Page 647 - Small Animal Clinical Nutrition 5th Edition

670 Small Animal Clinical Nutrition

VetBooks.ir Table 33-1. Parathyroid hormone (PTH), ionized calcium and 1,25-dihydroxyvitamin D concentrations in different physiologic/disease states.*
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Ionized calcium
States
1,25-dihydroxyvitamin D
PTH
3
Low
High
Apocrine gland tumors of the anal sacs
Low
Chronic renal failure High Low/normal Normal/low
High calcium intake Low High Normal/low
Hypervitaminosis D Low High Normal/high
Hypoparathyroidism Low Low Low
Lymphosarcoma Low High Low
Primary hyperparathyroidism High High Normal/high
*Adapted from Feldman EC, Nelson RW, eds. Canine and Feline Endocrinology and Reproduction, 2nd ed. Philadelphia, PA: WB Saunders
Co, 1996; 455-493. Hazewinkel HAW. In: Bojrab MJ, ed. Disease Mechanisms in Small Animal Surgery, 2nd ed. Philadelphia, PA: Lea &
Febiger, 1993; 1119-1128. Chastain CB, Ganjam VK, eds. Clinical Endocrinology of Companion Animals. Philadelphia, PA: Lea & Febiger,
1986; 192-217.
1991; NRC, 2006). measurements may be needed for accurate interpretation.
Occasionally, serum concentrations of calcium and phospho- Evaluation of other mineral partial clearances may give some
rus may be elevated or decreased during the genesis of DOD. insight into dietary excesses or deficiencies. Analysis of urine
However, absence of calcium or phosphorus perturbations does for markers of bone turnover such as hydroxylysine glycosides,
not rule out a diagnosis of DOD. Conversely, many other dis- free pyridinolines or pyridinoline cross-links of collagen may
ease processes may result in altered calcium or phosphorus prove useful in the future (Eyre, 1996).
homeostasis,which indicates abnormal values are not pathogno-
monic for a diagnosis of DOD (Nap and Hazewinkel, 1994). Measuring and Interpreting Specific
Increased bone remodeling may result in increased serum Laboratory Tests
alkaline phosphatase activity. This parameter is already high in PARATHYROID HORMONE
young, growing animals and may not be a very sensitive indica- Interpretation of serum parathyroid hormone (PTH) con-
tor of ongoing metabolic bone disease. Other enzyme activities centrations from other species has proven that evaluation
in serum are not very useful for diagnosis of DOD. Bio- must be made in conjunction with presenting signs and other
chemical markers of human bone metabolism such as type I biochemical tests such as concentrations of ionized calcium
collagen propeptides, tartrate-resistant acid phosphatase and and 1,25-dihydroxyvitamin D (Table 33-1). PTH values
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osteocalcin are useful in research studies; however, the signifi- may be increased, decreased or normal in DOD depending on
cance for veterinary diagnostics remains to be proven (Robey the etiology. Increased PTH concentrations may be observed
and Termine, 1990). in association with renal disease, vitamin D deficiency and
Serum and urinary assays of bone markers are of interest as states in which insufficient calcium is present in foods. De-
noninvasive alternatives to bone biopsy. Assays that were creased PTH concentrations may be observed when excess
developed for people have been shown to cross-react in dogs. calcium or vitamin D is present in foods, and in other meta-
Serum bone-specific alkaline phosphatase, urinary deoxy- bolic diseases.
pyridinoline and N-terminal telopeptide of collagen were PTH concentration is most accurately measured by a “two-
measured in dogs with commercial enzyme immunoassays site” immunoassay. This assay eliminates interference by mid-
designed for people. Serum osteocalcin and carboxy-terminal region or terminal fragments that are abundant in animal
cross-linked telopeptide of type I collagen were measured serum. Single time-point evaluations of PTH may not prove
with commercial radioimmunoassays. Significant diurnal useful in determining the etiology of DOD. Repeated evalua-
rhythms were identified for osteocalcin, bone-specific alkaline tions may yield more useable information, but are probably not
phosphatase, carboxy-terminal cross-linked telopeptide of cost effective.
type I collagen and urinary deoxypyridinoline. No clear
rhythm was evident for N-terminal telopeptide of collagen. CALCITONIN
Due to the variability in marker excretion in individual ani- Calcitonin, a peptide hormone, is released primarily from C-
mals, the most appropriate use for these assays is as a screen- cells of the thyroid gland in response to sudden increased con-
ing tool for cohort studies, rather than as a diagnostic or prog- centrations of ionized calcium in serum. Calcitonin may also be
nostic tool in individual animals (Ladlow et al, 2002). Breed released in response to other stimuli such as gastrin secretion
effects cannot be excluded; however, for serum alkaline phos- stimulated by food intake (Azria, 1989). Calcitonin is measured
phatase and carboxyl-terminal cross-linked telopeptide of by radioimmunoassay (Hazewinkel et al, 1985, 1999). The test
type I collagen, the concentrations were comparable in giant is not commercially available and rational interpretation re-
and toy breeds and in beagles (Breur et al, 2004). quires multiple sample evaluations. If calcitonin levels are eval-
Urinalysis results are usually within normal limits for animals uated to investigate the etiology of DOD, results should be
with DOD. Advanced techniques, including measurement of compared to normal values for the laboratory and interpreted in
calcium and phosphorus partial clearance ratios, may add conjunction with results of other tests (e.g., PTH, ionized cal-
insight about calcium and phosphorus nutrition, but repeated cium and vitamin D analyses).
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