Clinical biochemistry Flashcards

1
Q

What is the definition of sensitivity and specificity

A
Sensitivity = ability to detect disease (positive in disease)
Specificity = ability to exclude disease (negative in health)
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2
Q

What are examples of biological effects on a sample

A

Creatinine dependent on muscle mass
Urea dependent on protein intake and hydration status
Cortisol has diurnal variation
Testosterone/oestrogen/PSA dependent on age/gender

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3
Q

What are examples of pre-analytical effects on a sample

A

Sample identification
Timing of sample collection (e.g. for cortisol)
Sample tube
Infusion arm sampling

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4
Q

What are examples of analytical effects on a sample

A

Haemolysis
Icteric samples
Lipaemic samples
Bubbles

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5
Q

Compensation is the attempt to turn acid-base status back to normal by what mechanisms

A

Buffering-
Bicarb in serum, phosphate in urine
Skeleton
Intracellular accumulation/loss of H ions

Compensation-
Diametric opposite of the original abnormality
Never overcompensates
Delayed and limited

Treatment-
By reversal of the precipitating situation

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6
Q

How long does respiratory compensation for a primary metabolic defect take to occur

A

Rapidly

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7
Q

How long does metabolic compensation for a primary respiratory defect take to occur

A

Slower- 36-72hrs

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8
Q

What does a hyperkalaemia cause

A

Acidosis

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9
Q

What does a hypokalaemia cause

A

Alkalosis

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10
Q

List causes, compensation, correction and features of respiratory acidosis

A

CAUSES-
Anything that stops gas exchange
Airway obstruction- bronchospasm, COPD, aspiration, strangulation
Respiratory centre depression- anaesthetics, sedative, cerebral trauma, tumours
Neuromuscular disease- Guillain-Barre syndrome, motor neurone disease
Pulmonary disease- pulmonary fibrosis, RDS, pneumonia
Extrapulmonary disease- flail chest

COMPENSATION-
Increased renal acid excretion

CORRECTION-
Requires return of normal gas exchange

FEATURES-
Acute= low pH, high H, normal HCO3, high pCO2
Chronic= low pH, high H, high HCO3, high pCO2

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11
Q

List causes, compensation, correction and features of respiratory alkalosis

A
CAUSES- 
Hypoxia- high altitude, severe anaemia
Pulmonary disease- oedema, embolism
Mechanical overventilation
Increased respiratory drive- salicylates, trauma, infections, tumours, hepatic failure, gram negative septicaemia, primary hyperventilation syndrome

COMPENSATION-
Increased renal bicarbonate excretion

CORRECTION-
Of cause

FEATURES-
Acute= high pH, low H, normal HCO3, low pCO2
Chronic= high pH, low H, low HCO3, low pCO2

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12
Q

List causes, compensation, correction and features of metabolic acidosis

A

CAUSES-
Increased acid formation- ketoacidosis, lactic acidosis, poisoning
Acid ingestion- poisoning
Reduced acid excretion- renal tubular acidosis, renal failure, carbonic dehydratase inhibitors
Loss of bicarbonate- diarrhoea, pancreatic/intestinal/biliary fistula

COMPENSATION-
Hyperventilation

CORRECTION-
Increased renal acid excretion

FEATURES-
Low pH, high H, low HCO3, low pCO2

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13
Q

List causes, compensation, correction and features of metabolic alkalosis

A

CAUSES-
Increased loss of acid- vomiting
Increased renal H excretion- diuretics, mineralocorticoid excess

COMPENSATION–
Hypoventilation with CO2 retention

CORRECTION-
Increased renal bicarbonate excretion, reduced renal protein loss

FEATURES-
High pH, low H, high HCO3, normal pCO2

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