Figure 6. Effects of Nonthyroidal Illness (NTI) on Thyroid Tests. Figure 6a shows the magnitude and direction of changes in total (TT4 and TT3) and free (FT4 and FT3) thyroid hormone IMA tests versus FT4 measured by the RMP (ED-ID-LC-MS/MS), as the severity of illness increases, followed by recovery. Figure 6b shows the magnitude and direction of TSH changes as the severity of illness increases, followed by recovery. Data redrawn from reference 188 with permission.