Page 128 - Clinical Small Animal Internal Medicine

96 Section 2 Endocrine Disease

The presence of elevated plasma fructosamine (approxi-
VetBooks.ir mately >400 μmol/L; reference range varies by labora-
tory) or glycated hemoglobin (A1c) (reference range
depends on assay used) in symptomatic pets with hyper-
glycemia and glucosuria helps confirm the diagnosis of dia-
betes mellitus. However, fructosamine is not consistently
increased above the reference range in cats until blood glu-
cose is approximately >300 mg/dL (>17 mmol/L), making
it unsuitable for differentiating stress hyperglycemia from
diabetes when blood glucose is 300 mg/dL (17 mmol/L) or
less. In contrast, unpublished data suggest the new Baycom
A1c is more sensitive at distinguishing transient hypergly-
cemia secondary to stress from persistent hyperglycemia of
diabetes or prediabetes. Fructosamine is formed when
blood glucose irreversibly binds plasma proteins (mainly
Figure 12.2 Cat with plantigrade stance. Source: Rand 2013. albumin). Fructosamine concentration is roughly propor-
Reproduced with permission of John Wiley & Sons. tional to the average blood glucose concentration over the
preceding 7–14 days, which is the half‐life of albumin in
dogs and cats. Therefore, while a single blood glucose
measurement reflects blood glucose at one moment in
aldose reductase inhibitors three times daily retards time, fructosamine is used as an indicator of blood glucose
progression of ocular changes. over a longer period of time and is used to document per-
sistent hyperglycemia. Similarly, glycated hemoglobin is
formed when blood glucose irreversibly binds hemo-
Diabetic Neuropathy
globin (especially hemoglobin A1), and its concentration
The majority of diabetic dogs, cats, and people have micro- reflects the average blood glucose concentration over
scopic evidence of nerve injury, including demye lination, approximately 70 days (erythrocyte lifespan).
remyelination, and axonal degeneration. However, less A new test (Baycom A1c) validated for cats is available,
than 50% of cats with diabetes mellitus have clinical neu- and may be useful for differentiating cats with blood glu-
ropathy with hindlimb paraparesis, a plantigrade stance, cose in the normal range from those with a persistent mild
and decreased ability to jump, as well as reduced reflexes hyperglycemia, for example prediabetic cats with glucose
and proprioceptive deficits (Figure 12.2). Weakness and concentrations of 130–180 mg/dL (7.2–9.9 mmol/L) or cats
muscle wasting are present in 50% of diabetic cats. Clinical with subclinical diabetes (>180 mg/dL up to the renal thres-
diabetic neuropathy is rarely recognized in dogs. hold of 250–290 mg/dL; >10 mmmo/L to 14–16 mmol/L).
In cats, stress hyperglycemia may be confused with
diabetic hyperglycemia on initial presentation. Stress
Diagnosis of Diabetes Mellitus hyperglycemia is usually (but not always) lower than
diabetic hyperglycemia, with median blood glucose in
Diagnosis of diabetes mellitus is based on demonstration stressed cats around 305 mg/dL (16.9 mmol/L) with a
of persistently increased blood glucose concentration, wide range (126–505 mg/dL; 7–28.1 mmol/L). Median
and is typically associated with glucosuria and classic blood glucose in newly diagnosed diabetic cats is around
clinical signs of polyuria and polydipsia. In dogs, blood 475 mg/dL (26.4 mmol/L) with a wide range of 180–
glucose concentrations above the renal threshold of 1100 mg/dL (10–61. mmol/L) that overlaps with the
200 mg/dL (11 mmol/L) are considered diabetic. In range of stress hyperglycemia. Diabetic hyperglycemia
humans and cats, blood glucose concentrations persis- and glucosuria will be persistent over time, and will
tently above normal but below that considered diabetic always be accompanied by typical clinical signs if blood
(>117 to < 180 mg/dL; >6.5 to <10 mmol/L) are associated glucose is above the renal threshold. In contrast, stress
with increased risk of developing diabetes and considered hyperglycemia typically resolves in 3–4 hours but may
prediabetic in cats. Persistent hyperglycemia of ≥180 mg/ take 24 hours in a very few cats. Therefore, in most cats,
dL (10 mmol/L) should be considered diabetic, but it will an easy way to rule out persistent hyperglycemia of dia-
only be accompanied by clinical signs once it exceeds the betes or prediabetes, is to test a repeat sample from the
renal threshold of 250–290 mg/dL (14–16 mmol/L). Stress ear after the cat has been sitting quietly in a cage for 4
hyperglycemia and postprandial hyperglycemia may hours; in the majority of cats with stress hyperglycemia,
complicate diagnosis of diabetic hyperglycemia in cats. blood glucose will be <117 mg/dL (6.5 mmol/L).