SERUM MAGNESIUM

Elevated
• Renal insufficiency.

Decreased
• Acute fluid loss from GI tract
• Chronic alcoholism
• Chronic hepatitis
• Chronic renal loss
• Hypervitaminosis D.

SERUM PHOSPHORUS: INORGANIC
Normal
Children – 4 to 7 mg/100 ml
Adults – 3 to 4 mg/100 ml.
Elevated
• Renal insufficiency
• Hypoparathyroidism
• Hypervitaminosis D

Decreased
• Hyperparathyroidism
• Rickets and osteomalacia
• Steatorrhoea
• Antacid ingestion.

SERUM CALCIUM
Normal 9.6 to 10.9 mg/100 ml.
Raised
• Hyperparathyroidism (20 mg%)
• Hypervitaminosis D (17 mg%)
• Multiple myeloma
• Cushing’s syndrome.

Decreased
• Hypoparathyroidism
• Osteomalacia, rickets
• Malabsorption syndrome
• Acute pancreatitis.

1. Fluid OverLoad;

• IV fluid administration in excess of the child’s needs
• Nephrotic syndrome
• Cirrhosis
• Heart Failure
• Acute/ Chronic Renal Failure
• Obstructive uropathy

2.Euvolaemic

• Administration of enteral hypotonic fluids (including dilute formula, Oral Rehydration Solutions, excessive water intake)
• Psychogenic Polydipsia
• Increased ADH secretion
  • Pulmonary: pneumonia, bronchiolitis,  mechanical ventilation
  • CNS: infections, injury, tumour
  • Post-operative, trauma, pain
  • Endocrine: Hypothyroid, low cortisol
• Medications
  • Chemotherapy (cyclophosphamide, vincristine, platinum based agents)
  • Antiepileptics (valproate, carbamazepine, oxcarbazepine)
  • Vasopressin

3. Dehydrated

• GI losses and rehydration with free water
  • Gastroenteritis
  • Secretory/osmotic diarrhoeas
  • Ostomies
• Skin losses (CF / burns)
• Abdominal 3rd spacing
• High rate fluid consumption post exercise
• Hyperglycaemia 
• Renal Losses
  • Thiazide Diuretic
  • Cerebral salt wasting
• Primary renal Tubular Disorders
• Hypoaldosteronism
• Metabolic alkalosis

1.Water deficit

Common:

• Gastrointestinal loss eg diarrhoea, stomal losses
• Skin loss (excess sweating/burns)
• Renal losses eg osmotic diuretics, diabetes mellitus, polyuria of acute tubular necrosis
• Inability to obtain water, including breastfed babies due to inadequate milk supply

Less Common:

• Diabetes insipidus (central, nephrogenic, systemic disease, drugs)
• Increased insensible losses
• Impaired thirst mechanism secondary to underlying neurological abnormalities or hypothalamic dysfunction

2.Sodium Excess

• Ingestion of high sodium (inappropriate formula concentration, high osmolality rehydration solutions, salt poisoning)
• Iatrogenic (hypertonic saline, sodium bicarbonate)
• Hyperaldosteronism
  • Primary (Conn’s)
  • Secondary (CCF, nephrotic syndrome, steroids)

1.Decreased intake

Illness

Fasting

Prolonged IV fluids not containing potassium

Eating disorder

2.Increased losses

Gastrointestinal

• Vomiting
• Diarrhoea
• Fistula

Renal

• Diuretics
• Osmotic diuresis
• Aldosterone excess
• Mineralocorticoid excess
• Congenital disorders
• Renal artery stenosis

3.Transcellular shifts

Alkalosis

Hypomagnesaemia

Hypernatraemia

Glucose/insulin infusion

Diabetic ketoacidosis

Refeeding syndrome

4.Medicines

Loop diuretics (eg  frusemide)

Thiazide diuretics

Amphotericin

Cisplatin

Insulin

Salbutamol

Adrenaline  

1.Increased potassium intake

• High potassium load from intravenous fluids or total parenteral nutrition (TPN).
• Blood transfusion.
• Drugs containing a large amount of potassium.
• In children with normal renal function and hormonal mechanisms dietary intake should not cause significant hyperkalaemia.

2.Movement of potassium from intracellular to extracellular space

• Cellular injury - eg, rhabdomyolysis, trauma, burns, severe haemolysis, tumour lysis syndrome.
• Metabolic or respiratory acidosis.
• Hyperkalaemic periodic paralysis.
• Insulin deficiency.
• Drugs - eg, beta-blockers.

3.Impaired renal excretion of potassium

• Chronic kidney disease (CKD) or acute kidney injury (AKI).
• Dehydration, hypovolaemia.
• Aldosterone deficiency: primary adrenal insufficiency, congenital adrenal hyperplasia, aldosterone synthase deficiency.
• Aldosterone resistance: pseudohypoaldosteronism, renal tubular acidosis.

4.Pseudohyperkalaemia

• Prolonged tourniquet time; difficulty collecting the sample.
• Haemolysed blood sample.
• Hereditary spherocytosis and familial pseudohyperkalaemia (potassium leaks from cells as a result of cooling).
• Use of the wrong anticoagulant, especially EDTA contamination of the blood sample.
• Excessive cooling of a specimen.
• Length of storage of the specimen.
• Marked leukocytosis and thrombocytosis.
• Hyperventilation - eg, due to crying. Acute respiratory alkalosis may cause potassium to shift out of cells.
• Sample from arm receiving intravenous fluids containing potassium.