Intra-individual Biological Variation Research Articles

Clinical utility of personalized reference intervals for CEA in the early detection of oncologic disease.

Personalized reference intervals (prRI) have been proposed as a diagnostic tool for assessing measurands with high individuality. Here, we evaluate clinical performance of prRI using carcinoembryonic antigen (CEA) for cancer detection and compare it with that of reference change values (RCV) and other criteria recommended by clinical guidelines (e.g. 25 % of change between consecutive CEA results (RV25) and the cut-off point of 5 μg/L (CP5)). Clinical and analytical data from 2,638 patients collected over 19 years were retrospectively evaluated. A total 15,485 CEA results were studied. For each patient, we calculated prRI and RCV using computer algorithms based on the combination of different strategies to assess the number of CEA results needed, consideration of one or two limits of reference interval and the intraindividual biological variation estimate (CVI) used: (a)publicly available (CVI-EU), (b) CVI calculated using an indirect method (CVI-NOO) and (c) within-person BV (CVP). For each new result identified falling outside the prRI, exceeding the RCV interval, RV25 or CP5, we searched for records identifying the presence of tumour at 3 and 12months after the test. The sensitivity, specificity and predictive power of each strategy were calculated. PrRI approaches derived using CVI-EU, and both limits of reference interval achieve the best sensitivity (87.5 %) and NPV (99.3 %) at 3 and 12months of all evaluated criteria. Only 3 results per patients are enough to calculate prRIs that reach this diagnostic performance. PrRI approaches could be an effective tool to rule out new oncological findings during the active surveillance of patients.

Variations in tumor growth, intra-individual biological variability, and the interpretation of changes.

The identification of changes in tumor markers (TMs) in cancer patients that indicate response to treatment, stabilization or disease progression is a challenge for laboratory medicine. Several approaches have been proposed: assessing percentage increases, applying discriminant values, and estimating half-life (t1/2) or doubling time (DT). In all of them it is assumed that the TM is a surrogate of the variation in tumor size. In general this variation is time-dependent, but this is not the case of intraindividual biological variability (CVi), which can range from 6 % in CA15-3 to 22 % in CA125. When decisions are made on the basis of DT or t1/2, these values can be affected by the CVi; if it is very large, the growth rate very slow and the period of time between determinations very short, the result obtained for DT may be due mainly to the CVi. The aim of this study is to establish the relationship between the CVi and temporal variables. We related equations for calculating DT and t1/2 to the reference change values in tumor markers. The application of the formula obtained allows the calculation of the optimal time between measurements to ensure that the influence of the CVi is minimal in different types of tumors and different scenarios. Intraindividual variation affects the calculation of DT and t1/2. It is necessary to establish the minimum time between two measurements to ensure that the CVi does not affect their calculation or lead to misinterpretation.

Abstract 12103: Intraindividual Variability in Serial Lipoprotein(a) Concentration Among Placebo-Treated Patients in the OCEAN(a)-DOSE Trial

Background: It has been suggested that lipoprotein(a) [Lp(a)] concentrations are stable over time and need to be measured only once in a lifetime. However, data assessing intraindividual variability in Lp(a) concentration are limited. Methods: OCEAN(a)-DOSE, a phase 2, randomized trial of the Lp(a)-lowering siRNA therapy olpasiran, enrolled 281 patients with atherosclerotic cardiovascular disease (ASCVD) and Lp(a) >150 nmol/L. Analyses were conducted in patients randomized to placebo (n=53) with serial Lp(a) values every 4 to 12 weeks through 72 weeks (820 total serum samples). Intra-individual biological variation (CV i ) was calculated as standard deviation of Lp(a) values over time in an individual divided by the mean of those values. All Lp(a) values were measured using the Roche Tina-quant Gen.2 assay reporting in molarity (assay CV 0.7% at 105 nmol/L). Results: Median baseline Lp(a) in the placebo arm was 246 nmol/L (IQR 200-343); median number of Lp(a) measurements per subject was 16. Whereas the overall Lp(a) concentration remained similar across visits (standard deviation 2.6% of the mean), the intra-individual variation over time (CV i ) was 10% [SD 3.9%] of the mean. This variation remained similar across a range of mean Lp(a) values for each participant (Figure). The absolute observed differences in the placebo arm over time across all visits was 22 ± 21 nmol/L (mean ± SD), with a maximum absolute difference of up to 135 nmol/L from an individual patient’s mean. When evaluating outliers, 23% of patients experienced an upward or downward > or equal to 25% change from their individual mean on at least 1 visit, and 51% experienced an upward or downward > or equal to 50 nmol/L change on at least 1 visit. Conclusion: Among patients with ASCVD and elevated baseline Lp(a) concentration, there was notable intra-individual variability in Lp(a) concentration over 72 weeks of follow-up. These findings suggest that Lp(a) may need to be measured more than once in a lifetime.

Verifying measurements on Siemens Atellica® instruments using clinically acceptable analytical performance specifications

Measurements on clinical chemistry analysers must be verified to demonstrate applicability to their intended clinical use. We verified the performance of measurements on the Siemens Atellica® Solution chemistry analysers against the clinically acceptable analytical performance specifications, CAAPS, including the component of intra-individual biological variation, CVI . The relative standard uncertainty of measurement, i.e. analytical variation, CVA , was estimated for six example measurands, haemoglobin A1c in whole blood (B-HbA1c), albumin in urine (U-Alb), and the following measurands in plasma: sodium (P-Na), pancreatic amylase (P-AmylP), low-density lipoprotein cholesterol (P-LDL-C), and creatinine (P-Crea). Experimental CVA was calculated from single-instrument imprecision using control samples, variation between measurements on parallel instruments, and estimation of bias with pooled patient specimens. Each obtained CVA was compared with previously developed CAAPS. The calculated CVA was 1.4% for B-HbA1c (CAAPS 1.9% for single diagnostic testing, CAAPS 2.0% for monitoring after duplicate tests; IFCC units), 10.9% for U-Alb (CAAPS 44.9%), 1.2% for P-Na (CAAPS 0.6%, after triplicate testing 1.5%), 8.2% for P-AmylP (CAAPS 22.9%). The CVA was 4.9% for P-LDL-C (CAAPS for cardiovascular risk stratification 4.9% after four replicates), and 4.2% for P-Crea (CAAPS 8.0%). Three of the six measurands fulfilled the estimated clinical need. Results from P-Na measurements indicate a general need for improving the P-Na assays for emergency patients. It is necessary to consider CVI when creating diagnostic targets for laboratory tests, as emphasised by the CAAPS estimates of B-HbA1c and P-LDL-C.

Elevated insulin-like growth factor-1 in patients without clinical evidence of acromegaly.

To 1) identify the frequency of IGF-1 elevation in a cohort of patients without clinically suspected GH excess, in a state-based reference laboratory over a 24-month period, and 2) to examine potential differences in comorbidities and relevant medications between people with an elevated IGF-1 compared to a matched control group. All IGF-1 measurements at Pathology Queensland between 1/12/2018 - 1/12/2020 were identified. The medical records of those with IGF-1 ≥1.1x the upper limit of the reference range were appraised to determine: 1) documentation of acromegalic features, 2) relevant comorbidities and medication use, and 3) further investigations to exclude pathological GH excess. There were 2759 IGF-1 samples measured in 1963 people ≥18 years, over the specified period. Of these, 204 had IGF-1 ≥1.1x the upper limit of the age-matched reference range; 102 cases (61M, 41F) met inclusion criteria, and were matched to 102 controls with a normal IGF-1 based on age, sex, gonadal status and pituitary anatomy on MRI. There were significant differences in the frequency of dopamine agonist use (19/102 cases vs 6/102 controls, OR=3.66, 95%CI: 1.45-9.29, P=0.009) and chronic kidney disease (CKD) (14/102 cases vs 4/102 controls, OR = 3.90, 95%CI: 1.28-11.14, P=0.024). Out of 1963 patients having IGF-1 measured, 102 (5.2%) had an elevated IGF-1 where there was no known acromegaly, GH replacement or endogenous glucocorticoid excess. Intra-individual biological variability, assay imprecision and physiological factors are known contributors to falsely elevated IGF-1, dopamine agonist therapy and CKD should also be considered. This article is protected by copyright. All rights reserved.

Precision nutrition: approach for understanding intra-individual biological variation

Precision nutrition: approach for understanding intra-individual biological variation

Estimation of inter-laboratory reference change values from external quality assessment data.

IntroductionIt is common for patients to switch between several healthcare providers. In this context, the long-term follow-up of medical conditions based on laboratory test results obtained from different laboratories is a challenge. The measurement uncertainty in an inter-laboratory context should also be considered in data mining research based on routine results from randomly selected laboratories. As a proof-of-concept study, we aimed at estimating the inter-laboratory reference change value (IL-RCV) for exemplary analytes from publicly available data on external quality assessment (EQA) and biological variation.Materials and methodsExternal quality assessment data of the Reference Institute for Bioanalytics (RfB, Bonn, Germany) for serum creatinine, calcium, aldosterone, PSA, and of whole blood HbA1c from campaigns sent out in 2019 were analysed. The median CVs of all EQA participants were calculated based on 8 samples from 4 EQA campaigns per analyte. Using intra-individual biological variation data from the EFLM database, positive and negative IL-RCV were estimated with a formula based on log transformation under the assumption that the analytes under examination have a skewed distribution.ResultsWe estimated IL-RCVs for all exemplary analytes, ranging from 13.3% to 203% for the positive IL-RCV and - 11.8% to - 67.0% for the negative IL-RCV (serum calcium - serum aldosterone), respectively.ConclusionExternal quality assessment data together with data on the biological variation – both freely available – allow the estimation of inter-laboratory RCVs. These differ substantially between different analytes and can help to assess the boundaries of interoperability in laboratory medicine.

POS-051 IMPACT OF USING REFERENCE CHANGE VALUE OF SERUM CREATININE IN THE DIAGNOSIS, STAGING AND OUTCOME OF ACUTE KIDNEY INJURY IN CRITICALLY ILL CHILDREN:AN INTERIM ANALYSIS

The initial diagnosis and staging of AKI by KDIGO creatinine criteria is based on small increase of serum creatinine (sCr) from baseline.To estimate if a change in sCr represents a true change in child, the intrinsic or intra-individual biological variation (CVi) of sCr must be taken into account.Objective :To estimate the reference change value (CVi) of serum creatinine in Indian children. To compare the burden and severity of AKI in critically ill children according to “paediatric reference change value optimized for AKI in children” (pROCK) and KDIGO creatinine criteria (0.3 mg/dL or 50% increase from baseline), and their association with morbidity and risk of in-hospital mortality

Implementation of metrological traceability in laboratory medicine: where we are and what is missing.

Background The Joint Committee on Traceability in Laboratory Medicine (JCTLM) has recently created the Task Force on Reference Measurement System Implementation (TF-RMSI) for providing guidance on traceability implementation to in vitro diagnostics (IVD) manufacturers. Using serum creatinine (sCr) as an example, a preliminary exercise was carried out by checking what type of information is available in the JCTLM database and comparing this against derived analytical performance specifications (APS) for measurement uncertainty (MU) of sCr. Content APS for standard MU of sCr measurements were established as a fraction (≤0.75, minimum quality; ≤0.50, desirable quality; and ≤0.25, optimum quality) of the intra-individual biological variation of the measurand (4.4%). By allowing no more than one third of the total MU budget for patient samples to be derived from higher-order references, two out of the four JCTLM reference materials (RMs) at least allow minimum APS to be achieved for the MU of patient samples. Commutability was explicitly assessed for one of the JCTLM-listed matrixed RMs, which was produced in compliance with ISO 15194:2009 standard, whereas the remaining three RMs were assessed against the ISO 15194:2002 version of the standard, which only required the extent of commutability testing to be reported. Regarding the three listed reference methods, the MU associated with isotopic dilution-mass spectrometry coupled to gas chromatography (ID/GC/MS) and isotopic dilution-mass spectrometry coupled to liquid chromatography (ID/LC/MS) would allow APS to be fulfilled, while the isotope dilution surface-enhanced Raman scattering (ID/SERS) method displays higher MU. Summary The most recently listed RM for sCr in the JCTLM database meets the ISO 15194:2009 requirements with MU that would allow APS to be fulfilled and has had commutability demonstrated for use as a common calibrator in implementing traceability of sCr measurements. Splitting clinical samples with a laboratory performing ID/GC/MS or ID/LC/MS provides an alternative but would also require all components of uncertainty of these materials to be assessed. Outlook Using appropriately derived APS to judge whether reference measurement system components are fit for purpose represents a novel approach. The TF-RMSI is planning to review a greater number of measurands to provide more robust information about the state of the art of available reference measurement systems and their impact on the ability of clinical measurements to meet APS.

Red Blood Cells and Platelets Conventional and Research Parameters: Stability Remarks Before Their Interpretation.

To analyze the stability of red blood cells, platelets, and reticulocytes of the research parameters, in combination with the respective conventional parameters, for each analyte; and to quantify the morphological changes in these analytes, to propose a correction factor for each. Ethylenediaminetetraacetic acid (EDTA) blood specimens from patients were reanalyzed in 2-hour intervals and then, the mean percentage (X¯t%) changes were calculated. To evaluate the stability of the analyzed material, we used different criteria according to within-run and between-batch analytical variation, as well as intraindividual biological variation. Next, the mean deviation percentage of the parameters that undergo time-dependent significant changes was calculated, to obtain a correction factor. Several conventional and research parameters showed significant alterations in the stability at an early time after arrival at the laboratory. Cell variations over time can be quantified and corrected by applying a multiplying factor to the signal obtained in the analyzer.

Technical Considerations and Confounders for Urine CXCL10 Chemokine Measurement.

Background.The urine C-X-C motif chemokine 10 (CXCL10) is a promising screening biomarker for renal allograft rejection. The aim of the study was to investigate important technical and biological aspects as well as potential confounders when measuring urine CXCL10.Methods.We analyzed 595 urine samples from 117 patients, who participated in a randomized controlled trial investigating the clinical utility of urine CXCL10 monitoring for posttransplant management. Urine CXCL10 was measured by an immunoassay using electrochemiluminescence.Results.Intraassay coefficient of variation was 2.5%, and interassay coefficient of variation was 10%. Urine CXCL10 remained stable (ie, <10% degradation) for 8 hours at 25°C or 37°C and for 3 days at 4°C. CXCL10 concentrations [pg/mL] strongly correlated with urine CXCL10/creatinine ratios [ng/mmol] (r2 = 0.98; P < 0.0001). Leucocyturia and active BK-polyomavirus infection are associated with higher CXCL10 concentrations, while allograft function, serum CRP, patient age, proteinuria, urine pH, hematuria, squamous epithelia cell count, and bacteriuria did not correlate with urine CXCL10 concentrations. In 145 paired samples obtained within 1–2 weeks, 80% showed a CXCL10/creatinine ratio change of < ±2 ng/mmol or ±50%, respectively.Conclusions.Urine CXCL10 measurement on the used platform is accurate and robust. Leucocyturia and active BK-polyomavirus infection are major confounders, which can be easily detected but represent important diagnostic “blind spots” when using urine CXCL10 to screen for allograft rejection. The intraindividual biological variability of urine CXCL10 within 1–2 weeks is mostly below ±50%, which is still much higher than the technical variability due to sample handling/processing (<20%).

Serum Levels of Coll2-1, a Specific Biomarker of Cartilage Degradation, Are Not Affected by Sampling Conditions, Circadian Rhythm, and Seasonality

To assess intraindividual biological variability of serum cartilage specific biomarker Coll2-1 and define the best standardized conditions for blood sampling. Blood samples were taken from 116 subjects with knee osteoarthritis (OA) at a single time point (PRODIGE study) and from 15 healthy subjects under various conditions, including fasting condition, sampling time and season, blood treatment, and type of blood collection tube (COVAR study). Type II collagen-specific biomarker Coll2-1 was directly measured in serum using an immunoassay. There was no significant difference on Coll2-1 values between samples collected at any of the 5 sampling times or at any of the sampling days measured. None of the sampling parameters tested had a significant impact on Coll2-1 value (clotting time, clotting temperature and temperature of blood centrifugation, type of tube). On the contrary, differences were found in between subjects and between subjects with knee OA and healthy subjects. Coll2-1 measurement is not affected by sampling specific conditions, circadian rhythm or seasons but was found elevated in subject with knee OA indicating that Coll2-1 serum variation is not linked to the study environment, but to cartilage degradation in OA. Coll2-1 assay is sufficiently robust for use in OA clinical trials.

Longitudinal Intra- and Inter-individual variation in T-cell subsets of HIV-infected and uninfected men participating in the LA Multi-Center AIDS Cohort Study.

To assess the intra-individual and inter-individuals biological variation and the effect of aging on lymphocyte T-cells subsets.We assessed lymphocyte phenotypes (CD3, CD4, and CD8 T-cells) in 89 HIV-1-infected and 88 uninfected white non-Hispanic men every 6 months, to examine the biological variation for those measurements, and the average change in lymphocyte phenotype over 34 years.The markers showed significant intra-individuality in HIV-infected and uninfected individuals with index of individuality of <1.4. No mean changes were seen over the 34 years, with the exception of percentage CD4T-cells in HIV-uninfected individuals.In the pre-HAART era, HIV-infected individuals experienced an increase in mean absolute CD3 T-cell numbers (11.21 cells/μL, P = 0.02) and absolute CD8 T-cell numbers (34.57 cell/μl, P < .001), and in the percentage of CD8 T-cells (1.45%, P < .001) per year and a significant decrease in mean absolute CD4 T-cell numbers (23.68 cells/μl, P < .001) and in the percentage of CD4 T-cells (1.49%, P < .001) per year.In the post-HAART era, no changes in mean levels were observed in absolute CD3 T-cell count (P = .15) or percentage (P = .99). Significant decreases were seen in mean count (8.56 cells/μl, P < .001) and percentage (0.59%, P < .001) of CD8 T-cells, and increases in mean absolute count (10.72 cells/μl, P < .001) and percentage (0.47%, P < .001) of CD4 T-cells.With the exception of CD4 (%), no average changes per year were seen in lymphocyte phenotype of HIV-uninfected men. The results of coefficients of variation of intra and inter-individuals of this study can be useful for HIV-1 infection monitoring and in addition the observation could be a useful guide for intra- and inter-individual coefficient variations, and establishing quality goal studies of different blood biomarkers in healthy and other diseases.

Intra-individual variation of circulating tumour DNA in lung cancer patients.

Circulating tumour DNA (ctDNA) has been increasingly incorporated into the treatment of cancer patients. ctDNA is generally accepted as a powerful diagnostic tool, whereas the utility of ctDNA to monitor disease activity needs to be fully validated. Central to this challenge is the question of whether changes in longitudinal ctDNA measurements reflect disease activity or merely biological variation. Thus, the aim of this study was to explore the intra‐individual biological variation of ctDNA in lung cancer patients. We identified tumour‐specific mutations using next‐generation sequencing. Day‐to‐day and hour‐to‐hour variations in plasma concentrations of the mutant allele and wild‐type cell‐free DNA (cfDNA) were determined using digital PCR. The levels of the mutant alleles varied by as much as 53% from day to day and 27% from hour to hour. cfDNA varied up to 19% from day to day and up to 56% from hour to hour, as determined using digital PCR. Variations were independent of the concentration. Both mutant allele concentrations and wild‐type cfDNA concentrations showed considerable intra‐individual variation in lung cancer patients with nonprogressive disease. This pronounced biological variation of the circulating DNA should be investigated further to determine whether ctDNA can be used for monitoring cancer activity.

Presepsin: co je nutné vědět pro korektní interpretaci

Presepsin (soluble CD14 subtype) is a new biomarker of infection and sepsis. Correct interpretation is based on the knowledge of analytical reliability, biological variation, decision limits, and diagnostic effectivity.The aim of the study was to verify analytical precision of presepsin measurements, to assess biological variation in healthy subjects, to verify reference and decision limits, to assess diagnostic effectivity, and to compare data with commonly used septic biomarkers - procalcitonin (PCT), CRP and interleukin 6 (IL6).Analyti-cal precision (repeatability and intermediate precision) was estimated by repeated measurements of commercial control materials. Biological variation was evaluated in a group of 20 healthy volunteers in a 7-week experi-ment. Reference ranges were extracted from the literature and compared with data from healthy subjects.Precisions of presepsin measurements were 2.0-4.0 % (&#8220;within-run&#8221;) and 6.1-9.5 % (&#8220;between-run&#8221;). Intraindividual biological variation of presepsin was 22.3 %, interindividual variation 20.8 %. Index of individuality was 1.07, reference change value (RCV - critical difference) was 72 %. Upper reference limit was around 180 ng/l.Ana-lytical quality of presepsin measurement is suitable for clinical use. Biological variation parameters enable the use of reference limits, upper reference limit of presepsin is around 180 ng/l. None of the tested biomarkers has universal cut-off value, multiple biomarkers are needed and repeated measurements are advisable.

Serum anti-Müllerian hormone concentration before and after salpingectomy for ectopic pregnancy.

Does salpingectomy for ectopic pregnancy affect the ovarian reserve measured by changes in pre- and post-operative levels of anti-Müllerian hormone (AMH)? This is a prospective observational multicentre study of 64 women treated with salpingectomy for an ectopic pregnancy. AMH was measured in serum samples collected at admission before salpingectomy and at follow-up (median time to follow-up [interquartile range] was 3 [3-4] months). Changes in serum AMH levels were investigated using Wilcoxon signed-rank test and the relationship between changes in AMH and age, time to follow-up, and pre-operative serum AMH level was investigated using linear regression analysis. The biological variation of AMH was also calculated. Serum AMH levels did not differ significantly before and after salpingectomy (median ∆AMH [follow-up value minus admission value] 0.40 pmol/l, interquartile range -2.0 to 4.0 pmol/l). ΔAMH was independent of age, time to follow-up and pre-operative serum AMH level. The intra-individual biological variation for AMH ranged from 12.1% to 26.3%, depending on time between the two samples. This is the first paired study to investigate serum AMH values before and after salpingectomy in an unselected population of women presenting with an ectopic pregnancy, including both patients who conceived naturally and following fertility treatment. It was found that salpingectomy for ectopic pregnancy had no short-term effect on serum AMH levels, and changes in AMH levels were independent of age, time to follow-up, and pre-operative serum AMH level. Furthermore, the study demonstrated a 6-month biological variation of AMH of less than 30%.

Stability of leukocyte research parameters over time on the Sysmex XN: How to quantify the changes in cell morphology.

Research parameters of the Sysmex XN-series provide information about the cell morphology. The aim is to quantify time-dependent changes of conventional and research parameters and propose correction factors to be applied to the parameters, which revealed significant changes. 284 EDTA blood samples were processed from 0hours-12hours and the mean percentage change ( %) of the leukocyte parameters was calculated. Stability was evaluated according to three criteria: metrology criteria according to the between-batch analytical variation, metrology criteria according to within-run analytical variation, by which % could not exceed the Minimum Significant Change (MSC=[±1.65*CV%]) and Biological criteria based on intraindividual biological variation, by which % could not exceed the Desirable Significant Change (DSC=[±0.5*CVD %]). Mean deviation percentage of the parameters, which suffer significant changes was calculated and a multiplying factor was obtained to correct the signal deviation. Stability of abnormal leukocyte flags was also evaluated. Most of the cell count parameters are considered stable according to MSC and DSC. However, several research parameters of neutrophils and lymphocytes show alterations in stability after 4hours, even when their respective cell count parameters are stable. Morphological variations of neutrophils and lymphocytes can be quantified. This data can be used to correct the deviation in samples that cannot be analyzed before 4hours.

Intra-individual biological variation in sweat chloride concentrations in CF, CFTR dysfunction, and healthy pediatric subjects.

The sweat test is one of the main diagnostic tools used in newborn screening programs and as a confirmatory test, in case of suspect of Cystic Fibrosis (CF). Since sweat chloride (Cl) concentration is also considered an appropriate parameter to explore the efficacy of CFTR modulators in clinical trials, it is crucial to evaluate the biological variability of this test in healthy and pathological conditions. The aim of this pilot study was to determine the intra-individual biological variability of sweat Cl, both in healthy individuals and CF patients and to assess its correlation with diet, season, and menstrual cycle. Thirty-five out of 36 selected subjects (6-18 years) were enrolled by 2 CF care centers and assigned to 3 cohorts: CF, CFTR-related disorder (CFTR-RD) and healthy volunteers. Each participant was subjected to eight sweat tests in different conditions and time of the year. Data were analyzed using linear mixed effects models for repeated measures, taking also into account intra-individual correlations. We observed a high intra-individual variability of sweat Cl, with the lowest mean CV% values among CF patients (20.21 in CF, 29.74 in CFTR-RD, and 31.15 in healthy subjects). Gender and diet had no influence on sweat Cl variability, nor had pubertal age and menstrual phase. Results of this pilot study confirmed that sweat Cl variability is high in CF patients, although non-CF individuals displayed even higher mean CV% values. Season significantly influenced sweat test values only in CF patients, likely due to changes in their hydration status.

Metabolomics in Human Acute-Exercise Trials: Study Design and Preparation.

Metabolomics can be of great value in the study of exercise metabolism. However, because of the high intraindividual and interindividual biological variability of the human metabolome, special considerations should be taken into account when designing an acute-exercise metabolomic study. To study different exercise parameters, e.g., different exercise modes, intensities, etc., a crossover study design, where each participant acts as their own control, is preferable to a parallel design, one involving different groups of participants. Moreover, the study should include a no exercise, control trial. Before each trial, participants should follow carefully designed preparatory steps to control for possible confounding factors, i.e., maintain repeatable and constant conditions for all individual trials of the study to minimize variation due to factors other than the one(s) being studied. This chapter focuses on the design of human metabolomic studies, where the intervention is an acute metabolic challenge, such as an exercise bout or a test meal, and presents some basic steps for screening potential participants, performing preliminary tests, preparing for the trial day, and performing the trial.

Biological variation of serum neuron-specific enolase and carbohydrate antigen 724 tumor markers.

The aim of our study was to assess two tumor markers, carbohydrate antigen 724 (CA724) and neuron-specific enolase (NSE), in 20 healthy individuals. Then, we determined their average intra- and inter-individual biological variations (CVI and CVG ). Blood samples were taken at weekly intervals for five weeks from 20 healthy subjects through a detailed questionnaire and physical examination. These samples were stored at -80°C and analyzed in a single run in duplicate. We calculated the biological variations, the reference change value (RCV), and the index of individuality (II) for the two tumor markers. The intra-individual and inter-individual biological variations were 50.3% and 103.4% for CA724, and 10.1% and 12.0% for NSE, respectively. The II values for CA724 and NSE were 0.48 and 0.85, respectively. We determined the biological variations and indices of individuality for CA724 and NSE among 20 healthy subjects. These results will improve clinical applications of the markers.