Chapter 14

Calcium, Magnesium, and Phosphate

，Pan Baishen

Content

CALCIUM• Hypoparathyroidism

• Renal Diseases

• Neonatal Monitoring

• Monitoring in Surgery and Acute Care

• Critically Ill Patients

• Hypomagnesemia

Content

MAGNESIUM • Critical Care

• Cardiac Disorders

• Drug Effects on Magnesium Concentration

• Diabetes Mellitus

• Alcoholism

• Other Diseases

Content

PHOSPHATE • Hypophosphatemia

• Hyperphosphatemia

• The electrolytes calcium, magnesium, and phosphate are the principal inorganic constituents of bone and are vital in the function of membranes, hundreds of enzymes, genetic regulation, muscle contraction, and energy utilization.

CALCIUM-1

• Of all the calcium in the body, 99% is in the bone. The remaining 1% is mostly in the blood and other extracellular fluids.

• Calcium circulates in the blood is several forms:

– 45% to 50% free ionized

– 40% to 45% bound to protein

– 10% to 15% bound to anions

CALCIUM-2

• Three hormones are known to participate in serum calcium regulation, and have rates of secretion that depend on ionized calcium concentration.

– parathyroid hormone (PTH)

– 1,25 dihydroxyvitamin D

– calcitonin

CALCIUM -3

CALCIUM-4

• Calcium in blood is distributed among several forms ：– About 45% circulates as ionized calcium

– 40% is bound to anionic sites on protein

– 15% is bound to anions

HYPOCALCAEMIC DISORDERS

HYPOCALCAEMIC DISORDERS-1

• Hypoparathyroidism – Most cases of hypocalcemia from

hypoparathyroidism result from surgical removal of tissue during parathyroid or thyroid surgery

– Pseudohypoparathyroidism is a condition in which renal cells do not respond to PTH

HYPOCALCAEMIC DISORDERS-2

• Renal Disease – In renal glomerular disease ， ionized

calcium is changed independently of total calcium

– In chronic renal disease, a marked increase in serum PTH levels ,in which phosphate binds calcium, or by altered vitamin D metabolism

HYPOCALCAEMIC DISORDERS-3

• Neonatal Monitoring

– The first type of neonatal hypocalcemia is associated with parathyroid immaturity and usually resolves by the first week of life

– The second type of neonatal hypocalcemia is associated with both hyperphosphatemia and hypomagnesemia

HYPOCALCAEMIC DISORDERS-4

• Monitoring In Surgery and Acute Care

– In open-heart surgery when the heart is restarted

– Administering calcium as a cardiotropic agent before giving drugs

– During liver transplantation

HYPOCALCAEMIC DISORDERS-5

• Critically Ill Patients

– Sepsis

– Thermal burns

– Renal failure

– Cardiopulmonary insufficiency

HYPOCALCAEMIC DISORDERS-6

• Hypomagnesaemia – Inhibition of transport of PTH across the

parathyroid gland membrane

– Impairment of PTH action at its receptor site on bone

– Interference with the action of vitamin D

HYPERCALCEMIC DISORDERS

HYPERCALCEMIC DISORDERS-1

• Primary hyperparathyroidism

– Ionized calcium is elevated more frequently than total calcium in subtle or asymptomatic hyperparathyroidism

– Measuring PTH during operations on the parathyroid glands can determine if sufficient parathyroid tissue has been removed

HYPERCALCEMIC DISORDERS-2

• Malignancy

– PTHRP appears to be expressed in tumors, measurements of which ultimately may have clinical diagnostic value

– Ionized and total calcium measurements have about equal utility in the detection of occult malignancy

CALCIUM-1

• Total calcium determinations may be performed on either serum or heparinized plasma

• In routine testing of serum, many automated analyzers give results that are comparable to atomic absorption. In urine and other fluids, atomic absorption still is preferred.

CALCIUM-2

REFERENCE RANGES FOR CALCIUM

mmol/liter mg/dl

Total calcium

Child 2.20-2.68 8.8-10.7

Adult 2.10-2.55 8.4-10.2

Ionized calcium

At birth 1.30-1.60 5.2-6.4

Neonate 1.20-1.48 4.8-5.9

Child 1.20-1.38 4.8-5.5

Adult 1.16-1.32 4.6-5.3

MAGNESIUM -1

• effect on myocardial function and blood pressure

• an essential activator of over 300 enzymes

• complex of ATP is the substrate in energy production

MAGNESIUM -2

• The average dietary intake of magnesium is 10 to 15 mmol/day

• 20% to 63% of the dietary magnesium can be absorbed in the small intestine

• The overall regulation of body magnesium is controlled largely by the kidney

MAGNESIUM-3

• The human body contains about 1 mol (24 g) of magnesium

– about 50% in the skeleton

– relatively high concentrations in skeletal muscle, liver, and myocardium

HYPOMAGNESEMIA-1

• Critical Care

– Among chronic diseases, alcoholism, liver disease, and carcinoma were commonly associated with hypomagnesemia

– Magnesium was the most common electrolyte abnormality found among pediatric intensive-care unit patients

HYPOMAGNESEMIA-2

• Cardiac Disorders

– Magnesium deficiency has been associated with coronary vasospasm, arrhythmias, acute infarction, and sudden death

– In patients undergoing surgery with cardiopulmonary bypass, plasma ionized magnesium was decreased by 24 hours after bypass

HYPOMAGNESEMIA-3

• Drug Effects on Magnesium Concentration

– Several drugs, including diuretics, gentamicin and other aminoglycoside antibiotics, cisplatin, and cyclosporine result in hypomagnesemia

HYPOMAGNESEMIA -4

• Diabetes Mellitus

– Magnesium loss secondary to ketoacidosis and glycosuria

– abnormal intracellular extracellular distributions of magnesium caused by hormonal imbalances

HYPOMAGNESEMIA -5

• Alcoholism

– Renal magnesium losses and decreased muscle magnesium content

– dietary deficiency, ketosis, vomiting, diarrhea, and hyperaldosteronism

HYPOMAGNESEMIA-6

• Other Diseases

– Pregnancy

– Premature labor and preeclampsia or eclampsia

– Neonatal seizures

– Renal stone formation and other renal calcification

– Paget's disease

MAGNESIUM -1

• The patient should fast before collection of blood

• Hemolyzed samples are not acceptable

• The anticoagulants must not be used

MAGNESIUM -2

• About 30% of magnesium is protein bound, total magnesium may not reflect the physiologically active magnesium

• serum concentration will not necessarily reflect the status intracellular magnesium

MAGNESIUM-3

• Methods:

– atomic absorption spectroscopy

– colorimetric methods using either calmagite or methylthymol blue

– a dry-slide colorimetric method using a formazan dye and a calcium chelator

– A magnesium load test

MAGNESIUM -4

REFERENCE RANGES FOR MAGNESIUM mmol/liter

Total magnesium

　 Serum (newborns) 0.50-0.90

　 Serum (adults) 0.65-1.05

　 Erythrocytes 1.65-2.65

　 CSF 1.0-1.40

　 Urine 1-5 mmol/day

Ionized magnesium

　 Blood 0.44-0.60 (AVI. analyzer)

0.39-0.64 (Nova analyzer)

PHOSPHATE-1

• The genetic materials DNA and RNA are complex phosphodiesterases

• The most important reservoirs of biochemical energy are ATP, creatine phosphate, and phosphoenol pyruvate

PHOSPHATE -2

• About 80% of the 700 to 800 grams of phosphate in the body are contained in bone, mostly in the form of hydroxyapatite [Ca10(PO4)6(OH)2]

• The kidney plays an important role in the regulation of serum phosphate concentration

HYPOPHOSPHATEMIA-1

• Transcellular Shift – the movement of glucose into cells is

accompanied by phosphate • GI losses

– diarrhea and vomiting • Renal losses

– primary hyperparathyroidism, diuretics, hypomagnesemia, or defects in renal tubular absorption of phosphate

HYPOPHOSPHATEMIA-2

• Mixed causes – Diabetic ketoacidosis – Acidosis – Alcoholism

HYPERPHOSPHATEMIA-3

• Renal failure

• Severe infections

• Intensive exercise

• Neoplastic diseases

PHOSPHATE -1

• The patient should fast before collection of blood

• Hemolyzed samples are not acceptable

• Intravenous administration of glucose or fructose lowers serum phosphate

PHOSPHATE-2

• Methods:

Reducing Reagent Absorption Peak

ANS, stannous chloride, ferrous ammonium sulfate

660nm

Semidine HCl 680nm

PHOSPHATE-3

REFERENCE RANGES FOR PHOSPHATE

Serum Phosphate

mg/dL mmol/L

Newborn (1-2 days) 5.5-9.5 1.78-3.07

Infant 4.5-6.5 1.45-2.10

Child 4.5-5.5 1.45-1.78

Adult male 2.3-3.7 0.74-1.20

Adult female 2.8-4.1 0.90-1.32