Changes In Serial Results Research Articles

Assessment of Biological Variation and Analytical Imprecision of CA 125, CEA, and TPA in Relation to Monitoring of Ovarian Cancer

Objectives. Changes in serial tumor marker results during monitoring of patients with ovarian cancer are due not only to deterioration or amelioration of the patient's condition, but also to preanalytical sources of variation (CPP), total random analytical error, and within-subject normal biological variation. The aim of the study was to assess (i) the analytical imprecision (CVA) and the average inherent intra- and interindividual biological variation (CVTI and CVG, respectively) for CA 125, CEA, and TPA in a group of healthy women; (ii) the significance of changes in serial results of each marker; and (iii) the index of individuality.Methods. The study group consisted of 31 healthy women. Sixteen blood samples from each subject were collected in four series over a period of approximately 1 year. Data analysis was based on ANOVA. The index of individuality was calculated as ((CV2A + CV2TI)/CV2G)1/2 and the critical difference for a change between two consecutive concentrations as √2xZx(CV2P + CV2A + CV2TI)1/2 (Z = 1.65 for unidirectional and 1.96 for bidirectional changes, P ≤ 0.05).Results. The averages of CVTI and CVG were 35.5 and 70.6% for CA 125, 13.9 and 58.3% for CEA, and 31.4 and 62.5% for TPA, respectively. The indices of individuality were 0.5 for CA 125, 0.3 for CEA, and 0.5 for TPA. The critical differences of CA 125, CEA, and TPA were 84.6, 37.6, and 76.3%, respectively (Z = 1.65). There were no significant differences in CA 125, CEA, and TPA concentrations between smokers and nonsmokers or in CA 125 and CEA concentrations between pre- and postmenopausal women. Postmenopausal women had higher TPA concentrations than premenopausal (P = 0.015).Conclusion. CVA and CVTI contribute considerably to the variation in serial results and should, therefore, be included in the criteria for serum tumor marker assessment during monitoring of patients with ovarian cancer.

Biological Variation of Free and Total Carnitine in Serum of Healthy Subjects

Determination of carnitine (l-β-hydroxy-γ-trimethylaminobutyric acid) in biological samples plays an important role in the diagnosis of diseases with carnitine deficiency (1). In the past few years, and also in this Journal, several spectrophotometric methods for assaying carnitine in serum have been described (2)(3)(4)(5)(6). To our knowledge, however, no data have been published on the biological variation of this serum analyte. For any new test, data on the biological variation generated from the healthy population may be used (a) in setting desirable performance standards or analytical goals, (b) in assessing the utility of conventional population-based reference intervals, and (c) in critically evaluating the significance of changes in serial results from an individual (7). To investigate the analytical and biological variation of free and total carnitine, as well as of the acyl/free carnitine ratio, we collected blood samples once a week for 4 weeks from each of 14 healthy subjects (7 men and 7 nonpregnant women, ages 21–23 years), students of Mathias Belius University. The subjects agreed to maintain current dietary habits, body weight, and exercise program (if any) for the duration of the study. The criteria of the hospital Ethics Committee were respected in this experiment. To minimize sources of preanalytical variation, venous blood specimens were drawn between 0800 and 0900 h after ∼12 h of fasting. The subjects …

Model for Establishing Biological Variation in Nonhealthy Situations: Renal Posttransplantation Data

Renal transplantation has come to be accepted as standard treatment for patients with terminal kidney failure. Because the physiological state of the renal transplant recipient is unstable, he or she is monitored with a well-defined protocol that is strictly followed by clinicians. Renal dysfunction is a common complication due to various problems, especially drug toxicity, and rejection is an ever-present danger (1). To detect episodes of rejection, clinicians use empirical criteria derived from experience that is mainly based on changes in creatinine concentrations. Posttransplantation monitoring, which includes frequent analysis of a number of constituents, generates large amounts of data. With this information, finding objective, early indicators that predict trends toward complications before the patient’s condition is seriously compromised would be beneficial, so that preventive actions could be taken. Data from biological variation (BV), the normal fluctuation around the homeostatic set point, has been used to evaluate the significance of changes in serial results (2). Therefore, it can provide clinicians with an indication of future patient status: A change between two consecutive observations higher than the established variation around the homeostatic set point could signal the beginning of a complication. However, the components of BV, sensitive and specific enough to characterize a “certain state of health” from the start of crisis, can be investigated only when a stable situation that denotes equilibrium has been demonstrated in the specific pathology. The aims of this work were to delineate the stable period after renal transplantation for six serum analytes expected to reflect instability/rejection, and to calculate within- and between-subject BV, indices of individuality (II), and critical differences (CDs) between serial results and compare outcome with published data in healthy subjects to determine whether BV data can predict crises in this population. We studied 19 patients (12 men and 7 women), 19 to 64 …

Biological Variation of Superoxide Dismutase in Erythrocytes and Glutathione Peroxidase in Whole Blood,

Oxidative stress resulting from increased free-radical production and (or) defects in antioxidant defenses is implicated in the pathogenesis of several diseases (1). Biological effects of these highly reactive compounds are controlled in vivo by a wide spectrum of antioxidant mechanisms. Among these, the enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX) act as endogenous antioxidants (2). Introducing SOD and GPX measurements in laboratory medicine application requires identification of the biological sources of variation for: assessing the desired performance characteristics of a test, deriving the utility of the conventional population-based reference interval, and defining significant differences that imply changes in serial results from an individual (3). Our study was designed to estimate biological variation components of SOD in erythrocytes and GPX in whole blood to examine the role of these enzymes in the diagnosis, screening, and monitoring of patients. Eighteen healthy individuals (8 men and 10 women) between 24 and 48 years of age were included in the study. They agreed to maintain uniform daily habits during the study. Venous blood samples were collected into lithium heparinized tubes once a week, between 0800 and 0900 h, for 5 consecutive weeks. Specimens were drawn from the volunteers after 20 min in a sitting position. Owing to the short time stability of the samples, their analyses were performed on the day of collection. Analytical procedures: SOD activity in erythrocytes was measured by the rate of inhibition of 2-(4-iodophenyl)-3-(4-nitrophenol)-5-phenyltetrazolium chloride (INT) reduction (Ransod SD 125, Randox Lab.) and expressed in U/g of hemoglobin (Hb). …

Biological Variation in Protein C, Protein S and Antithrombin Concentrations in Plasma of Healthy Subjects

The analytical, intra- and inter-individual components of biological variation were estimated for protein C, protein S and antithrombin over a period of 6 weeks in a cohort of 17 apparently healthy subjects. Expressed as percentage activity (protein C and antithrombin) as a percentage concentration in normal human plasma (protein S), the mean values for men and women show no significant differences (p > 0.05) for any of the analytes studied. Calculated analytical goals (CV, %) for precision required for optimal patient care are: protein C, 2.9; protein S, 2.9 and antithrombin 2.7. A single numerical index, called "index of fiduciality", was also calculated to demonstrate that the analytical performance of our method was satisfactory. The generally applicable differences (% activity or % concentration) required for two results to be significantly different (p < or = 0.05) were calculated as: protein C, 17; protein S, 16 and antithrombin, 16. The usefulness of critical differences as guidelines for the interpretation of changes in serial results was investigated using an "index of heterogeneity" of intra-individual variation. The marked degree of individuality demonstrated for all the quantities indicates that, if conventional population-based ranges are used uncritically, major changes in analyte concentration may not be correctly identified for some patients, because observed values continue to lie within the reference range. The utility of conventional population-based reference intervals was determined by calculating a single numerical index, called "index of individuality". For protein C, protein S and antithrombin we found that five of a patient's specimens are required to achieve a 95% chance that the mean is within +/- 5% of the true value.

Biological variability of superoxide dismutase and glutathione peroxidase in blood.

The enzymatic antioxidant defences of mammalian cells include copper-zinc superoxide dismutase (SOD)(Cu Zn-SOD; EC 1.15.1.1) which catalyses the dismutation of superoxide anions (O2(.-)) to hydrogen peroxide(H(2), O(2))and a seleno-dependent glutathione peroxidase (GSH-px) (GSH-px; EC 1.11.1.9) which catalyses the degradation of H(2)O(2) to H(2)O and O(2). The measurement of these enzyme activities is often used as a possible biological index of oxidative stress in various clinical conditions. Complete understanding of such information requires knowledge of the random biological fluctuation of the enzyme activity which occurs in each individual. In the present investigation we examined this normal variability in 12 healthy volunteers (four women and eight men) aged 23-45 years, over 6 months. The intra-individual coefficients of variation (estimated using analysis of variance techniques) were 15% (SOD) and 13% (GSH-px). The analytical goal for imprecision was achieved for both enzymes, i.e. it was less than one half of the measured intra-individual variation. Both enzymes showed marked individuality, indicating that an individual's reference values are more useful than population-based data. The critical difference required for significant changes in serial results is 45% for SOD and 40% for GSH-px.

Biological variation of ascorbic acid and α-tocopherol.

Accumulating evidence that free radicals may contribute to various diseases, has sparked epidemiological and experimental studies of the correlation between plasma levels of antioxidant vitamins and risk to develop cancer, ischaemic heart disease and stroke. These studies often do not take into account the random biological fluctuation of the antioxidant concentration, which occurs in each individual. The weekly and monthly variability of the antioxidants ascorbic acid and α-tocopherol was studied in 12 healthy volunteers (4 women and 8 men) aged 23-45 years. Vitamin levels were determined using high performance liquid chromatography. Over 12 weeks the mean plasma concentration of ascorbic acid was 42± 12 μmol/I and of α-tocopherol was 31±3 μmol/I. The intraindividual coefficients of variation (estimated using analysis of variance techniques) were 26% (ascorbic acid) and 12% (α-tocopherol). The analytical goal for imprecision was achieved for both vitamins, i.e. it was less than one-half of the measured intraindividual variation. Both antioxidants showed marked individuality, indicating that an individual's reference values are more useful than population-based data. The critical difference required for significance of changes in serial results is smaller for α-tocopherol (34%) than that for ascorbic acid (72%).

Biological variation of acute phase proteins.

The analytical, within-subject and between-subject components of variation were estimated for serum albumin, transthyretin, alpha 1-acid glycoprotein, alpha 1-antichymotrypsin, haptoglobin, beta 2-microglobulin and C-reactive protein in a cohort of 19 apparently healthy subjects over 20 weeks. Desirable analytical goals based on biological variation should be able to be met except for serum albumin and beta 2-microglobulin for which methodological improvement is warranted. All proteins showed marked individuality which casts doubt on the utility of conventional population-based reference values as interpretative criteria. The critical differences required for significance of changes in serial results differ markedly from protein to protein and the data presented allow generation of objective criteria for monitoring individuals.

Generation and application of data on biological variation in clinical chemistry.

Most clinical chemical analytes vary in a random manner around a homeostatic set point. Replicate analyses of a series of specimens collected from a group of subjects allows estimation of analytical, within and between subject components of variation. The preferred experimental procedures and statistical methods for evaluation of data and analysis of variance are described; a detailed example is provided in the Appendix. The many uses of data on biological variation in clinical chemistry are reviewed, including setting analytical goals, deciding the significance of changes in serial results from an individual, evaluating the utility of conventional population-based reference values in patient management, and other applications.