Page 153 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Calcium: Hypercalcemia and Hypocalcemia 143

Hypoadrenocorticism the serum tCa measurement incorrectly assessed iCa sta-
Hypoadrenocorticism is the second most common cause of tus in 36% of dogs and 32% of cats. 518,519 The use of the
“adjusted tCa” value incorrectly assessed iCa status in
hypercalcemia in dogs (after malignancy), accounting for
11% to 45% of cases in five studies, 115,166,314,586,614 but approximately 53% of dogs with CRF. In dogs, serum
no cases were reported in one study. 46 Hypercalcemia was tCa measurement or adjusted tCa measurement
overestimated hypercalcemia and underestimated hypo-
reported in 28% to 31% of dogs with glucocorticoid- and
mineralocorticoid-deficient hypoadrenocorticism, 442,445 calcemia. In cats with CRF, serum tCa measurement
overestimated normocalcemia and underestimated
in some dogs with glucocorticoid-deficient hypoadreno-
corticism, 328 and in 1 of 10 cats. 443 In a study of 36 dogs hypercalcemia. Thus, to accurately assess calcium status
in patients with CRF, iCa concentration must be directly
with hypoadrenocorticism, 42% had an increase in tCa,
3
but only 22% had increases in both iCa and tCa. The ion- measured.
Fewer than 10% of all dogs with CRF have increased
ized hypercalcemia was typically mild, but a few dogs
serum iCa concentrations. In one study, approximately
exhibited moderate to severe hypercalcemia. In eight dogs 118
6% exhibited ionized hypercalcemia. In a recent study
with hypoadrenocorticism, tCa was elevated in all eight,
of 490 dogs with CRF, 9% exhibited hypercalcemia, 55%
but iCa was elevated in only five of seven dogs in which
221 were normocalcemic, and 36% were hypocalcemic based
iCa was measured. PTH was within or below the refer- 519
ence range in all dogs, 25-hydroxyvitamin D was within on serum iCa concentrations. In another recent study
or below the reference range in all dogs, and calcitriol was of dogs with hypercalcemia, 17% were diagnosed with
withinthereferencerangeinsevenofeightdogs.Hypoadre- renal failure and were hypercalcemic based on their iCa
375
nocorticismisrarelyrecognizedincats,andhypercalcemiais concentration. Of these dogs, 89% had chronic renal
present in only 8% of cases. 35 Hypercalcemia was present in failure and 11% had acute renal failure. Cats with CRF
onecatwithiatrogenicsecondaryhypoadrenocorticismand appear to have a higher incidence of ionized hypercalce-
diabetes mellitus. 541 Magnitude of hypercalcemia was mia as compared with dogs. In 102 cats with CRF, 29%
greatest in the most severely affected dogs, but the mecha- were hypercalcemic, 61% were normocalcemic, and 10%
518
were hypocalcemic based on iCa concentration.
nism is unknown. A correlation between the degree of
Many dogs and cats with CRF have normal serum tCa
hyperkalemia and hypercalcemia was detected when the 147,183,380
concentrations. Hypercalcemia based on mea-
serum potassium concentration was greater than 6.0 to
surement of serum tCa concentration occurs sporadically
6.5 mEq/L, and serum tCa concentration was often 11.4
to 13.5 mg/dL. 178 Increases in serum iCa may or may in dogs and cats with CRF and is usually listed as second
notdevelopinhypoadrenocorticism. 595 SerumtCaconcen- or third in frequency of causes of hypercalcemia in dogs.
Elevated tCa occurs in up to 14% of dogs with CRF, with
tration rapidly returns to normal after 1 to 2 days of 118,183,314,405
corticosteroid replacement therapy in dogs, 442 and IV a range of 12.1 to 15.2 mg/dL. 511 In 71
hypercalcemic cats, CRF was noted in 38%. In cats
volume expansion can return serum calcium concentration
with CRF, the reported incidence of serum total hyper-
to normal within a few hours. Hypoadrenocorticism 147 27
calcemia ranged from 11.5% to 58%.
should always be included in the differential diagnosis of
The incidence of elevated tCa increases with severity of
hypercalcemia, because the clinical signs of hypoadreno-
azotemia. In 73 cats with CRF, serum tCa was increased
corticism and hypercalcemia are similar.
in 8%, 18%, and 32% of those with mild, moderate, or
severe azotemia, respectively. 27 However, increases in
Chronic Renal Failure serum iCa do not show a strong association with the
The findings of hypercalcemia and primary renal azote- degree of azotemia. 134 In 47 of the previous 73 cats with
mia pose a special diagnostic problem because hypercalce- CRF, iCa was increased in 0%, 9%, and 6% of those with
mia can cause renal failure or develop as a consequence of mild, moderate, or severe azotemia, respectively. 27
CRF. Serum PTH concentration is often increased in Hypercalcemia was also not correlated with serum phos-
patients with hypercalcemia related to renal failure, and phorus concentration in dogs with experimental renal
these animals must be differentiated from those with failure. 419,583
primary hyperparathyroidism. Serum iCa concentration The parathyroid glands must be present for hypercal-
is increased in primary hyperparathyroidism but is usually cemia to develop, 583 and partial parathyroidectomy
normal or low in patients with CRF. 118,314 ameliorates hypercalcemia in some dogs with CRF. 183
Deleterious effects of hypercalcemia occur in patients Treatment of dogs with CRF and hypercalcemia with
with renal failure only if it is associated with increases in low-dose calcitriol to reduce PTH synthesis and secretion
serum iCa concentration. Consequently, clinical signs can result in decreased iCa concentration. Low-dose
of hypercalcemia are uncommon in CRF patients, and calcitriol therapy does not appreciably increase intestinal
measurement of serum iCa concentration to assess cal- calcium absorption. 401,402 In patients with CRF,
cium status in CRF patients is critical. In CRF patients, increased serum PTH concentration (renal secondary