Agreement of Immunoassay and Tandem Mass Spectrometry in the Analysis of Cortisol and Free T4: Interpretation and Implications for Clinicians
Table 1
Descriptive statistics for cortisol (Table 1(a)) and Free T4(Table 1(b)).
(a) Cortisol (mcg/dl) over a 60 minute test period by MS-MS and IA Note that agreement is not universal on reference ranges. However, Reference range for random cortisol by IA in most clinical laboratories = 4 –22 mcg/dl ([23]; see also [24]).
MSMS: MEAN (SD)
IA: MEAN (SD)
cortisol
9.498 (6.08)
8.508 (4.99)
cortisol
21.982 (10.24)
20.553 (8.96)
cortisol
25.758 (12.22)
23.844 (10.74)
(b) Free T4 (FT4, ng/dl) over 3 trimesters of pregnancy, and in nonpregnant women. Note that agreement on reference ranges for FT4 in pregnant women is not universal. Kahric-Janicic et al. (2007) [25] suggest ranges between 0.6 and 1.4 ng/dL for FT4 in pregnant women; results vary by trimester for both MSMS and IA. Reference intervals for FT4 in nonpregnant women by tandem mass spectrometry are 0.8–2.1 ng/dL [24]. Ranges for this analyte in nonpregnant women by IA are lower and have a smaller range, typically around 0.7–1.5 ng/dL [26].
