How to get the most out of endocrinology samples

How to get the most out of endocrinology samples
General consideration:
Reason for taking the sample can be
- confirming the clinical diagnosis (try to
take serum samples to avoid influence
from hemolysis, try to have fastened
animals, call the animal in separately to
avoid excess waiting time if possible)
- control of therapy (prior to test check for
best time post pill to get a valuable interpretation).
Hyperthyroidism in cats
Parameter of choice is serum T4. Serum
concentrations change throughout the day,
in early onset of disease you may get results in the upper normal range. An additional freeT4 may give you elevated concentrations in these cases. A recheck after
approximately 4 weeks is usually recommended if suspect clinical diagnosis is not
confirmed and other diseases are ruled out.
The diseases occurs age correlated, normally no one seen under age of 2, up to
30% positive animals in our clientel in the
age group of 10 and above.
Not only in dogs but in cats as well we can
see the sick euthyroid syndrome: lowered
T4 concentrations due to general disease.
Check the animals under medication
within one week, since some may respond
fast and go into hypothyroidism.
Hypothyroidsm in dogs
Parameter of choice for start up of diagnosing is combined evaluation of T4 and
TSH in serum.
Only 6% of our clientel show clear signs
for hypothyroidism (elevated TSH and
lowered T4), whereas 40% come out as
clear euthyroid.
A vast group of animals show lowers T4
and not influenced TSH, being interpreted
as either sick euthyroid or hypothyroid
with lack of response in the pituitary gland
(= lack of responding elevated TSH due to
the lowered T4). A response to lots of diseases by lowering the metabolism and lowering the T4 levels is a physiologic reaction leave us with a diagnostic dilemma
concerning the hypothyroidism for long.
Since this happens in roughly every 2nd
patient and cannot be influenced by more
advanced diagnostic procedure- explain the
possibility of this outcome to the client
beforehand! Further diagnostic approach
is: retest in 4 weeks time or continue with
TSH stimulation test (more expensive but
best way to distinguish) or TRH stimulation test (less expensive, slightly more
animals staying in the grey zone of interpretation).
Hyperadrenocorticism
Never start with single parameters – always chose function tests right from the
beginning! Reasons are:
1. Any stress may produce elevated Cortisol levels that are hard to interpret.
2. Due to changing concentrations of hormones during the day only 20% of the
animals clearly positive for hyperadrenocorticism show elevated cortisol
concentrations in the resting sample.
3. ACTH need more preanalytic precautions and does not differentiate clearly in
many cases.
Test of choice is low dose dexamethasone
test with best sensitivity (=ability to identify a diseased animal) and very reliable
specificity (=ability to identify a healthy
animal). ACTH stimulation test has a some
what lower sensitivity combined with a
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higher specificity and – most important
draw back to me - a higher number of
questionable results. In our experience we
have 15% questionable results in low dose
dexamethasone tests and in contrast 26%
in ACTH tests.
Both tests mark 32% of the animals tested
for Cushing as clearly positive. When the
low dose dexamethasone test is run, sampling three times (time zero, 4 hours post
injection and 8 hours post injection) should
be favoured. This way the additional information on the type of hyperadrenocorticism can be diagnosed as well (= pituitary
or adrenal).
ACTH stimulation test is reserved for all
cases with suspect iatrogenic cause and for
therapy control.
When sampling, don’t forget to mark the
different samples with numbers (e.g. sample 1,2,3 or 8 o’clock, 12:00, 16:00) to
give the lab the chance to perform plausibility control and to prevent content from
different tubes from being mixed.
Therapy control is performed with ACTH
stimulation test, both for the beginning of
the therapy as well as long term monitoring (optimum interval is 1,3,6,12,24,48
weeks after onset of treatment). In case of
scarce money available rather reduce to
one sample (this being the post stimulation
sample) than skip the control totally.
Diabetes
Since serum glucose levels are strongly
influenced by stress ( in cats even more so
than in dogs) we favour the screen of fructosamins in serum, this being a marker for
a long lasting elevation of serum glucose.
Elevated levels should off course be confirmed (e.g. repeated samples, urine and
serum glucose).
Therapy control short term has to be performed by serum glucose, while the long
term control can be carried out using fructosamine levels again. The advantage of
fructosamines in long term control are:
1. Represents an integral of glucose concentration over some weeks time
2. Sampling time is not dependent on the
time of medication or feeding.
Insulinomas
In suspect insulinomas combined measurement of insulin and glucose is best
choice. Glucose is metabolized by any
metabolic active cell in the fluid. Insulin is
degraded by erythrocyte bound enzymes. It
is therefore crucial that you centrifuge the
sample after clotting and be sure to gain a
cell free supernatant as serum (in case of
doubt rather send a smaller amount, repeat
the centrifugation procedure or else). The
cell free serum can then be transported as
usual and time and temperature are not
crucial.
Hypoadrenocorticism (M. Addison)
While first tests with suspect hypoadrenocorticism are non hormonal (e.g. Na, K
with Na/K ratio > 27), the hormonal test of
choice for confirmation is ACTH stimulation test. In our clientel roughly 10% of
the ACTH tests show a pattern resembling
either iatrogenic hyperadrenocorticism or
hypoadrenocorticism (M.Addison).
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Prinzregentenstr.3 • 97688 Bad Kissingen • Telefon: 0971/72020 • Fax: +49/971/68546 • www.laboklin.com