Calcium, Magnesium, Phosphorus Flashcards Preview

Clinical Chemistry > Calcium, Magnesium, Phosphorus > Flashcards

Flashcards in Calcium, Magnesium, Phosphorus Deck (37)
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1

Magnesium general (Mg2+)

1.26-2.10 mEq/L
intracellular cation : most in bone or tissue
61% is in free form; the rest is bound to protein or complexed to phophate ion etc

2

Magnesium functions

cofactor for >300 enzymes
involved with DNA & RNA mechanisms
important clinically for cardiovascular, metabolic & neuromuscular disorders

3

Magnesium Regulation

GI aborbs 20-65% of diet Mg2+
Mg bound to protein is filtered by kidney & mostly reaborbed in the loop of Henle
hormones like PTH, Aldosterone, & T4

4

PTH on Mg2+

parathyroid hormone has effect on calcium metabolism & will increase absorption of Mg in the GI & Kidneys

5

Aldosterone on Mg2+

aldosterone focuses on conserving Na+ > Mg2+ & will cause a decrease in absorption

6

Thyroxine on Mg 2+

T4 thyroid hormone is active in metabolism and will require elements like iron etc > Mg & cause a decrease in Mg 2+ absorption

7

Hypomagnesemia

decrease in Mg2+
malabsorption/malnutrition
renal diseases: excess excretion of Mg2+
drugs: diuretics, gentamycin, cisplastin, cyclosporine etc
lactation
endocrine disorders

8

Hypermagnesemia

increase Mg2+
endocrine disorders: hypothyroidism, hypoaldosterone, hypopituitarism
excessive intake
dehydration
renal failure: chronic/acute renal failure: Mg decreased excretion
cardiovascular symptoms

9

Magnesium analyzer methods: specimen

specimen: non-hemolyzed (Mg is intracellular)

10

Magnesium analyzer -non clinical methods

limitations of Assay: protein binding of 25% of Mg & serum may not reflect intracellular concentrations of Mg
Atomic Absorption: reference method, not clinical
hollow cathode lamp - analyte will absorb light & detector detects difference
Lanthanium-HCl diluent: separate analyte of interest away from its bound protein

11

Magnesium analyzer clinical methods

Colorimetric : dyes include calmagite (!), formazen dye, methylthymol blue, & magon
polyvinylpyrrolidine & p-only-phenol are added to remove protein interferences
KOH to make solution alkaline

12

Calmagite

uses EGTA & Cyanide to bind Ca2+ & other metals
Calcium is an interference in colorimetric analyzer method for Magnesium

13

Calcium general

8.4-10.2 mg/dL
bone calcium- 99%
ionic calcium is the active form:
neuromuscular- troponin & Ca2+ involved in muscle contraction
blood coagulation
activates some enzymes
cAMP needs Ca2+

14

Calcium in serum (2 groups)

non-diffusible, protein bound calcium - 40% of blood calcium
diffusible, free calcium (ionic)- ionized free calcium & complexes with phophates, bicarbonate, sulfates etc

15

PTH on Calcium Regulation

parathyroid hormone affects bone calcium to enter circulation
increases GI absorption of calcium
makes kidney conserve Ca2+

16

Vitamin D on calcium regulation

Vit D to 25-OH-cholecalciferol in liver is then converted to 1, 25-Dihydroxy-cholecalciferol by kidney enzyme
this then enhances Ca2+ reabsorption from the GI

17

Calcitonin on calcium regulation

comes from the C cells of the thyroid
inhibits PTH & Vit D
puts calcium back into the bones

18

Hypocalemia

decreased ca2+
hypoparathyroidism (vv ionized ca2+)
hypomagnesium, hypoalbuminemia, pancreatitis, renal disease, etc etc etc
most of these are protein issues & the protein bound Ca would be significantly decreased

19

Hypercalemia

increased Ca
hyperparathyroidism
cancers
hyperthyroidism
drugs:
thiazides, diuretics- increase Ca reabsorption from kidney
biphosphanates- lower ca in blood & put it back into bones (menopausal women)

20

Calcium analyzer methods: specimen

serum, plasma in lithium heparin ( EDTA binds Ca!)
ionized Ca collected anaerobically
urines-24 hr preserved in 6M HCl

21

Calcium analyzer methods (3)

colorimetric: o-cresolphthalein method & Arsenazo III (binds to Ca & read spectro)
atomic absorption- reference method
ion selective electrodes

22

O-cresolphthalein method for calcium analysis

dilute HCl, 8-hydroxy quinolone binds to Mg (!), cresolphthalein complex, diethylamin
read at 578 nm

23

Arsenazo III method for calcium analysis

pH: 6
[Na+] acts as positive influence to bind Ca to slide
used on slide chemistry methods (Vitros)

24

Phosphorus functions

energy source when in ATP, phosphorylates glucose, phospholipids of membranes
> 80% is stored in the bone <1% is in serum

25

Most significant regulator of phosphorus

PTH - parathyroid hormone

26

Hypophosphatemia

decrease in phosphorus
occurs in 60-80% of ICU patients w/ sepsis
vit D deficiency, Antacids, Hyperparathryoidism

27

Hyperphosphatemia

acute/chronic renal failure
neonates lacking PTH full development
increased cell breakdown- infections, exercise, intra hemolysis
hypoPTH
acromegaly
lymphoblastic leukemia

28

Specimen for Phosphorus testing

serum or lithium heparin
avoid hemolysis
FASTING
urine should be 24 hr

29

Fiske Barrow Method for Phosphorus

ammonium molybdate reagent - read at 340nm
or
reduce phosphomolybdate complex w/ reducing agents & measure product (blue) at 660mn

30

Parathyroid hormone effect on Ca2+,Mg2+, Phophorus

increases calcium & magnesium
decreases phophorus