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Urea and Electrolytes

Title:                            

Ñ  Blood urea

Definition:

Ñ  Normal range :2.5-7.5 mmol/L

Pathogenesis

Pathological Process

Changes in blood urea may be due to:

Ñ  Decreased excretion

Ñ  Increased or decreased production of urea

Ñ  Dilution or concentration of urea due to changes in fluid balance

Causes

Increased blood urea

Decreased excretion

KUS:

Ñ  Renal failure :

Pre-renal

Renal

Post-renal

Increased production

GIT

Ñ  Gastrointestinal haemorrhage

Ñ  High protein diet

E&M

Ñ  Steroid use

Ñ  Fever

IS

Ñ  Burns

Low blood urea

GIT

Ñ  Liver disease

Ñ  Malnutrition

Drugs

Ñ  Over hydration

Toxins

Ñ  Alcohol abuse

 

Title:                            

Ñ  Creatinine

Definition:

Ñ  Normal range:60-110 µmol/L

Pathogenesis

Pathological Process

Causes

Ñ  Serum creatinine may be elevated due to :

Ñ  Renal failure

Ñ  Muscle injury

 

Title:                            

Ñ  Hyponatraemia

Definition:

Ñ  Normal range :137-144 mmol/L

Pathogenesis

Pathological Process

Hyponatraemia may be due to:

Ñ  Salt and water retention with retention of more water than salt

Ñ  Loss of salt and water with loss of more salt than water

Ñ  Syndrome of inappropriate anti diuretic hormone secretion

Causes

Hyponatraemia with hypervolaemia ( retention of salt and water with more water than salt)

CVS

Ñ  Heart failure

KUS

Ñ  Renal failure

GIT

Ñ  Liver failure

Hyponatraemia with hypovolaemia

KUS

Ñ  Diuretic

GIT

Ñ  Vomiting

Ñ  Diarrhoea

IS

Ñ  Burns

E&M

Ñ  Adrenal failure

Hyponatraemia with normovolaemia

E&M

Ñ  SIADH

 

Title:                            

Ñ  Pseudohyponatraemia

Definition:

Ñ  Artefactual decrease in serum sodium due to larger relative proportion of plasma volume occupied by excess of other substances

Ñ  Measured serum osmolality will be normal as the number of particles remains the same

Pathogenesis

Pathological Process

Causes

Pseudohyponatraemia maybe due to excess:

E&M

Ñ  Lipids

Hyperlipidaemia

HS

Ñ  Proteins

Hypergammaglbulinaemia

 

Title:                            

Ñ  Hypernatraemia

Definition:

Ñ  Increased concentration of sodium

Pathogenesis

Pathological Process

Ñ  Hypernatraemia may be due to :

Ñ  Decreased intake of water

Ñ  Increased loss of water

Causes

Decreased intake of water

Ñ  Elderly

Ñ  Disabled

Increased loss of water

Ñ  E&M

Ñ  Diabetes mellitus ( HONK)

Ñ  Diabetes insipidus

 

Title:                            

Ñ  Hyperkalaemia

Definition:

Ñ  Normal range :3.5-4.9 mmol/L

Pathogenesis

Pathological Process

Hyperkalaemia may be due to:

Ñ  Decreased excretion of potassium

Ñ  Shift of potassium from the intracellular compartment to the extracellular compartment

Causes

Decreased excretion of potassium

KUS

Ñ  Renal failure

E&M

Ñ  Adrenal failure

Increased shift of potassium

HS

Ñ  Haemolysis

LMS

Ñ  Rhabdomyolysis

Drugs

Ñ  Tumour lysis syndrome

 

Title:                            

Ñ  Spurious Hyperkalaemia

Definition:

Ñ  Falsely elevated serum potassium

Pathogenesis

Pathological Process

Ñ  This is usually due to leakage of potassium from cells after collection of the sample

Causes

Ñ Difficulty collecting the sample.

Ñ Fist clenched

Ñ  Blood squirted through needle into  bottle causing haemolysis

Ñ Shaking after collection will cause haemolysis

Ñ Wrong anticoagulant, especially potassium EDTA

Ñ Long f storage of specimen

Ñ Excessive cooling of specimen

Ñ Thrombocytosis

Ñ Severe leucocytosis

Ñ Red cell disorders may cause haemolysis

 

Title:                            

Ñ  Hypokalaemia

Definition:

Ñ  Decrease in serum potassium

Pathogenesis

Pathological Process

Hypokalaemia may be due to:

Ñ  Loss of potassium

Ñ  Decreased in take of potassium

Ñ  Transcellular shift of potassium

Causes

Loss of potassium

KUS

Ñ  Renal artery stenosis

Ñ  Renal tubular acidosis

Ñ  Bartter’s syndrome

Ñ  Gitelman’s syndrome

E&M

Ñ  Cushing’s syndrome

Ñ  Conn’s syndrome

Drugs

Ñ  Diuretic use

Ñ  Laxative abuse

Toxins

Ñ  Excessive liquorice

GIT

Ñ  Diarrhoea

Ñ  Vomiting

Ñ  Pyloric stenosis

Ñ  Fistulae

Ñ  Villous adenoma

Decrease intake of potassium

Ñ  Injudicious use of intravenous fluids

Ñ  Malnutrition

Ñ  Parenteral nutrition

Transcellular shift of potassium

E&M

Ñ  Alkalosis

Drugs

Ñ  Insulin and dextrose

Ñ  Beta 2 agonists

Ñ  Theophylline

Ñ  Caffeine

Ñ  Calcium channel blockers

Toxins

Ñ  Glue sniffing 

 

Title:                            

Ñ  Hypermagnesaemia

Definition:

Ñ  Normal range :0.75-1.05 mmol/L

Pathogenesis

Pathological Process

Ñ  Increased ingestion or administration

Ñ  Increased absorption and decreased intestinal excretion due to intestinal hypomotility

Ñ  Decreased excretion due to renal failure

Causes

KUS

Ñ  Chronic renal failure

Ñ  Acute renal failure

LMS

Ñ  Rhabdomyolysis

Ñ  Neoplasm with skeletal muscle involvement

E&M

Ñ  Adrenal insufficiency

Ñ  Diabetic ketoacidosis ( extracellular volume contraction )

Ñ  Hypothyroidism

Ñ  Hypoparathyroidism

Drugs

Ñ  Tumour lysis syndrome

Ñ  Lithium toxicity

Ñ  Treatment of asthma , pre-ecclampsia , cardiac arrhythmias ( overdose)

Ñ  Antacids

Ñ  Laxatives

GIT

Ñ  Hypomotility disorders 

 

Title:                            

Ñ  Hypomagnesaemia

Definition:

Ñ  Decreased serum magnesium

Pathogenesis

Pathological Process

Ñ  Decreased intake

Ñ  Decreased absorption

Ñ  Increased renal loss

Causes

GIT

Ñ  Protein calorie malnutrition

Ñ  Malabsoprtion

Ñ  Chronic diarrhoea

Toxins

Ñ  Alcoholism

E&M

Ñ  Hyperparathyroidism

Drugs

Ñ  Long term proton pump inhibitors

Ñ  Diuretics

 

Title:                            

Ñ  Hyperchloraemia

Definition:

Ñ  Normal range :95-107 mmol/L

Pathogenesis

Pathological Process

Causes

E&M

Ñ  Metabolic acidosis

Ñ  Hyperparathyroidism

Ñ  Hypernatraemia

KUS

Ñ  Renal tubular acidosis

Ñ  Dehydration

GIT

Ñ  Prolonged diarrhoea

Ñ  Loss of pancreatic secretion

Ñ  Ileal loop

Ñ  Ureterosigmoidostomy

Drugs

Ñ  Acetazolamide

Ñ  Excess intravenous saline

 

Title:                            

Ñ  Hypochloraemia

Definition:

Ñ  Decreased chloride in serum

Pathogenesis

Pathological Process

Ñ  Occurs in association with metabolic alkalosis

Causes

GIT

Ñ  Vomiting

Ñ  Intestinal obstruction

E&M

Ñ  Addison’s disease

 

Osmolality

Ñ  Number of particles dissolved in a kg of solution (mosm/kg)

Osmolarity

Ñ  Number of particles dissolved in a litre of solution ( mosm/L)

Calculated plasma osmolarity

Ñ  2[Na⁺+K⁺] + [glucose] + [urea]

 

Title:                            

Ñ  Increased osmolality

Definition:

Ñ  Osmolality greater than 280-295 mosm /kg

Pathogenesis

Pathological Process

Ñ  Either increased solute or decreased solvent

Causes

E&M:

Ñ  Diabetes mellitus (HONK)

Ñ  Diabetes insipidus

GIT

Ñ  Decreased intake of water:

Elderly

Disabled

 

Title:                            

Ñ  Decreased osmolality

Definition:

Ñ  Plasma osmolality less than 280-295 mosm/kg

Pathogenesis

Pathological Process

Ñ  Decreased solute or excess solvent

Causes

Ñ  See causes of hyponatraemia ( sodium is the main solute contributing to osmolality )

 

Title:                            

Ñ  Osmolar gap

Definition:

Ñ  Difference between measured osmolality and calculated osmolality

Ñ  Normal 10-15 mOsm/kg of H₂O

Pathogenesis

Pathological Process

Ñ  Reflects the presence of excess unmeasured solute

Causes

Ñ  Hyperproteinaemia

Ñ  Hypertriglyceridaemia

Ñ  Ethanol

Ñ  Methanol

Ñ  Ethylene glycol

 

 

 

 

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