Case 3

The results suggest that the primary problem is hypercalcemia, which is likely the reason for the clinical signs the owner has noted. The ALP activity is mildly elevated, but the elevated calcium concentration is far more dramatic, so focusing there first makes sense.

Note the hyposthenuric urine. In a patient with normal renal function, we would expect the kidneys to produce a hyposthenuric urine if the patient is drinking excessive amounts of water.

In patients with hypercalcemia, the PU/PD is thought to result from decreased responsiveness to and impaired receptor binding of antidiuretic hormone, leading to polyuria and compensatory polydipsia.

A note about formulas to correct or adjust the calcium concentration: Recent research in this area has shown that calculations to adjust total calcium for albumin/total protein are no longer useful, so they are no longer used.1,2 The best way to verify that the hypercalcemia is real (and not due to changes in pH, protein binding, or other factors) is to assess the ionized calcium fraction-the biologically active form of calcium in the body.

QUESTION 3

In which of the following conditions would you not expect to see an elevated calcium concentration?

a) Hyperparathyroidism

b) Hypoadrenocorticism

c) Diabetes insipidus

d) Neoplasia

e) Vitamin D toxicosis

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