Jordyn A. Moore¹
Specialist Biochemistry, Canterbury Health Laboratories, Health NZ

Proteins are large, complex biomolecules that are essential for cell processes, and are critical biomarkers for disorders and disease. Time-of-flight (TOF) mass spectrometry coupled with reversed phase chromatography is a powerful analytical technique that can provide detailed structural information for intact proteins. Accurate, well resolved protein masses and mass changes can be interpreted to identify proteins and protein variants, post translational modifications including glycosylation, as well as non-enzymatic reactions like glycation. We have implemented several top-down TOF mass spectrometry methods in our laboratory for analysing intact blood proteins. These include variant identification methods for haemoglobin, fibrinogen and albumin, which are used for screening and diagnosis of haemoglobinopathy and thalassaemia, hypo/dysfibrinogenaemia and familial dysalbuminaemic hyperthyroxinaemia (FDH) respectively. As well as methods that focus on interpretation of minor protein masses, such as the glycosylation pattern of transferrin or apolipoprotein CIII, where the structural detail provides a more effective approach to screening a subset of congenital disorders of glycosylation (CDG). Most recently, we validated a glycated albumin TOF mass spectrometry method as an alternative measure of glycaemic control in patients with unreliable HbA1c measurement. In all cases, TOF mass spectrometry has complimented other screening methodologies, or its superiority has changed our laboratory workflow. 

Lucy Ding¹, Luka McDonald
¹NSW Health Pathology

Accurate thyroglobulin (Tg) measurement is essential for monitoring recurrence in patients with differentiated thyroid cancer (DTC) post-thyroidectomy and radioactive iodine ablation. Traditional immunoassays (Tg-IA) are prone to interference by anti-thyroglobulin antibodies (TgAbs), affecting about a third of patients with DTC and potentially causing falsely low or undetectable Tg levels. This interference can result in under-treatment or unnecessary investigations. NSW Health Pathology has developed a Thyroglobulin by Mass Spectrometry (Tg-MS) assay, the first of its kind in Australasia, to reliably quantify Tg even in the presence of TgAbs.

A clinical validation study at Royal North Shore Hospital will evaluate Tg-MS in addressing the limitations of Tg-IA. Patients with detectable TgAbs will undergo Tg-MS alongside Tg-IA measurements over 12 months. For those with discordant results between methods, data from imaging, biopsies, and other investigations will be used to determine which assay better predicts structural disease and assess the impact on clinical management. If successful, Tg-MS could reduce unnecessary investigations, provide reassurance, and enable timely treatment escalation, improving care for patients affected by TgAb interference.

In current practice, patients vitamin D status is assessed by measuring 25(OH)D and interpreting the results against fixed cut-offs of either 50 or 75 nmol/L. However, widely used immunoassay are known for the variable analytical performance and clinical studies indicate that a substantial number of individuals with 25(OH)D serum levels below the cut-offs for deficiency have actually no metabolic or clinical signs of vitamin D deficiency. With the advent of liquid chromatography-tandem mass spectrometry (LC-MS/MS), the accurate quantitation of 25(OH)D and other vitamin D metabolites, such as 24,25(OH)₂D with gold standard technology becomes increasing accessible to clinical laboratories. The possibility of measuring additional vitamin D metabolites allows the assessment of vitamin D status on a functional level. In this presentation it will be shown how the simultaneous measurement of 25(OH)D and 24,25(OH)2D can improve diagnostics in specific patients groups where the established cut-offs are not applicable and where immunoassays fail to deliver accurate results. Finally, a novel approach to diagnose functional vitamin D deficiency will be presented.