Calcium, Magnesium, Phosphorus Flashcards
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
Magnesium functions
cofactor for >300 enzymes
involved with DNA & RNA mechanisms
important clinically for cardiovascular, metabolic & neuromuscular disorders
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
PTH on Mg2+
parathyroid hormone has effect on calcium metabolism & will increase absorption of Mg in the GI & Kidneys
Aldosterone on Mg2+
aldosterone focuses on conserving Na+ > Mg2+ & will cause a decrease in absorption
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
Hypomagnesemia
decrease in Mg2+ malabsorption/malnutrition renal diseases: excess excretion of Mg2+ drugs: diuretics, gentamycin, cisplastin, cyclosporine etc lactation endocrine disorders
Hypermagnesemia
increase Mg2+
endocrine disorders: hypothyroidism, hypoaldosterone, hypopituitarism
excessive intake
dehydration
renal failure: chronic/acute renal failure: Mg decreased excretion
cardiovascular symptoms
Magnesium analyzer methods: specimen
specimen: non-hemolyzed (Mg is intracellular)
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
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
Calmagite
uses EGTA & Cyanide to bind Ca2+ & other metals
Calcium is an interference in colorimetric analyzer method for Magnesium
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+
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
PTH on Calcium Regulation
parathyroid hormone affects bone calcium to enter circulation
increases GI absorption of calcium
makes kidney conserve Ca2+
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
Calcitonin on calcium regulation
comes from the C cells of the thyroid
inhibits PTH & Vit D
puts calcium back into the bones
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
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)
Calcium analyzer methods: specimen
serum, plasma in lithium heparin ( EDTA binds Ca!)
ionized Ca collected anaerobically
urines-24 hr preserved in 6M HCl
Calcium analyzer methods (3)
colorimetric: o-cresolphthalein method & Arsenazo III (binds to Ca & read spectro)
atomic absorption- reference method
ion selective electrodes
O-cresolphthalein method for calcium analysis
dilute HCl, 8-hydroxy quinolone binds to Mg (!), cresolphthalein complex, diethylamin
read at 578 nm
Arsenazo III method for calcium analysis
pH: 6
[Na+] acts as positive influence to bind Ca to slide
used on slide chemistry methods (Vitros)
Phosphorus functions
energy source when in ATP, phosphorylates glucose, phospholipids of membranes
> 80% is stored in the bone <1% is in serum
Most significant regulator of phosphorus
PTH - parathyroid hormone
Hypophosphatemia
decrease in phosphorus
occurs in 60-80% of ICU patients w/ sepsis
vit D deficiency, Antacids, Hyperparathryoidism
Hyperphosphatemia
acute/chronic renal failure neonates lacking PTH full development increased cell breakdown- infections, exercise, intra hemolysis hypoPTH acromegaly lymphoblastic leukemia
Specimen for Phosphorus testing
serum or lithium heparin
avoid hemolysis
FASTING
urine should be 24 hr
Fiske Barrow Method for Phosphorus
ammonium molybdate reagent - read at 340nm
or
reduce phosphomolybdate complex w/ reducing agents & measure product (blue) at 660mn
Parathyroid hormone effect on Ca2+,Mg2+, Phophorus
increases calcium & magnesium
decreases phophorus
Calcitonin effect on Ca2+ & phosphorus
decreases both Ca2+ & phosphorus in serum
Vitamin D effect on Ca, phosphorus
enhances Ca & Phos absorption & retention
leads to increase
Lactate
byproduct of anaerobic metabolism
liver processes lactate into glucose via gluconeogenesis
measure clinically in critically ill patients: type A & type B
lactate clinical measurements Type A
hypoxic conditions like shock, MI, severe CHF, pulmonary edema or severe blood loss
lactate clinical measurements Type B
metabolic in origin
see in DM, severe infections, leukemia, liver or kidney disease, toxins
Lactate specimen
NO TOURNIQUET
keep specimen on ice
use heparin
Lactate enzymatic method
substrate: lactate
enzymes: lactate oxidase, peroxidase
read: colored product
