Standardization of steroid tests and implications for the endocrine community: Author’s reply

I thank Dr Middle and Mr MacKenzie for reminding us of the challenges in running an external quality assurance scheme (EQAS) and of industry resistance to evidence of poor accuracy. ¹ Mr Ducroq draws attention to metrological traceability, ² which was a deficiency of the editorial. That approach has not, however, been widely used. My editorial acknowledged some of the changes in technology leading to improved sensitivity. Mr Ducroq found that the required sample size was much less using liquid chromatography mass spectrometry (LC-MS/MS) instead of a modified reference gas chromatography mass spectrometry (GC-MS) method for assigning accurate concentrations to EQAS samples calibrated with a certified reference cortisol material. This welcome change has permitted the introduction of WEQAS samples with assigned concentrations. Some hospital management decisions drove cost pressures on the laboratory, and automated analytical equipment based on immunoassay was widely introduced, but at the expense of accuracy. The diagnostics industry has responsibilities to better describe elements of their immunoassay tests, although they now thoroughly validate methods against mass spectrometry (MS) calibration. The editorial highlighted other issues beyond EQA. Clinicians, patients and patient support groups have problems in relying on numbers and reference ranges that keep changing. The professional bodies lack guidance and standardization of provocative testing.

MS is an attractive proposition for improved accuracy but poses challenges to hospital laboratory scientists and will not totally replace immunoassays. Training in analytical chemistry, chromatography, gas phase chemistry, physics, electronics, quantitative mass spectrometry and steroid biochemistry is paramount. Validation of such methods is a time-consuming exercise in a busy laboratory programme of work. There are differences at almost every level: sample size, extraction method (protein precipitation, solid phase or liquid-liquid), high-performance liquid chromatography column stationary phase and dimensions, mobile phase, ionization, internal standard, as well as the MS instrument itself. Interference testing is needed for the analyte and the internal standard to exclude the effects of co-eluting substances and related steroids. ³ The patients may be taking synthetic steroids or other drugs that can interfere negatively or positively on the analysis. All these factors will influence the accuracy of the results and hamper harmonization. Focusing laboratory tests for certain analytes, such as steroids, in centres of excellence is an option to be considered. ⁴ The evolution of metabolomics will see newer technology such as high-resolution accurate mass techniques and time-of-flight MS instruments. Steroid measurements will be a part of larger metabolic profiles with interpretation needed from metadata. Laboratory professionals need to consider how best to deliver the service not only in a cost-effective manner but also to meet the needs of patients.