Clinical biochemistry Flashcards
What is the definition of sensitivity and specificity
Sensitivity = ability to detect disease (positive in disease) Specificity = ability to exclude disease (negative in health)
What are examples of biological effects on a sample
Creatinine dependent on muscle mass
Urea dependent on protein intake and hydration status
Cortisol has diurnal variation
Testosterone/oestrogen/PSA dependent on age/gender
What are examples of pre-analytical effects on a sample
Sample identification
Timing of sample collection (e.g. for cortisol)
Sample tube
Infusion arm sampling
What are examples of analytical effects on a sample
Haemolysis
Icteric samples
Lipaemic samples
Bubbles
Compensation is the attempt to turn acid-base status back to normal by what mechanisms
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
How long does respiratory compensation for a primary metabolic defect take to occur
Rapidly
How long does metabolic compensation for a primary respiratory defect take to occur
Slower- 36-72hrs
What does a hyperkalaemia cause
Acidosis
What does a hypokalaemia cause
Alkalosis
List causes, compensation, correction and features of respiratory acidosis
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
List causes, compensation, correction and features of respiratory alkalosis
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
List causes, compensation, correction and features of metabolic acidosis
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
List causes, compensation, correction and features of metabolic alkalosis
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