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1364 Magnesium Mast Cell Tumor Prognostic Panel

Magnesium
VetBooks.ir Definition Next Diagnostic Steps to Consider Lab Artifacts

Essential nutrient and major divalent cation. if Levels are High • Falsely increased by hemolysis or delayed
Serum total magnesium includes protein bound Evaluate for dehydration, renal function, serum separation
(30%), anion-complexed (15%), and ionized urinary disease; review oral and parenteral • Falsely decreased if anticoagulants that bind
2+
(55%) fractions. supplements; exclude artifact. Mg are used (EDTA, citrate, oxalate)
Synonyms Causes of Abnormally Low Levels Specimen Collection and Handling
Mg, Mg 2+ • Hypoalbuminemia: decreases protein-bound Serum preferred (red top tube); heparinized
2+
2+
Mg ; no effect on [iMg ] plasma (green top tube) may be used. Remove
Physiology • Excess excretion: generally from renal system, serum/plasma from erythrocytes promptly.
Absorbed in small intestine from dietary sources as with diuresis (e.g., renal disease, fluids,
and excreted in urine, feces, and milk. Most diuretics, osmotic diuresis) and diseases that Relative Cost: $
2+
(99%) Mg is intracellular; serum level may not affect renal handling (e.g., diabetes mellitus,
2+
reflect total body Mg. Ionized Mg (iMg ) is the hyperparathyroidism, hyperthyroidism). May Pearls
2+
2+
biologically active form. Kidneys control Mg occur with lactation • Low serum [Mg ] is common in critical
balance; filtered by glomerulus and reabsorbed • Inadequate gastrointestinal (GI) absorption: care settings.
2+
in tubules. Mg is essential for many cellular chronic diarrhea, malabsorption syndromes, • Concurrent hypocalcemia, hypokalemia may
processes, including membrane ion pumps that deficient diet, prolonged anorexia be refractory to therapy until hypomagne-
+
+
control intracellular [K ] and [Ca ]. • Intracellular shifting: administration of semia is corrected.
insulin or glucose • Consider EDTA contamination if result is
Reference Interval • Iatrogenic: magnesium-poor fluids or total unexpected and concurrent hypocalcemia
Dogs and cats: 1.4-2.3 mg/dL; 1.2-1.9 mEq/L parenteral nutrition and hyperkalemia are present.
(0.58-0.95 mmol/L)
Next Diagnostic Steps to Consider AUTHOR: Mary Leissinger, DVM, MS, DACVP
Causes of Abnormally High Levels if Levels are Low EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
• Decreased urinary excretion: decline in GFR Measure serum albumin. Evaluate for renal
of any cause (e.g., prerenal, renal, postrenal) causes, GI disease.
• Drug-induced: excess supplementation (e.g.,
diet, antacids, intravenous), ACE inhibitors, Drug Effects
spironolactone • Decrease: loop and osmotic diuretics, drugs
• Extracellular shifting: may rarely occur with that induce renal tubular injury
2+
severe tissue damage (e.g., rhabdomyolysis, • Increase: administration of Mg -containing
severe hemolysis) and release of intracellular laxatives, antacids, ACE inhibitors, spirono-
stores lactone

Mast Cell Tumor Prognostic Panel

Definition ribosomal RNA, which increase in number Next Diagnostic Steps to Consider
Panel of histochemical stains that identify during cell proliferation. if Levels are High
proliferation markers, genetic mutations, and • Mutations in c-KIT (the proto-oncogene that Stains are prognostic and do not require
staining patterns in mast cell tumors (MCTs) in encodes KIT, the tyrosine kinase receptor) additional diagnostic testing.
a way that increases the precision and accuracy and abnormal cytoplasmic localization of
of the prognosis KIT are associated with more aggressive Lab Artifacts
tumor behavior. Prolonged exposure to formalin (>7-8 weeks)
Physiology • In addition to providing prognostic informa- may alter both immunohistochemical staining
• Histologically, most MCTs in dogs and cats tion, c-KIT mutations indicate favorable and DNA integrity, resulting in false-negative
are of intermediate grade (grade II), with response to tyrosine kinase inhibitors. results. In practice, this is rarely a concern
highly variable treatment response within because tissue specimens are paraffin embedded
this grade. Test panels can help clarify Causes of Abnormally High Levels promptly after fixation, not kept in formalin
prognosis. Increased expression of PCNA, Ki-67, and long-term.
• Proliferating cell nuclear antigen (PCNA) AgNORs and the presence of c-KIT mutation
is a subunit of a DNA polymerase that is and/or increased cytoplasmic expression of KIT Specimen Collection and Handling
expressed at high levels in the S-phase of are indicative of increased potential for aggres- Formalin fixed tissue (biopsy specimen) or
the cell cycle; Ki-67 is a nuclear protein not sive tumor behavior. This is a general result, paraffin blocks
expressed in noncycling cells; and AgNORs and specific median survival times associated
are argyrophilic nucleolar organizational with varying combinations and levels of these Relative Cost: $$$$
regions associated with transcription of results remain to be proven.

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