Biochemistry Flashcards
Accuracy
How close the result is to the actual ‘true’ value
Precision
Reproducibility of an analytical result
Reference interval
Typically, the middle 95% of the population shown on the biochemistry graph generate the reference interval. The 2.5% of the population on either side shows an ‘abnormal’ result
Sensitivity
Tells you how good a test is at identifying disease
Specificity
Measure of how good the test is at identifying health
Positive predictive value
The percentage of people with a positive test who have the disease
Negative predictive value
The percentage of people with a negative test who don’t have the disease
Some contributors to pre-analytical variation
Time of day, posture, fasting status, recent exercise, time in transit to laboratory, temperature during transit, anticoagulant or preservative used
The respiratory component and the metabolic component
pCO2 = respiratory component HCO3- = metabolic component
Acidaemia and alkalaemia
Acidaemia = ↑[H+] Alkalaemia = ↓[H+]
Acidosis and alkalosis
Acidosis = ↑[H+] or a process tending to cause ↑[H+] Alkalosis = ↓[H+] or a process tending to cause ↓[H+]
Respiratory acidosis
↑[H+] due to ↑pCO2
Respiratory alkalosis
↓[H+] due to ↓pCO2
Metabolic acidosis
↑[H+] due to ↓HCO3-
Metabolic alkalosis
↓[H+] due to ↑HCO3-
Respiratory vs Metabolic compensation
Respiratory - too much [H+] results in the lungs blowing off CO2
Metabolic - too much CO2 results in the kidneys getting rid of [H+]
Some causes of respiratory acidosis
Choking, bronchopneumonia, chronic obstructive airway disease
Some causes of respiratory alkalosis
Hysterical over-breathing, mechanical over-ventilation, raised intracranial pressure
Some causes of metabolic acidosis
Impaired H+ secretion, increased H+ production or ingestion, loss of HCO3-
Some causes of metabolic alkalosis
Loss of H+ in vomit, alkali ingestion, potassium deficiency
