We suspect that this paraprotein, when
collected in Li heparin, precipitates when mixed with R1 ( Tris buffer at
pH 7.8 ) but redissolves when R2 is added ( HEPES at pH 7.0 ) . The drop in
absorbance then partially hides the rise of absorbance caused by NADH
Thanks to Mailbase and specifically Maria Warner for pointing out this
paper steering us in the right direction
http://www.clinchem.org/cgi/content/full/51/11/2202
***********************************************************
Wolfgang Schneider, PhD, CSPQ, FCACB
Chef du service clinique de biochimie
Hôpital du Sacré-Coeur de Montréal
5400, boul. Gouin Ouest
Montréal, Québec H4J 1C5
Canada
Tél.: (514) 338-2222 x 3171
Courriel: [log in to unmask]
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