Principles Of Clinical Chemistry Flashcards
What do clinicians use to confirm the findings of of their physical examinations
Lab diagnostic tests
What are the uses of clinical laboratory
Diagnosis and in the monitoring of the treatment
Screening for disease/ assessing the prognosis
Research into the biochemical basis of disease
Clinical trials of new drugs
What are the most requested biological samples
Urine, faeces
Venous blood (serum or plasma) or arterial blood
Others commonly requested:
- CSF, sputum and saliva, tissue biopsy or cells. Aspirates (pleura fluid, synovial fluid)
Centrifugation is used to separate blood into plasma and serum. What is the difference between plasma and serum
Plasma with all cells removed
Serum = blood with all cells and coagulation proteins removed
Permanent characteristics that must be documented ( allows for accurate interpretation of results)
-age
- sex
- pregnancy
- stage of menstrual cycle
- body size
- ethnic group
- genetic variant
- non - specific illness
- medication
- normal diet/ drink
Other parameters that can be controlled
Recent exercise
Posture during sample retrieval
Interval since last meal
Interval since last dose of drug
Time of day
What can be measured in biological samples as way to pick up any disease
Concentrations or amounts of metabolites: glucose or amino acids
Presence of particular proteins such as troponins in MI
Enzyme activity = alkaline phosphatase for liver disease
What groups can biochemical tests be divided into
1) selective requesting = carried out based on an individuals patient clinical situation. The tests are divided into core and specialised
2) screening tests = used to search for disease without there being any necessary indication that disease is present
Examples of selective testing
One off tests = designed to answer specific questions - does the patient have increased blood urea/glucose concentration. Used to support the diagnosis
Biochemical profiles: information on disease status can be obtained by analysing multiple constituents rather than one. Plasma electrolytes (Na+, K+, Cl- and bicarbonate, urea) liver function tests (serum bilirubin, ALT, AST)
Dynamic function tests - measure the body’s response to external stimulus eg oral glucose tolerance test (to assess glucose homeostasis)
What is the purpose of selective testing
To confirm diagnosis
To aid differential diagnosis
To assess severity of disease
To monitor the progress of disease
To detect complications or side effects
To monitor therapeutic intervention
Will results affect diagnosis? Will results affect treatment? Will results affect prognosis? If answer is NO then test is not appropriate for the patient
What types of variation can occur
1 ) analytical variation = relates to the limitations of the test itself (precision and accuracy of test)
2) biological variation = discrimination between the normal and abnormal results are affected by a variety of physiological factors
Eg sex, age, diet, drugs, pregnancy, medical history and stress
What is sensitivity
how little of the analyte can the method detect (detection limit)
What is specificity
Specificity = how good is the assay at discriminating between the required analyte and substances which interfere with the assay
Types of jaundice
- haemolytic
- cholestatic
- hepatocellular
Cause of acute liver disease
Poisoning
Hepatic failure
Causes of chronic liver disease
Alcoholic fatty liver
Chronic active hepatitis
Primary billiary cirrhosis
What abnormalities are found in jaundice tests
Increased bilirubin
Bilirubin in urine
Increase in ALP
Increase in AST
Prothrombin time is normal
What abnormalities are found in acute liver disease tests
Increase in bilirubin
Increase in ALP
Increase in AST (normal)
Increase in prothrombin time
Decrease in albumin
What abnormalities are found in chronic liver disease
Cirrhosis
Increase in prothrombin time
Biopsy
What is bilirubin
Derived from the break down of haem and excreted into the bile. Blockages in the bile duct lead to bilirubin in the serum and jaundice
What are aminotransferases
AST and ALT sensitive but non-specific markers of general liver damage (shock, toxic injury and hepatitis )
What are alkaline phosphatases
Activity is increased in liver disease due to increase synthesis by the bile canaliculi in response to cholestasis
What is G-glutamyl transpeptidase
GGT is found in the liver and renal tubules but activity is raised in plasma by cholestasis
What is a key feature of chronic liver disease
Hypoalbuminaemia
Increased prothrombin time
What are the less commonly asked for tests
Hormones
Specific proteins
Trace elements
Vitamins
Drugs
Lipids and lipoprotein
DNA analyses
Plasma cholesterol is an estimate of…
LDL
How to find an estimate of HDL
We need to isolate lipoprotein through ultracentrifugation
Or alternative is electrophoresis
Abnormalities in lipoprotein electrophoresis can be used for initial and rapid diagnosis of….
Hyperlipidaemia
What is the new born screening programme
Screens for 9 conditions at 5 days old
Which 9 conditions are screened for in the NBS
1 ) sickle cell
2 ) cystic fibrosis
3 ) congenital hypothyroidism
All below are inherited metabolic diseases:
4) phenylketonuria
5) medium chain acyl-coA dehydrogenase deficiency MCADD
6) maple syrup urine disease MSUD
7) isovaleric acidaemia IVA
8) glutaric aciduria type 1 GA1
9) homocystinuria HCU
What are POCTs
Point of care testing
Tests that are urgent and will affect the immediate management of the patient
Able to carry them out at remote locations such as at the bedside
Always more expensive than same tests performed in lab
