Principles of diagnostics

Question 1

What are Anticoagulants 1?

Answer 1

1.Ethylenediamine tetra-acetic acid (EDTA), sodium or potassium salt. Prevent clot formation by binding calcium in blood. Used for routine haematology because it preserves the cellular components original size and shape.

2. Trisodium citrate works by binding calcium but its effects are reversible by the addition of calcium ions and it is therefore used for Coagulation studies in Haematology

Question 2

What are Anticoagulants 2?

Answer 2

Heparin (sodium, potassium, lithium or ammonium salts of mucoitin polysulfuric acid). Prevents clot formation by accelerating the action of antithrombin III, which neutralises the action of thrombin. General use in chemistry (lithiumsalt only), especially for urgent samples where clotformation may slow assay or block analyser.

Question 3

What are Anticoagulants 3

Answer 3

*Oxalates- Sodium, potassium, ammonium and lithium salts inhibit coagulation by forming insoluble complexes with calcium. Used with sodium fluoride for glucose, alcohol and lactate measurements.

• Sodium fluoride inhibits enzyme systems involved in glycolysis.
• Sodium polyanethol sulfonate (SPS) inhibits the antibacterial effect of serum and phagocytes and may be added to blood cultures.

Question 4

Examples of fixatives?

Answer 4

1. 10% Formalin (formaldehyde dissolved in water). Acts by forming cross-links between proteins. This renders the proteins insoluble and stabilises cell structure and prevents loss of cell constituents.

2.Ethanol

Question 5

What is diagnostic Sensitivity?

Answer 5

The diagnostic sensitivity tests measures of how well it detects patients with the named disease.

Diagnostic Sensitivity = True Positives x 100(True Positives + False Negatives)

Question 6

What is Diagnostic Specificity?

Answer 6

The diagnostic specificity of a test is a measure of how well it detects patients without the named disease.

Diagnostic Specificity = True Negatives x 100(True Negatives + False Positives)