Tandem Mass Spectrometry For Diagnosis Research Articles

The role of tandem mass spectrometry in the diagnosis of inherited metabolic diseases

This paper reviews the clinical applications of tandem mass spectrometry in diagnosis and screening for inherited metabolic diseases. The broad-spectrum of diseases covered, specificity, ease of sample preparation, and high throughput provided by the MS/MS technology has led to the development of multi-disorder newborn screening programs in many countries for amino acid disorders, organic acidurias, and fatty acid oxidation defects. The application of MS/MS in selective screening has revolutionized the field and made a major impact on the detection of certain disease classes such as the fatty acid oxidation defects. New specific and rapid tandem mass spectrometry (MS/MS) and high performance liquid chromatography–MS/MS methods are supplementing or replacing some of the classical gas chromatography– MS/MS methods for a multitude of metabolites and disorders. In the near future, we should expect the emergence of new promising methods for diagnosing not only individual nosologic forms, but also entire groups of inherited metabolic diseases.

Measurements of plasma metanephrines by immunoassay vs liquid chromatography with tandem mass spectrometry for diagnosis of pheochromocytoma.

Reports conflict concerning measurements of plasma metanephrines (MNs) for diagnosis of pheochromocytomas/paragangliomas (PPGLs) by immunoassays compared with other methods. We aimed to compare the performance of a commercially available enzyme-linked immunoassay (EIA) kit with liquid chromatography-tandem mass spectrometric (LC-MS/MS) measurements of MNs to diagnose PPGLs. In a substudy of a prospective, multicenter trial to study the biochemical profiles of monoamine-producing tumors, we included 341 patients (174 males and 167 females) with suspected PPGLs (median age 54 years), of whom 54 had confirmed PPGLs. Plasma MNs were measured by EIA and LC-MS/MS, each in a specialized laboratory. Plasma normetanephrine (NMN) and MN were measured 60 and 39% lower by EIA than by LC-MS/MS. Using upper cut-offs stipulated for the EIA, diagnostic sensitivity was only 74.1% at a specificity of 99.3%. In contrast, use of similar cut-offs for MN and overall lower age-adjusted cut-offs for NMN measured by LC-MS/MS returned a diagnostic sensitivity and specificity of 98.1 and 99.7%. Areas under receiver-operating characteristic curves, nevertheless, indicated comparable diagnostic performance of the EIA (0.993) and LC-MS/MS (0.985). Diagnostic sensitivity for the EIA increased to 96.2% with a minimal loss in specificity (95.1%) following use of cut-offs for the EIA adapted to correct for the negative bias. The EIA underestimates plasma MNs and diagnostic sensitivity is poor using commonly stipulated cut-offs, resulting in a high risk for missing patients with PPGLs. Correction of this shortcoming can be achieved by appropriately determined cut-offs resulting in comparable diagnostic performance of EIA and LC-MS/MS assays.

The role of salivary cortisol measured by liquid chromatography–tandem mass spectrometry in the diagnosis of subclinical hypercortisolism

The use of late-night salivary cortisol (LNSalC) for diagnosing subclinical hypercortisolism (SH) is debated. No data are available regarding the role of LNSalC as measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in SH diagnosis. The aim of this study was to evaluate the diagnostic accuracy of LNSalC measured by LC-MS/MS in SH. Cross-sectional prospective study of outpatients. In 70 consecutive patients with adrenal incidentalomas (AI), without signs and symptoms of hypercortisolism, we diagnosed SH in the presence of at least two of the following: cortisol after 1 mg overnight dexamethasone suppression test (1 mg DST) >83 nmol/l, 24-h urinary free cortisol (UFC) >193 nmol/24 h, and morning ACTH <2.2 pmol/l. The LNSalC levels by LC-MS/MS at 2300 h (normal values <2.8 nmol/l) and the presence of hypertension, type 2 diabetes mellitus (T2DM), and osteoporosis (OP) were assessed. The increased LNSalC levels (>2.8 nmol/l) had an 83.3% specificity (SP) and a 31.3% sensitivity (SN) for predicting the biochemical diagnosis of SH. The increased LNSalC had an 85.2% SP and a 55.6% SN for predicting the presence of hypertension, T2DM, and OP, while the combination of LNSalC >1.4 nmol/l (cutoff with 100% SN) plus 1 mg DST >50 nmol/l had an 88.9% SN and an 85.2% SP (similar to SH criterion at enrollment). In AI patients, LNSalC measured by LC-MS/MS appears to be useful in combination with 1 mg DST for diagnosing SH, while it is not useful as a single criterion.