Pyroglutamate (5-oxoproline) measured with hydrophilic interaction chromatography (HILIC) tandem mass spectrometry in acutely ill patients

• Published in: Clinica chimica acta 2017-03, Vol.466, p.72-77
• Main Authors: Pretorius, Carel J., Reade, Michael C., Warnholtz, Chris, McWhinney, Brett, Phua, Meng Mei, Lipman, Jeffrey, Ungerer, Jacobus P.J.
• Format: Article
• Language: English
• Subjects: Acidosis - blood; Acidosis - diagnosis; Acute Disease; Anion gap; Chromatography, Liquid - methods; Cohort Studies; Humans; Hydrophilic interaction chromatography; Hydrophobic and Hydrophilic Interactions; Limit of Detection; Mass spectrometry; Metabolic acidosis; Oxoproline; Pyroglutamate; Pyrrolidonecarboxylic Acid - blood; Reference Standards; Severity of Illness Index; Tandem Mass Spectrometry - methods; Tandem Mass Spectrometry - standards
• ISSN: 0009-8981; 1873-3492
• DOI: 10.1016/j.cca.2017.01.012

Pyroglutamic acid (PGA) is challenging to quantify in plasma and is a rare cause of metabolic acidosis that is associated with inherited disorders or acquired after exposure to drugs. We developed a hydrophilic interaction liquid chromatography tandem mass spectrometry method with a short analysis time. We established a reference interval and then measured PGA in acutely ill patients to investigate associations with clinical, pharmaceutical and laboratory parameters. The assay limit of the blank was 0.14μmol/L and was linear to 5000μmol/L with good precision. In-source formation of PGA from glutamate and glutamine was avoided by chromatographic separation. The PGA in controls had a reference interval of 22.6 to 47.8μmol/L. The median PGA concentration in acutely ill patients was similar (P=0.21), but 18 individuals were above the reference interval with concentrations up to 250μmol/L. We detected an association between PGA concentration and antibiotic and acetaminophen administration as well as renal impairment and severity of illness. Elevations of PGA in this unselected cohort were small compared to those reported in patients with pyroglutamic acidosis. The method is suitable for routine clinical use. We confirmed several expected associations with PGA in an acutely ill population. •Pyroglutamic acid (PGA) is challenging to quantify in plasma and is a rare cause of metabolic acidosis.•We developed a HILIC mass spectrometry method, established a PGA reference interval (22.6 to 47.8μmol/L) and investigated an acutely ill patient cohort. The measuring range was 0.14μmol/L to 5000μmol/L with good precision.•The median PGA were similar in ill patients, but 16.5% had elevated PGA up to 250μmol/L.•Univariate and multivariate analysis indicated an association between raised PGA concentration and antibiotic and acetaminophen administration, renal impairment and severity of illness. Elevations were small compared to those reported in overt acidosis.