Reference ranges for the polyethylene glycol (PEG) precipitation activity (%PPA) of eight routine enzyme activities.

Macroenzymes are high-molecular weight forms of enzymes whose presence in human sera can lead to non-pathological, elevated enzyme activities, resulting in further unnecessary clinical evaluation. Precipitation with polyethylene glycol (PEG) is an efficient method for removing macroforms from patient samples and can therefore be used for their identification. Cut-offs (99. Percentiles) for the PEG precipitation activity (%PPA) for eight routine enzyme activities were determined on Abbott's Alinity c, namely: AST (61%), ALT (70%), GGT (41%), LDH (45%), lipase (56%), ALP (17%), CK (36%) and PAMY (45%). Two macroforms (PAMY and CK) were then identified by gel filtration chromatography. We suggest that a %PPA above the enzyme-specific cut-off makes the presence of a macroform possible while a %PPA ≥80%, i.e. markedly above the cut-off, makes it very likely for all enzymes.

Evaluation of Prefrontal γ-Aminobutyric Acid and Glutamate Levels in Individuals With Major Depressive Disorder Using Proton Magnetic Resonance Spectroscopy.

Importance: Major depressive disorder (MDD) is one of the most prevalent illnesses worldwide. Perturbations of the major inhibitory and excitatory neurotransmitters, γ-aminobutyric acid (GABA) and glutamate (Glu), respectively, as well as Glx (Glu or glutamine [Gln]) have been extensively reported in a multitude of brain areas of individuals with depression, but few studies have examined changes in Gln, the metabolic counterpart of synaptic Glu. Objective: To investigate changes in GABA, Glx, Glu, and Gln levels in a voxel in the left dorsolateral prefrontal cortex of participants with no, past, and current MDD using proton magnetic resonance spectroscopy (1H-MRS). Design, Setting, and Participants: This community-based study used a cross-sectional design using 3-T 1H-MRS in participants not taking MDD medication recruited from the community. The sample consisted of 251 healthy controls, 98 participants with a history of past MDD, and 47 participants who met the diagnostic criteria for current MDD. Diagnostic groups were comparable regarding age, education, income, and diet. Data were collected from March 2014 to October 2021, and data were analyzed from October 2021 to June 2022. Main Outcomes and Measures: GABA, Glx, Glu, and Gln concentrations in the left dorsolateral prefrontal cortex. Results: Of 396 included participants, 258 (65.2%) were female, and the mean (SD) age was 25.0 (4.7) years. Compared with healthy controls, those with past MDD and current MDD had lower GABA concentrations (mean [SEM] concentration: healthy controls, 2.70 [0.03] mmol/L; past MDD, 2.49 [0.05] mmol/L; current MDD, 2.54 [0.07] mmol/L; 92 with past MDD vs 236 healthy controls: r = 0.18; P = .002; 44 with current MDD vs 236 healthy controls: r = 0.13; P = .04). Compared with healthy controls, those with past MDD also had lower Glu concentrations (mean [SEM] concentration: healthy controls, 7.52 [0.06] mmol/L; past MDD, 7.23 [0.11] mmol/L; 93 with past MDD vs 234 healthy controls: r = 0.16; P = .01) and higher Gln concentrations (mean [SEM] concentration: healthy controls, 1.63 [0.04] mmol/L; past MDD, 1.84 [0.07] mmol/L; 66 with past MDD 153 healthy controls: r = 0.17; P = .04). Conclusions and Relevance: In a large, mostly medication-free community sample, reduced prefrontal GABA concentrations were associated with past MDD, consistent with histopathologic studies reporting reduced glial cell and GABA cell density in the prefrontal cortex in individuals with depression. Patients with MDD also demonstrated increased Gln levels, indicative of increased synaptic Glu release, adding to previous evidence for the Glu hypothesis of MDD.

Using the hemolysis index of Abbott's Alinity c for the measurement of plasma free hemoglobin in ECMO patients.

OBJECTIVES: Quantitative measurement of plasma free hemoglobin (fHb) concentrations is essential for monitoring pediatric ECMO patients, since hemolysis has a great impact on the patient's clinical outcome. The aim of this study was to validate the hemolysis index (HI) assay on Abbott's Alinity c system as a quantitative method to measure fHb. METHODS: The performance of the HI assay, based on an automated spectrophotometric method recording the absorption at four different wavelength pairs, was evaluated using the 20 × 2 × 2 design according to the CLSI-EP05-A3 guidelines. LLOQ and LLOD were calculated according to CLSI-EP17 guidelines with CVs set to 10% and 20%, respectively. Furthermore, the method was tested for interferences with bilirubin and Intralipid®. RESULTS: Linearity was ensured over an analytical measurement range of 30-7250 mg/L and the calculated LLOQ and LLOD were 80 mg/L and 50 mg/L, respectively. Intra-run and total imprecisions ranged from 0.9-3.4% and 1.0-3.4%, respectively. The HI assay correlated well with the Harboe method (HI (mg/L) = 0.998 * fHb (mg/L) + 28 mg/L, R = 0.998, n = 50) and interference testing showed no impact of bilirubin and Intralipid® up to 709 mg/L and 5580 mg/L, respectively. CONCLUSIONS: The HI assay on Abbott's Alinity c system allows a precise and accurate determination of fHb concentrations with no significant interferences in a simple, rapid and cost-effective way.