MOLECULAR DIAGNOSTICS :: MASS SPECTROMETRY
Bringing down barriers to give better access to mass spectrometry in the clinical laboratory
By: Mikko Salonen and Peter Cooke H
ave you ever wanted to either implement or expand the use of liquid chromatography – tandem mass spectrometry (LC-MS/MS) in your clinical lab but have put off doing so because of the apparent complexity and expertise needed? You’re not alone. Optimal application and expansion of LC-MS/MS in the clinical laboratory can bring a number of benefits, but that ex- pansion depends on overcoming several long-standing barriers.
Benefits of LC-MS/MS
LC-MS/MS has long been recognized as an important and powerful measurement technology due to its enhanced specificity, accuracy, and precision as compared to im- munoassays.1
It is able to address various
cross-reactivities or interferences com- monly seen with other methodologies, and
for the quantification of small molecules in human sample materials, it is a particularly good solution.2
The most prominent ap-
plications and indeed benefits for clinical LC-MS/MS in measuring and reporting patient results are for small molecule analytes in the areas of endocrinology, hormone measurements, immunosup- pressant, and therapeutic drug monitoring and drugs of abuse testing. There is little argument that these techniques provide a higher level of sensitivity and specific- ity for many analytes compared to other analytical techniques and that patient care has benefited from its use.1 25-hydroxyvitamin D (25(OH)D) pro- vides good examples of the benefits of enhanced analytical and clinical quality of LC-MS/MS. Under-recovery of the 25(OH) D2 component of total vitamin D, and cross-reactivity of the C3-epimer forms
of 25(OH)D, as well as cross-reactivity of the (24,25(OH)2D metabolites with various automated immunoassays are 3 meaning- ful examples that have been studied.3-9
In
the field of neonates and infants, those needing to have their vitamin D status monitored showed mean concentrations of the C3-epimer of between 10% to 61% of the total Vitamin D concentration.5 Assays for immunosuppressant drugs,
which require close monitoring of patient drug concentrations for several reasons, offer another good example of the general accuracy advantages of LC-MS/MS. The bias of the results reported for different im- munoassays compared to LC-MS/MS pro- cedure varies widely. Immunoassays can exhibit interferences due to cross-reactivity with other drugs and metabolites, reactions with heterophilic antibodies, antibodies di- rected against the binding antibody, and the effects of endogenous factors such as hema- tocrit, albumin, bilirubin, and triglycerides.10 The structure of immunosuppressant drug metabolites is similar to the parent drug; therefore, it is difficult if not impossible to construct an immunoassay that recognizes the parent compound without some degree of cross-reactivity towards one or more of the metabolites. LC-MS/MS assays have been developed for immunosuppressants and are widely used in clinical practice. The chromatographic conditions can be estab- lished such that none of the metabolites interfere with the quantitation of the parent drug in the assay.11
Figure 1. Current status of LC-MS/MS workflow. The typical time taken for each step of current LC-MS/MS platform workflows. Times are based on a one-batch sample for a 96 well plate.12
20 AUGUST 2022
MLO-ONLINE.COM
Barriers to LC-MS/MS use Despite these benefits, LC-MS/MS has been inaccessible for many clinical labs and, for labs that have implemented it, challenging to expand and optimize its utilization. Current mass spectrom- etry practice does not necessarily fit the overall workflow in a clinical laboratory.12 It involves multiple manual steps and batch processing, and therefore, assur- ing consistency between instruments over time can be problematic (Figure 1). Mul- tiple instruments and software need to be individually acquired and assessed and put together as connected components. The throughput is lower than other chem- istry or immunoassay analyzers in clinical
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