Lecture 18 11/12/24 Flashcards
What is a serum iron test?
test that evaluates iron in circulation bound to transferrin
What is a total iron binding capacity test?
test that evaluates plasma’s capacity to carry iron
What is a % saturation test?
calculated result that indicates what % of transferrin molecules are bound by iron
What is a ferritin test?
immunoassay that quantifies plasma ferritin concentrations and correlates to total body stores
What is a bone marrow iron test?
visual qualitative assessment of hemosiderin stored in marrow macrophages
Which test is considered “gold standard” for assessing total body iron stores?
bone marrow iron
What are the characteristics of absolute iron deficiency?
-decreased total body stores of iron
-occurs through chronic external blood loss
Why is it difficult to correct absolute iron deficiency with oral replacement therapy?
only a small amount of iron is absorbed from the GI tract in veterinary species
What are the characteristics of anemia of inflammatory disease?
-hepcidin binds to ferroportin and causes its internalization and degradation
-reduced export of dietary iron into circulation
-sequestration of storage forms of iron occurs in macrophages
How does absolute iron deficiency present on different iron tests?
-decreased serum iron
-normal to increased total iron binding capacity
-decreased % saturation
-decreased ferritin
-decreased bone marrow iron
How does functional iron deficiency/inflammatory iron deficiency present on different iron tests?
-decreased serum iron
-normal to decreased total iron binding capacity
-normal to decreased % saturation
-increased ferritin
-increased bone marrow iron
What are the characteristics of hepatic insufficiency and portosystemic shunts?
-approximately 50% of dogs with PSS have low serum iron and decreased total iron binding capacity
-mechanism is unknown but presumed to be iron sequestration
-ferritin is normal to increased
What can lead to an iron overload?
-hemolytic disease**
-chronic blood transfusions
-excess dietary or parenteral iron administration
Where is PTH sourced from?
parathyroid gland
What are the target organs of PTH?
-bone
-kidney
-intestine
What is the net hormone effect of PTH on plasma conc.?
-increased calcium
-decreased phosphate
Where is vitamin D sourced from?
-GI absorption
-skin metabolism
What are the target organs of vitamin D?
-bone
-kidney
-intestine
What is the net hormone effect of vitamin D on plasma conc.?
-increased calcium
-increased phosphate
Where is calcitonin sourced from?
C-cells of the thyroid gland
What are the target organs of calcitonin?
-bone
-kidney
-intestine
What is the net hormone effect of calcitonin on plasma conc.?
-decreased calcium
-decreased phosphate
Where is FGF23-Klotho sourced from?
bone
What is the target organ of FGF23-Klotho?
kidney
What is the net hormone effect of FGF23-Klotho on plasma conc.?
decreased phosphate
What are the characteristics of free/unbound Ca2+?
-ionized calcium
-physiologically active fraction
-regulated fraction in health
-contributes to pathologic states
What are the characteristics of protein-bound Ca2+?
-80% bound to albumin
-20% bound to globulins
-acts as a storage/buffer pool
-influenced by body pH
What are the characteristics of complexed Ca2+?
-bound to non-protein anions
-anions include citrate, lactate, and phosphate
Which factors affect plasma Ca2+?
-young age
-body protein status
-intestinal absorption
-resorption from bones
-urinary excretion
Which hormones affect plasma Ca2+, and in which direction?
-PTH; increase
-vitamin D; increase
-calcitonin; decrease
What are the causes of hypercalcemia?
-hyperparathyroidism
-osteolysis
-granulomatous disease
-spurious/analytical error
-idiopathic
-neoplasia
-young animals
-Addison’s disease
-renal failure
-vitamin D excess
What are the characteristics of primary hyperparathyroidism?
-occurs due to hyperplasia or neoplasia of parathyroid glands
-increased fCa2+
-increased or within reference interval PTH
What are the characteristics of hypercalcemia of malignancy?
-PTH related protein (PTHrp) behaves like PTH and has similar biologic effects
-PTHrp is secreted by neoplasms such as T cell lymphoma or apocrine gland of the anal sac carcinoma
How does hypoproteinemia lead to hypocalcemia?
-fCa2+ is tightly regulated by hormones
-if protein decreases, calcium is excreted by kidneys or removed to storage pools; it does not shift to fCa2+
What are the characteristics of direct fCa2+ measurement?
-done on blood gas instrument
-use heparinized whole blood
-maintain anaerobic conditions
-measure sample right away
What are the characteristics of primary hypoparathyroidism?
-due to low production of PTH
-low fCa2+
-low or within lower reference interval PTH
-increased or within upper reference interval PO4
-uncommon in vet med
What are the characteristics of hypovitaminosis D/secondary hyperparathyroidism?
-most commonly occurs in CKD patients
-can be seen with nutritional deficiency or chronic GI disease
-low or within lower reference interval fCa2+
-PTH increased or within upper reference interval
What are the characteristics of total calcium measurement?
-done on chem. analyzer
-serum or heparinized plasma sample
-avoid EDTA and citrate anticoagulants
What are the fractions of PO4?
-free; 55%
-protein-bound; 10%
-complexed; 35%
What are the factors that affect plasma PO4?
-young age
-intestinal absorption
-resorption from bones
-urinary excretion
-shifting between compartments
Which hormones affect plasma PO4, and in which direction?
-PTH; decrease
-vitamin D; increase
-calcitonin; decrease
-FGF23-Klotho; decrease
What are the characteristics of phosphate measurement?
-done on chem. analyzer
-serum or heparinized plasma sample
-avoid hemolysis; RBCs contain phosphate, can artifactually increase readout
Why is it important to evaluate calcium and phosphate together?
-sustained hypercalcemia can result in metastatic calcification
-[Ca2+]x[PO4] greater than 70 indicates increased risk of metastatic dysfunction
-concern for renal dysfunction
What are the characteristics of magnesium?
-majority of Mg2+ is intracellular
-1-2% of Mg2+ is in plasma
-fMg2+ is the active fraction
What is the breakdown of Mg2+ plasma distribution?
-55-60% fMg2+
-30-40% protein-bound Mg2+
-4-6% complexed Mg2+
What factors affect plasma Mg2+?
-body protein status
-intestinal absorption
-urinary excretion
-shifting between compartments
Which hormones impact plasma Mg2+, and in which direction?
-PTH; increased
-aldosterone; decreased
-thyroxine; decreased
What are the characteristics of total magnesium measurement?
-done on chem. analyzer
-serum or heparinized plasma sample
-avoid EDTA and citrate anticoagulants
What are the characteristics of free magnesium measurement?
-done on blood gas instrument
-heparinized whole blood sample
-quick, anaerobic handling
-measure sample as soon as possible
