Page 370 - The Veterinary Laboratory and Field Manual 3rd Edition

Clinical chemistry 339

or primary endocrine disorders) but a mild of nerve and muscle tissues. Levels of calcium
rise can be seen in ‘physiological stress’ and a depend to some extent on the relative ratio of
range of metabolic disorders. Low blood glu- calcium and phosphorus in the diet and also on
cose (hypoglycaemia) may result in collapse and the correct function of the parathyroid glands,
coma and can be associated with a range of dis- gut and kidneys which regulate the levels of
orders. Marked hypoglycaemia may occur after Ca/P. Disorders such as hypocalcaemia (low
administration of insulin in diabetic animals and blood calcium) are often the result of rapid cal-
moderate hypoglycaemia occurs in starvation cium demand associated with late gestation or
and some other endocrine or neoplastic disor- early lactation. If the parathyroid gland is unable
ders. Metabolic diseases such as ‘twin lamb’ to produce parathyroid hormone to promote
disease and bovine ketosis occur when the diet release of calcium from the bones and enhance
is inadequate in calories or too low in glycogenic uptake from the kidney and across the intesti-
precursors (that is, propionic acid) with resul- nal tract, the animal’s calcium levels fall with
tant depletion of liver glycogen stores and low resultant staggering and ultimate collapse. The
blood glucose. The level of ketones (‘ketone bod- latter is common in high yielding dairy cows
ies’) is elevated in most cases of hypoglycaemia and can be prevented by provision of adequate
and these may be detected in the urine. Diabetic calcium supplements, vitamin D in late gesta-
animals may develop ketosis due to inability to tion and early lactation and not too much during
use the glucose in the blood. early gestation (this would make the parathyroid
gland unresponsive later in pregnancy). Calcium
imbalance may also occur in renal disease or
Electrolytes when the diet is too high in phosphorus with
resultant changes in bone density and second-
Electrolyte levels may be measured to determine ary bone damage; this is more common in dogs
the nature and degree of metabolic disturbances and cats. Low levels of magnesium (hypomag-
especially in monogastric species following vom- nesaemia) occur when livestock graze pasture
iting (depleted Cl– and H+ leading to alkalosis), low in magnesium; this can result in staggering
diarrhoea (depleted K+ and HCO– leading to and behavioural changes. Levels of magnesium
acidosis) or blood loss. Dehydrated animals may are also low in ruminants during early lactation
require fluid therapy and this must be selected so the appropriate treatment for animals that
according to the specific needs of the animal. ‘go down’ during lactation may depend on the
Imbalance of sodium and potassium may occur extent of hypocalcaemia and/or hypomagnesae-
in some endocrine disorders, drug therapy for mia. Laboratory tests can help animal health
heart disease, and in renal disease. professionals in making decisions about treat-
The correct balance of electrolytes in the ment options although in many cases treatment
blood is usually maintained by the respiratory may need to be initiated before test results are
and renal system and is important for the main- available.
tenance of fluid balance.

Plasma pepsinogen
Minerals
Pepsinogen is an enzyme released when the
Normal serum calcium and magnesium levels abomasal mucosa is damaged during helminth
must be maintained to ensure correct function infestation, especially Ostertagia sp. in cattle (see

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