Assessment of thyroid function in intensive care unit patients by liquid chromatography tandem mass spectrometry methods

OBJECTIVES

Patients with non-thyroidal illness syndrome have many abnormalities in thyroid hormone tests. Such patients have medical comorbidities associated with low serum proteins and are on multiple medications that interfere with thyroid hormone measurement by immunoassay platforms. It is unknown if these thyroid hormone measurements reflect physiologic conditions or if they are artifacts of testing methodology.

METHODS

Fifty patients were selected from the intensive care unit (ICU) from our institution. Total and free thyroid hormones in plasma were measured by gold standard liquid chromatography-tandem mass spectrometry (LC-MSMS). The results were compared to the Roche Cobas 6000. Patient medical comorbidities and binding protein levels were assessed.

RESULTS

Concentrations of total 3,5,5'-triidothyronine (TT3) and total thyroxine (TT4) were significantly more likely to be low by LC-MSMS compared to immunoassay. Free 3,5,5'-triidothyronine (FT3) levels were similar by immunoassay and LC-MSMS. However, FT4 concentrations were mildly elevated for many patients when measured by ultrafiltration LC-MSMS (19/50, 38%) compared to 1/50 (2%) when measured by immunoassay (p=0.0001). Decreased albumin and thyroxine binding globulin were common and patients were on an average of 11.7±5.0 medications, all factors known to interfere with results found on immunoassays.

CONCLUSIONS

Marked discrepancies in thyroid hormone measurement were noted between reference LC-MSMS and a common immunoassay platform. It is hypothesized that T4 binding to low affinity albumin is displaced by several drugs, raising concentrations of FT4 by LC-MSMS compared to immunoassay, and that the immunoassay values are falsely decreased due to low binding proteins in our patient population.

An improved micro-method for the measurement of steroid profiles by APPI-LC-MS/MS and its use in assessing diurnal effects on steroid concentrations and optimizing the diagnosis and treatment of adrenal insufficiency and CAH

Our goals were to (1) develop an improved micro-method usable for neonates for steroid profile measurements and a method to measure androsterone, a key steroid in the recently described androgen backdoor pathway together, with dehydroepiandrosterone and (2) to assess if dehydroepiandrosterone diurnal concentration fluctuations exist potentially necessitating strict adherence to time of blood sample draw and requirement of separate time-dependent reference intervals. Liquid chromatography-tandem mass spectrometry was performed with an atmospheric pressure photoionization source [1]. For each sample 50μL (100μL for the backdoor pathway) of serum was deproteinized by adding 75μL (150μL for the backdoor pathway) of acetonitrile containing the internal standards. After centrifugation, 75μL (150μL for the backdoor pathway) of supernatant was diluted with 250μL of water and injected onto a Poroshell 120 EC-C8 column (SB-C8 column for the backdoor pathway). Within-run coefficients of variation ranged from 2.4 to 10.4% and between-day coefficients of variation from 2.9 to 11.2%. Comparison studies yielded correlation coefficient between 0.97 and 1.00 with recoveries of 90% or greater. Our methods analyze a 9 steroid profile and an additional 2 steroid profile (backdoor pathway) with minimal sample volume (usable in neonates optimizing early diagnosis of endocrinopathies and genetic diseases). Low limits of quantitation make these methods ideal for steroid measurement in women and prepubertal children. As diurnal variations of dehydroepiandrosterone and other steroids [2] concentrations are clinically significant we recommend that separate reference intervals be developed for 8 am, 8 pm, and midnight sample draws. The use of this approach in improving the diagnosis of patients with adrenal insufficiency and congenital adrenal hyperplasia is discussed.