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Why
should samples not be collected in serum gel tubes?
It
is suspected that serum gel tube samples may give falsely low
readings as some of the phenobarbital may be absorbed into the
gel. Current advice is to avoid this type of submission tube. |
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Can
a phenobarbital assay be run on a haemolysed sample?
Ideally
all samples submitted should show no signs of haemolysis, however
mildly haemolysed samples may be acceptable. |
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When
is the best time in the dose cycle to take a sample?
The
most useful single sample is the trough phenobarbital concentration,
i.e. immediately before a dose is due. If it is not practical
to collect a sample at this time then try to take subsequent
samples at the same time in the dosing cycle. Some authors advocate
the use of peak phenobarbital levels as well (2 to 4 hours post-pill)
to check the maximal serum concentration. A recent article (Levitski
RE & Trepanier LA, 2000) suggested that in most cases this
is not necessary. |
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I
often get lipaemic samples from epileptic dogs – is
it OK to submit these?
Yes
this is a common finding. Lipaemic samples usually don’t
present a problem. They may need to stand for 24 hours after
arrival at the laboratory to settle out before they can be tested.
Hence there may be a delay in receiving the result. |
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What
can I do if I need advice on the results?
Please
contact one of the veterinary advisors at Vetoquinol, who will
be very happy to try to help. Have all the case details to hand
when you call to facilitate case discussion. |
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What
is the normal therapeutic range for serum
phenobarbital concentrations?
Different
laboratories and books quote reference ranges using a variety
of reference units. You should always be careful to check the
reference ranges for each individual laboratory. The references
ranges for therapeutic serum phenobarbital concentrations in
the two common units in use are:
micromol/l
(typical reference range 65-194 micromol/l).
microgram/ml (typical reference range 15-45 microgram/ml). |
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What
is the purpose of the questions about drug dosage, degree
of control of seizures etc on the submission form?
There
are two reasons to provide this information. Firstly we collate
the results from all the samples submitted with completed forms
and have created a database of this information. We are now investigating
the correlation between various parameters - for example the
percentage of cases controlled at a certain serum phenobarbital
level. Secondly, should you want advice on a specific result
this baseline information might be needed to discuss the case. |
