42. Pre-analytical considerations of the hormone tests.

From greek.doctor
  • Measured by serum in plain tube (red) or gel tube (yellow)
  • Small peptide hormones
    • Unstable, transported quickly and on ice
    • TRH
    • Renin
  • Amino acid derivatives
    • T3, T4
      • Only free fraction is measured
      • Protein binding influences measurement
    • Adrenalin
  • Steroids
    • Cortisol
    • Aldosterone
    • Sex hormones
    • Both fractions are measured
      • Binding protein should also be measured
  • Biological variation
    • GH – pulsatile release
    • Cortisol – influences by stress, diurnal rhythm
    • Should be measured in the morning
    • Log-linear relationship – small change in TRH can cause significant change in TSH
  • Analytical variations
    • Measured by immunoassays
    • Immunoassay interference
      • Heterophilic antibodies – low affinity antibodies
      • Anti-animal antibodies
      • Autoantibodies
      • Antibodies from treatment
      • Rheumatoid factor
    • Matrix effect
      • High level of molecules in plasma -> molecules can cover epitopes of analyte -> underestimate level of analyte
    • High-dose hook effect
      • More analyte than capture antibody -> analyte binds to detection antibody without being captured -> detection antibodies depleted -> fewer captured analytes can be labelled -> false negative result