Page 152 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

142 ELECTROLYTE DISORDERS

methodologies are not available, measurement of serum Normal young growing dogs may have mildly higher
iCa, PTH, and PTHrP may be performed before exten- serum calcium concentrations than older dogs. 385
sive body cavity imaging or bone marrow evaluation.
Measurement of 25-hydroxyvitamin D is useful in cases Transient or Inconsequential
of potential cholecalciferol or ergocalciferol ingestion. Hypercalcemia
Measurement of 1,25-dihydroxyvitamin D (calcitriol) is Inconsequential hypercalcemia does not cause injury,
occasionally useful if excess calcitriol is the cause of hyper- resolves rapidly, or is only mild. Dehydration can result
calcemia. The anticipated changes in calcium hormones in mild hypercalcemia attributed to hemoconcentration.
and serum biochemistry in disorders causing hypercalce- Furthermore, dehydration and volume contraction stim-
mia are noted in Table 6-2. ulate increased sodium and calcium reabsorption in the
kidneys. An increased serum concentration of protein,
NONPATHOLOGIC HYPERCALCEMIA especially albumin, can result in an increased serum tCa
Serum calcium concentrations in animals may be mildly concentration as more calcium binds to protein. Dehy-
increased after feeding; consequently, a 12-hour fast is dration in dogs is occasionally associated with serum
recommended before blood sampling. Laboratory error tCa concentrations of 12.0 to 13.5 mg/dL that rapidly
or detergent contamination of the serum or sample tube return to normal after dehydration is corrected. Increased
may result in artifactual hypercalcemia. 380 Lipemia fre- serum tCa and decreased iCa concentrations can occur
quently causes erroneously high serum tCa transiently after plasma transfusion because of excess
concentrations because of colorimetric interference. citrate-calcium ion complexes. 385

TABLE 6-2 Anticipated Changes in Calcemic Hormones and Serum Biochemistry
Associated with Disorders of Hypercalcemia
1,25 PTG
Corr (OH) ULS,
-
tCa iCa alb tCa Pi PTH PTHrP 25(OH)-D 2 D Surgery
Primary hyperpara- " " N N #N "N N N N " Single "
thyroidism
Nutritional secondary N# N# N N# N" " N #N N # Multiple "
hyperparathyroidism
Renal secondary N #" N# N N " N " N N # N # Multiple "
hyperparathyroidism
Tertiary hyperpara- " " N " " " N N # #N Multiple "
thyroidism
Malignancy Associated
Humoral " " N # " N # N # N " N N #N " #
hypercalcemia
Local osteolytic " " N # " N N " # N N" N N #
Hypervitaminosis D
Cholecalciferol " " N " " N # N " N " N #
Calcitriol " " N " N " # N N " # N
Calcipotriene " " N " " N # N N # N # N
Hypoadrenocorticism " " N # " " N # N N N # N N
Hypervitaminosis A " " N " N # N N N # # N
Idiopathic (cat) " " N " N" # N N N N #" # N
Dehydration " N " " N " N N " N # N N N N
Aluminum exposure " " N " "N # N N N N # N "#
(renal failure)
Hyperthyroidism (cat) " " N " N " N "# N N N # N "
Raisin/grape toxicity " — N " N " — — — — —
(dog)

#, Decreased concentration; ", increased concentration; N, normal; tCa, serum total calcium; iCa, serum ionized calcium; alb, albumin; Corr tCa, corrected
total calcium; Pi, inorganic phosphorus; PTH, parathyroid hormone; PTHrP, parathyroid hormone–related protein; 25(OH)-D, 25-hydroxyvitamin D;
1,25(OH)2-D, 1,25-dihydroxyvitamin D; PTG, parathyroid gland; ULS, ultrasound.