Sum activity of peripheral deiodinases

The sum activity of peripheral deiodinases (GD, also SPINA -GD) defines the maximum amount of triiodothyronine, which can be formed under conditions of substrate saturation of thyroxine. It is an approximate value for the activity of 5'- deiodinases outside the CNS.

Determination

In cell culture systems, the Dejodierungsleistung can be determined by the T3 production or Jodfreisetzung substrate saturation is measured with T4.

In vivo SPINA - GD with

Or

Calculated from the serum concentrations of TSH, free thyroxine and free triiodothyronine or bound.

Constant parameters of the equation are:

Dilution factor for T3 ( reciprocal of the apparent volume of distribution, 0.026 l -1): Clearance exponent for T3 (8e -6 sec -1) KM1: dissociation constant of type 1 deiodinase (5e -7 mol / l) K30: dissociation constant T3 - TBG ( 2E9 l / mol)

Reference ranges

The equations and their parameters are calibrated for adults with a body mass of 70 kg and a plasma volume of approximately 2.5 l

Clinical Significance

SPINA - DG correlated in healthy subjects with body mass index and the TSH levels. It is reduced in the case of a Non- thyroidal illness syndrome with Hypodejodierung.