MAGNESIUM

Magnesium

4th most abundant cation, 2nd major intracellular cation

bone

muscles, organs, soft tissues

Magnesium

53% in the _, 46% in _, _, and _ _

serum

RBC

albumin

Magnesium

<1% in _ and _ (⅓ bound in _)

Neuromuscular

Cardiac

enzyme

K+, Ca++, and CHON

Vasodilator

Magnesium

Functions:

_ activity

_ contraction

Part of _ activation (cofactor)

Utilization of _, _, and _ (proteins)

_ (pregnant women) → decreased uterine hyperactivity and eclamptic states wherein it increases uterine blood flow

feces

kidneys

Magnesium

Functions:

Majority are being excreted in the _ (60%) and 40% through the _

calcium, sodium

Regulation of Magnesium

Mg regulation is related to that of _ and _

Mg can be sourced from our diet

Nuts, dry cereals, vegetables, meat, fish, and fruits

25-30%

Regulation of Magnesium

Kidney (percentage)

0.60 to 0.85 mmol/L

Regulation of Magnesium

The renal threshold for Mg2+ is approximately _-_ _ (extracellular)

proximal convoluted tubule

Regulation of Magnesium

Reabsorbs Mg by the _ _ _

PTH

Regulation of Magnesium

Increases renal reabsorption of Mg

PTH

Regulation of Magnesium

Enhances intestinal reabsorption of Mg in the intestine

Aldosterone

Regulation of Magnesium

Increases renal excretion of Mg

hospitalized individuals in the ICU

Hypomagnesemia is most frequently observed in ?

Tubular disorder

Glomerulonephritis

Pyelonephritis

Causes of Hypomagnesemia

Renal excretion (3)

Hyperparathyroidism

Hyperaldosteronism

Hyperthyroidism

Hypercalcemia

Diabetic ketoacidosis

Causes of Hypomagnesemia

Endocrine excretion (5)

Diuretics

Antibiotics

Cyclosporine

Digitalis

Causes of Hypomagnesemia

Drug-induced excretion (4)

Malabsorption syndrome

Surgical resection of small intestine

Nasogastric suction

Vomiting

Diarrhea

Laxative abuse

Neonatal

Primary

Congenital

Causes of Hypomagnesemia

Decreased Absorption (9)

Poor diet/starvation

Prolonged magnesium-deficient intravenous therapy

Chronic alcoholism

Causes of Hypomagnesemia

Reduced Intake (3)

Excess lactation

Pregnancy

Causes of Hypomagnesemia

Miscellaneous Causes (2)

Asymptomatic

Symptoms of Hypomagnesemia

Paralysis and comatose

Symptoms of Hypomagnesemia

Severe (2)

Acute or chronic renal failure

Hypothyroidism

Hypoaldosteronism

Hypopituitarism (decreased growth hormone)

Causes of Hypermagnesemia

Decreased Excretion (4)

Antacids

Enemas

Cathartics

Therapeutic

Causes of Hypermagnesemia

Increased Intake (4)

Dehydration

Bone carcinoma

Bone metastases

Causes of Hypermagnesemia

Miscellaneous Causes (3)

Dehydration

Causes of Hypermagnesemia

can cause pseudohypermagnesemia

Bradycardia

Nausea

Lethargy

Symptoms of Hypermagnesemia (3)

Serum

Plasma (lithium/ammonium heparin)

24-hour urine Mg2+

Specimen Collection

Specimen (3)

HCl

Specimen Collection

24-hour urine Mg2+ – acidified with _ to avoid precipitation

Hemolysis

Specimen Collection

Interferences

False increase because Mg2+ is 10x greater inside RBC

Oxalate, citrate, and EDTA

Specimen Collection

Interferences

anticoagulants are unacceptable – false decrease

Calmagite

Formazan Dye

Methylthymol Blue

Methods of Measurement

Most common colorimetric methods for serum Mg (3)

reddish-violet (532 nm)

Methods of Measurement

Calmagite color and wavelength

660 nm

Methods of Measurement

Formazan Dye wavelength

Dye Lake Method

Clayton Yellow

Thiazole Yellow

Methods of Measurement

Titan Yellow other names (3)

red lake colloidal precipitate

Methods of Measurement

Titan Yellow color

fluorescence (380-410 nm)

Methods of Measurement

Fluorometric Method result and wavelength

Atomic Absorption Spectroscopy

Methods of Measurement

reference method

Polyvinyl chloride membrane

Methods of Measurement

Ion Selective Electrode

25

free ionized

Magnesium Testing Limitations

_% of Mg2+ is protein bound, total Mg2+ may not reflect the physiologically active, _ _ Mg2+

serum

Magnesium Testing Limitations

Mg2+ is an intracellular ion, _ concentrations will not necessarily reflect the status of intracellular Mg2+