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Biomedical subjects

George G Klee

Publications and source records attributed to George G Klee.

At least 19 recordsLinked to original sources
PubMed2006

DHEA in elderly women and DHEA or testosterone in elderly men.

BACKGROUND: Dehydroepiandrosterone (DHEA) and testosterone are widely promoted as antiaging supplements, but the long-term benefits, as compared with potential harm, are unknown. METHODS: We performed a 2-year, placebo-controlled, randomized, double-blind study involving 87 elderly men with low levels of the sulfated form of DHEA and bioavailable testosterone and 57 elderly women with low levels of sulfated DHEA. Among the men, 29 received DHEA, 27 received testosterone, and 31 received placebo. Among the women, 27 received DHEA and 30 received placebo. Outcome measures included physical performance, body composition, bone mineral density (BMD), glucose tolerance, and quality of life. RESULTS: As compared with the change from baseline to 24 months in the placebo group, subjects who received DHEA for 2 years had an increase in plasma levels of sulfated DHEA by a median of 3.4 microg per milliliter (9.2 micromol per liter) in men and by 3.8 microg per milliliter (10.3 micromol per liter) in women. Among men who received testosterone, the level of bioavailable testosterone increased by a median of 30.4 ng per deciliter (1.1 nmol per liter), as compared with the change in the placebo group. A separate analysis of men and women showed no significant effect of DHEA on body-composition measurements. Neither hormone altered the peak volume of oxygen consumed per minute, muscle strength, or insulin sensitivity. Men who received testosterone had a slight increase in fat-free mass, and men in both treatment groups had an increase in BMD at the femoral neck. Women who received DHEA had an increase in BMD at the ultradistal radius. Neither treatment improved the quality of life or had major adverse effects. CONCLUSIONS: Neither DHEA nor low-dose testosterone replacement in elderly people has physiologically relevant beneficial effects on body composition, physical performance, insulin sensitivity, or quality of life. (ClinicalTrials.gov number, NCT00254371 [ClinicalTrials.gov].).

Adult↗
PubMed2006

B-type natriuretic peptide in the assessment of acute lung injury and cardiogenic pulmonary edema.

OBJECTIVE: The role of plasma B-type natriuretic peptide (BNP) in critically ill patients with acute pulmonary edema is controversial. We postulated that a low BNP level would exclude cardiac dysfunction as the principal cause of pulmonary edema and therefore help in the diagnosis of acute lung injury. DESIGN: A retrospective derivation cohort was followed by a prospective validation cohort of consecutive patients with acute pulmonary edema admitted to three intensive care units. BNP was measured within 24 hrs from onset. Critical care experts blinded to BNP results integrated clinical data with the course of disease and response to therapy and served as the reference standard. SETTING: Three intensive care units at the tertiary center. PATIENTS: Consecutive critically ill patients with acute pulmonary edema. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: In a derivation cohort of 84 patients, a BNP threshold of <or=250 pg/mL had a specificity of 87% and sensitivity of 48% for the diagnosis of acute lung injury. High specificity of BNP (90%, likelihood ratio of 3.9) was confirmed in a validation cohort of 120 consecutive patients, 52 (43%) of whom had acute lung injury. Notably, 32% of patients with acute lung injury had concomitant cardiac dysfunction. The median time from the onset of pulmonary edema to BNP testing was 3 hrs. The accuracy of BNP (area under receiver operator curve, 0.71) was comparable with pulmonary artery occlusion pressure (area under receiver operator curve, 0.66) and superior to ejection fraction (area under receiver operator curve, 0.60) in subgroups of patients in whom these tests were performed. The accuracy of BNP improved when patients with renal insufficiency were excluded (area under receiver operator curve, 0.82). CONCLUSION: When measured early after the onset of acute pulmonary edema, a BNP level of <250 pg/mL supports the diagnosis of acute lung injury. The high rate of cardiac and renal dysfunction in critically ill patients limits the discriminative role of BNP. No level of BNP could completely exclude cardiac dysfunction.

Acute Disease↗
PubMed2005

Comparison of pooled fresh frozen serum to proficiency testing material in College of American Pathologists surveys: cortisol and immunoglobulin E.

CONTEXT: The College of American Pathologists (CAP) provides proficiency testing (PT) surveys to laboratories around the world. OBJECTIVES: To compare diagnostic assay methods for serum/plasma cortisol and immunoglobulin (Ig) E in terms of their bias and precision, to determine how well CAP PT specimens simulate human serum, and to reassess proficiency test grading criteria in light of these findings. DESIGN: A participant-blinded, prospective trial. One vial of pooled fresh frozen serum (FFS) and 4 different admixtures of PT material (PTM) were sent to laboratories participating in PT surveys. PARTICIPANTS: Laboratories providing cortisol (>1000) or IgE (>230) results among the subscribers to the CAP surveys, Ligand (General) 2003, set K/KN-A and Chemistry 2003, set C-C. MAIN OUTCOME MEASURES: The main outcome measures were (1) bias among laboratories using the same method (peer groups), defined relative to the median of method means (MedMM); (2) imprecision as measured by the SD and coefficient of variation (CV) about each method mean; and (3) total error across laboratories for the FFS cortisol results, defined as |Bias Relative to Reference Method| + 2 SD. RESULTS: Cortisol method biases, relative to MedMM, ranged from -22% to 9% for the FFS challenge and from -24% to 36% for comparable PTM challenges. The method biases, relative to the reference method, ranged from -3% to 19% for the FFS challenge. The cortisol method CVs ranged from 4.2% to 13.6% for the FFS challenge and from 4.7% to 12.7% for comparable PTM challenges. Total error across laboratories ranged from 1.4 to 6.9 microg/dL (39 to 190 nmol/L) for the FFS challenge. Immunoglobulin E method biases, relative to MedMM, ranged from -8% to 9% for the FFS challenge and from -7% to 5% for comparable PTM challenges. The IgE method CVs ranged from 3.6% to 6.7% for the FFS challenge and from 3.4% to 9.8% for comparable PTM challenges. CONCLUSIONS: The bias for cortisol results was less with FFS than with PTM, but imprecision was comparable. The FFS MedMM was 8.5% higher than the reference value. Fresh frozen serum and PTM bias and imprecision for IgE methods were each less than 10%. Because some of the methods demonstrated greater bias when analyzing PTM than FFS, peer group grading of both these analytes is appropriate.

Clinical Laboratory Techniques↗
PubMed2005

Analytic bias of thyroid function tests: analysis of a College of American Pathologists fresh frozen serum pool by 3900 clinical laboratories.

CONTEXT: In proficiency testing surveys, there are differences in the values reported by users of various analytic methods. Two contributors to this variation are calibrator bias and matrix effects of proficiency testing materials. OBJECTIVES: (1) To quantify the biases of the analytic methods used to measure thyroid-stimulating hormone, thyroxine, triiodothyronine, free thyroxine, and free triiodothyronine levels; (2) to determine if these biases are within allowable limits; and (3) to ascertain if proficiency testing materials correctly identify these biases. DESIGN: A fresh frozen serum specimen was mailed as part of the 2003 College of American Pathologists Ligand and Chemistry surveys. The means and SDs for each analytic method were determined for this sample as well as for a proficiency testing sample from both surveys. In the fresh frozen serum sample, target values for thyroxine and triiodothyronine were determined by isotope dilution/liquid chromatography/tandem mass spectrometry. All other target values in the study were the median of the means obtained for the various analytic methods. MAIN OUTCOME MEASURES: Calibration biases were calculated by comparing the mean of each analytic method with the appropriate target values. These biases were evaluated against limits based on intra- and interindividual biological variation. Matrix effects of proficiency testing materials were assessed by comparing the rank of highest to lowest analytic method means (Spearman rank test) for each analyte. PARTICIPANTS: Approximately 3900 clinical laboratories were enrolled in the College of American Pathologists Chemistry and Ligand surveys. RESULTS: The number of methods in the Ligand Survey that failed to meet the goals for bias was 7 of 17 for thyroid-stimulating hormone and 11 of 13 for free thyroxine. The failure rates were 12 of 16 methods for thyroxine, 8 of 11 for triiodothyronine, and 9 of 11 for free triiodothyronine. The means of the analytic method for the proficiency testing material correlated significantly (P < .05) only with the fresh frozen serum means for thyroxine and thyroid-stimulating hormone in the Chemistry Survey and free triiodothyronine in the Ligand Survey. CONCLUSIONS: A majority of the methods used in thyroid function testing have biases that limit their clinical utility. Traditional proficiency testing materials do not adequately reflect these biases.

Calibration↗
PubMed2005

Total long-term within-laboratory precision of cortisol, ferritin, thyroxine, free thyroxine, and thyroid-stimulating hormone assays based on a College of American Pathologists fresh frozen serum study: do available methods meet medical needs for precision?

CONTEXT: It is important that the total long-term precision of laboratory methods meet the medical needs of the patients being served. OBJECTIVES: To determine the long-term within- and between-laboratory variation of cortisol, ferritin, thyroxine, free thyroxine, and thyroid-stimulating hormone measurements using commonly available methods and to determine if these variations are within accepted medical needs. DESIGN: Two vials of pooled frozen serum were mailed 6 months apart to laboratories participating in 2 separate College of American Pathologists surveys. The data from those laboratories that analyzed an analyte in both surveys were used to determine for each method the total variance and the within- and between-laboratory components. SETTING: The study included the A mailing of the 2003 College of American Pathologists Ligand Survey and the C mailing of the Chemistry Survey. MAIN OUTCOME MEASURES: For each analyte, total variance was partitioned into within- and between-laboratory components for each analytic method. The within-laboratory variations were then compared with imprecision criteria based on biological variation. PARTICIPANTS: The laboratories that reported results on the same analyte using the same method in both surveys. RESULTS: For each analyte, the median of the long-term within-laboratory variances of each peer group was 78% to 95% of its total-survey variance, and the median long-term within-laboratory coefficients of variation varied from 5.1% to 7.6%. The number of methods that met within-laboratory imprecision goals based on biological criteria were 5 of 5 for cortisol; 5 of 7 for ferritin; 0 of 7 for thyroxine and free thyroxine; and 8 of 8 for thyroid-stimulating hormone. CONCLUSIONS: For all analytes tested, the total within-laboratory component of variance was the major source of variability in this study. In addition, there are several methods, especially for thyroxine and free thyroxine, that may not meet analytic goals in terms of their imprecision.

Clinical Laboratory Techniques↗
PubMed2005

Comparison of fresh frozen serum to traditional proficiency testing material in a College of American Pathologists survey for ferritin, folate, and vitamin B12.

CONTEXT: Comparison of different analytical methods in proficiency surveys may be affected by the artificial nature of the survey material. OBJECTIVE: To compare intermethod differences in proficiency survey results between 2 types of survey material, conventional proficiency testing material (PTM) and fresh frozen human serum (FFS), for 3 markers of anemia: ferritin, folate, and vitamin B12. DESIGN: Data were gathered from a 2003 survey event in the College of American Pathologists Ligand ("K") Series, in which the specimens to be tested by each participating laboratory included 1 vial of FFS and 2 vials of PTM with different analyte concentrations. The more than 1600 laboratories subscribing to the survey were not advised as to the nature of the specimens. MAIN OUTCOME MEASURES: The bias of each method relative to the median of method means for each analyte and each type of survey material, and the interlaboratory coefficient of variation for each method. RESULTS: For each of the 3 analytes, moderate to large method biases were observed. For ferritin, method biases correlated strongly between comparable PTM and FFS specimens (Spearman r = 0.863, P < .001), whereas virtually no correlation was found for folate (r = -0.224, P = .48), and a marginally significant correlation existed for B12 (r = 0.55, P = .049). CONCLUSIONS: With ferritin, proficiency survey performance of PTM is similar to that of FFS, implying that method biases relate mainly to calibration. With folate and to a lesser extent with B12, PTM and FFS exhibit different method biases, implying that the biases reflect analyte heterogeneity and/or matrix effects.

Clinical Laboratory Techniques↗
PubMed2005

A comparison of human chorionic gonadotropin- related components in fresh frozen serum with the proficiency testing material used by the College of American Pathologists.

CONTEXT: As part of a College of American Pathologists (CAP) proficiency testing survey, a comparison is made between human chorionic gonadotropin (hCG) results from an actual patient pool and a similarly targeted artificial sample. The goal is to gain insight into the possible source(s) of bias attributable to the proficiency testing material (PTM) with a view toward creating more appropriate survey materials. OBJECTIVE: To compare hCG and related variants in a pool of fresh frozen sera (FFS) with that found in PTM. DESIGN: The 2003 CAP K/KN-A Survey included a FFS specimen along with admixtures of PTM. The FFS (K-02) and 1 PTM admixture (K-01) had similar mean hCG values. Five hCG-related analytes were measured on these 2 samples by a reference laboratory. PARTICIPANTS: Approximately 1800 clinical laboratories and diagnostic test kit manufacturers participated in the K/ KN-A Survey. MAIN OUTCOME MEASURES: Method imprecision (coefficient of variation) and method bias (relative difference between peer group mean and all-method median) were computed for the 2 samples. Differences were evaluated with respect to hCG-related analytes levels. RESULTS: All-method hCG results were 12.9 mIU/mL (12.9 IU/L) for the PTM material and 21.6 mIU/mL (21.6 IU/L) for the FFS material. Method biases for 14 manufacturers were greater for PTM than for FFS (-40% to +35% and -16% to +23%). Twelve of 14 methods had higher coefficients of variation on PTM. Total hCG and free beta hCG measurements by the reference laboratory were 14.1 mIU/ mL (14.1 IU/L) for the PTM material and 18.5 mIU/mL (18.5 U/L) for the FFS material (FFS), and 2.4 (PTM) and 0.7 (FFS) mIU/mL (2.4 and 0.7 IU/L), respectively. On a molar basis, free beta represented 17% and 4% of the total hCG, respectively. Levels of hyperglycosylated hCG, nicked hCG, and beta core fragment were not measurable in either sample. CONCLUSIONS: It is unlikely that the hCG added to the PTM is the source of the increased bias and variability. The main difference is a 3-fold increase in free beta found in the PTM, but methods previously found to strongly react with free beta were not systematically elevated. The biases between manufacturers found for the FFS specimen are likely attributable to calibration differences.

Chorionic Gonadotropin↗
PubMed2005

Comparison of fresh frozen serum to proficiency testing material in College of American Pathologists surveys: alpha-fetoprotein, carcinoembryonic antigen, human chorionic gonadotropin, and prostate-specific antigen.

CONTEXT: Most proficiency testing materials (PTM) contain an artificial matrix that may cause immunoassays to perform differently with this material than with clinical samples. We hypothesized that matrix effects would be reduced by using fresh frozen serum (FFS). OBJECTIVE: To compare the performance of an FFS pool to standard PTM for measurement of alpha-fetoprotein, carcinoembryonic antigen, human chorionic gonadotropin (hCG), and prostate-specific antigen (PSA). DESIGN: One FFS specimen and 4 different admixtures of PTM were distributed in the 2003 College of American Pathologists K/KN-A (for alpha-fetoprotein, carcinoembryonic antigen, hCG, and total and free PSA) and C-C (hCG only) Surveys. PARTICIPANTS: The number of laboratories that participated in the surveys varied from a low of 288 (free PSA, K/KN-A Survey) to a high of 2659 (hCG, C-C Survey). MAIN OUTCOME MEASURES: Method imprecision and method bias were compared between the FFS specimen and the standard PTM specimen with the closest value. Method imprecision was determined by calculating the coefficients of variation for each method and for all methods combined. Bias was defined as the proportional difference between peer-group mean and the median of all method means. RESULTS: The FFS specimen gave significantly higher imprecision than PTM for the analytes alpha-fetoprotein, carcinoembryonic antigen, total PSA, and free PSA. For hCG, no substantial imprecision differences were observed in both surveys. Bias was significantly greater for the alpha-fetoprotein, carcinoembryonic antigen, and total PSA assays and significantly lower for the hCG and free PSA assays when comparing the FFS with the PTM. CONCLUSIONS: Fresh frozen serum did not provide consistently lower imprecision or bias than standard PTM in a survey of commonly ordered tumor markers.

Carcinoembryonic Antigen↗
PubMed2004

Serum sex hormones and measures of benign prostatic hyperplasia.

BACKGROUND: Despite biologic plausibility, the associations between sex hormones and measures of benign prostatic hyperplasia (BPH) have not been consistently reported. METHODS: Subjects were randomly selected from the Olmsted County, MN population (n, 320; median age, 60.9 years) and followed biennially since 1990. In 2002, surrogate measures of BPH were assessed from an approximation of the American Urological Association Symptom Index (AUASI), Peak urinary flow rates (Q(max)), and a transrectal ultrasound assessment of prostate volume. Serum levels of prostate specific antigen (PSA), testosterone, bioavailable testosterone, and estradiol were also measured. RESULTS: Bioavailable testosterone levels declined with increasing cross-sectional age from 53.8, 50.2, to 41.2 ng/dl (P = 0.001) in men aged <60, 60-69, and >69 years, respectively, and the estradiol/bioavailable testosterone ratio increased from 0.042, 0.044, to 0.050 (P = 0.04). Among men with bioavailable testosterone above the median, estradiol levels had a dose response relationship with prostate size. Among men with bioavailable testosterone level </= the median, however, there was no association between estradiol level and prostate volume CONCLUSIONS: While cross-sectional, these findings suggest a more complex relationship between sex steroids and prostate volume in older men than simple independent effects.

Adult↗
PubMed2004

Sex-specific associations of lipoprotein(a) with presence and quantity of coronary artery calcification in an asymptomatic population.

BACKGROUND: Lipoprotein(a) (Lp(a)) is a potential risk factor for coronary artery disease (CAD). The relationship between serum Lp(a) and coronary artery calcification (CAC), a measure of subclinical coronary artery atherosclerosis, has not been extensively explored. MATERIAL/METHODS: Electron beam computed tomography was performed on 616 asymptomatic, white individuals (285 men) from a community-based study. Mean age was 57.2 years. Serum Lp(a) levels were measured by an immunoturbidimetric assay. Tobit regression was used to determine the sex-specific association of Lp(a) levels with presence and quantity of CAC. RESULTS: In women, Lp(a) was a significant predictor (P=0.0426) of presence and quantity of CAC after adjustment for age, hypertension status, waist circumference, presence of high low-density lipoprotein cholesterol (LDL-C), and history of smoking. In men, after adjusting for age, hypertension status, body mass index, presence of high LDL-C, and history of smoking, a positive interaction between Lp(a) and history of smoking (P=0.0387) was significantly associated with presence and quantity of CAC. CONCLUSIONS: Sex-specific relationships between Lp(a) and CAC provide evidence supporting sex-specific risk factor profiling for CAD. In women, Lp(a) alone may be an independent risk factor for coronary atherosclerosis, while in men, Lp(a) may confer higher risk conditional on the presence and level of other risk factors. The role of Lp(a) in the prediction and pathogenesis of subclinical coronary atherosclerosis needs to be further elucidated.

Adolescent↗
PubMed2004

Investigating the utility of serum cytokine measurements in a multi-institutional cancer anorexia/weight loss trial.

BACKGROUND: Interleukin-1 beta (IL-1beta), tumor necrosis factor alpha (TNFalpha), and interleukin-6 (IL-6) have been implicated in the cancer anorexia/weight loss syndrome. However, previous smaller studies have yielded conflicting results as to whether circulating, serum concentrations of these cytokines are in fact elevated. As the translational component of a large multi-institutional trial, this study assessed the clinical value of serum concentrations of these cytokines in patients with this syndrome. METHODS: Patients with incurable cancer with anorexia and/or weight loss were eligible. All underwent weekly weight measurements and appetite assessment for the first month and then monthly assessments thereafter. Serum was obtained at baseline and at 1 month, and all three cytokines were measured with the Immunolite assay. RESULTS: A total of 118 patients participated. At baseline, 99%, 54%, and 47% of patients' samples had undetectable IL-1beta, TNFalpha, and IL-6, respectively. Similar results were obtained at 1 month. No correlations were observed between serum cytokine concentrations and changes in weight or appetite. Baseline serum IL-6 predicted a diminished survival but only after adjustment for age and cancer site. CONCLUSION: Serum concentrations of IL-1beta, TNFalpha, and IL-6, as measured in this study, provide data of limited clinical value for patients with the cancer anorexia/weight loss syndrome.

Aged↗
PubMed2004

Interferences in hormone immunoassays.

Despite the numerous potential interferences that were discussed in this article, immunoassays, in general, are robust measurement systems. There is no practical way to identify specimens a priori that are likely to have immunoassay interference. Therefore, laboratories must rely on communication from clinicians to identify suspicious test values that may be caused by assay interference. After laboratories are alerted, multiple investigations can be undertaken. The common causes of immunoassay interferences (see Box I) are dependent on the analytic format. Competitive assays are most likely to have problems with cross-reactivity, whereas immunometric assays most often have problems with heterophile antibodies. The simple steps to test for dilutional linearity, spiked recovery, heterophile antibody blocking,and testing with alternate technology can help in the evaluations of cases that are suspected to have assay interference.

Hormones↗
PubMed2004

Clinical interpretation of reference intervals and reference limits. A plea for assay harmonization.

Reference intervals for healthy subjects and diseased populations are important benchmarks for the clinical interpretation of laboratory test values. It is important that the testing conditions used to collect the reference data be closely matched with the testing conditions used for patient data. Interlaboratory differences and intralaboratory changes, especially changes in analytic set-points, can markedly affect the clinical interpretation of tests. If laboratory testing methods could be harmonized, laboratories could potentially share reference data to make these data more reliable. This chapter illustrates the use of reference intervals for healthy subjects and reference data from diseased populations for medical decisions. One example illustrates the effects of age differences on test result interpretation. Other examples illustrate use of thyroid-stimulating hormone (TSH) and combinations of TSH with free thyroxine measurements for diagnosing thyroid diseases. Both univariate and multivariate reference intervals are discussed. Model systems for using disease prevalence and cost utility functions are provided to illustrate optimization of medical decisions.

Age Factors↗
PubMed2004

Lack of association between lipoprotein(a) and coronary artery calcification in the Genetic Epidemiology Network of Arteriopathy (GENOA) study.

OBJECTIVE: To investigate the relationship between lipoprotein(a) [Lp(a)] levels and the extent of coronary atherosclerosis in a cohort that consisted predominantly of hypertensive patients. PATIENTS AND METHODS: Patients were ascertained through sibships that contained at least 2 individuals with essential hypertension diagnosed before the age of 60 years. The 10-year coronary heart disease (CHD) risk was estimated on the basis of the Framingham risk equation. Serum Lp(a) was measured by an immunoturbidimetric assay. Coronary artery calcification (CAC) was measured noninvasively by electron beam computed tomography and CAC score calculated using the Agatston score. RESULTS: Patients included 765 non-Hispanic, white individuals (59% women) participating in the Genetic Epidemiology Network of Arteriopathy study. The mean +/- SD age of the patients was 62 +/- 8 years, and 77% had hypertension. The prevalence of detectable CAC was 87% in men and 60% in women. The CAC scores did not differ significantly across quintiles of Lp(a) levels in either men or women. In a multiple regression model that included conventional risk factors, Lp(a) levels were not related to CAC quantity in either sex. No significant interactions were noted between Lp(a) levels and the conventional risk factors in the prediction of CAC quantity. When stratified on the basis of the 10-year CHD risk, 26.5% of the patients were low risk (< 6%), 60.5% were intermediate risk (6%-20%), and 12.9% were high risk (> 20%). Lipoprotein(a) was not associated with CAC quantity within subgroups based on 10-year CHD risk. CONCLUSION: In this cohort enriched with hypertensive patients, the estimated 10-year CHD risk did not appear to modify the lack of an association between Lp(a) levels and CAC.

Aged↗
PubMed2004

MUC1 gene-derived glycoprotein assays for monitoring breast cancer (CA 15-3, CA 27.29, BR): are they measuring the same antigen?

CONTEXT: There are 2 general types of assays measuring MUC1 gene-derived glycoprotein: assays for cancer antigen (CA) 15-3, which are sandwich assays, and assays for CA 27.29, which are competitive assays. These 2 types of assays measure slightly different parts of this tandem-repeat molecule. Across-method assay differences hinder the exchange of patient test values among integrated health care networks and among countries. OBJECTIVE: This report evaluates the method differences among these assays to determine if the differences between these assays are mainly related to variations in calibration or differences in analyte specificity. DESIGN: Data from 22 College of American Pathologists survey challenges were analyzed to compare 10 commercial assay methods for these 2 related analytes. In addition, data from 58 patient samples were analyzed to compare 3 of these assays. RESULTS: The linear correlation coefficients comparing the within-method medians of these proficiency test distributions were very high (>0.99) for all of the methods; however, the regression slopes varied from 0.836 to 1.095. The regression slopes for the patient specimens varied similarly, but the correlation coefficients were lower. CONCLUSIONS: This study indicates that many of the test value differences for these measurements are due to differences in assay calibration rather than differences in the specificity of the assay measurement systems. Survey test data potentially could be used to help harmonize these assay differences.

Antibody Specificity↗
PubMed2004

How sensitive is a prostate-specific antigen measurement? How sensitive does it need to be?

Assays are now available that can measure very low concentrations of prostate-specific antigen (PSA), but their analytic performance and clinical utility are not well defined. This brief article highlights some of the clinical issues related to the limited prognostic significance of small changes in PSA concentrations in men with prostate cancer who have been treated with prostate ablation therapy. College of American Pathologists proficiency survey data are presented, illustrating the performance of commercial PSA assays with low PSA concentration survey samples tested between 1998 and 2002. The performance of the assays appears to be improving, but many of the currently used assays have intralaboratory coefficients of variation greater than 20% for PSA concentrations less than 0.4 ng/mL. Also, there are major differences in the level of PSA reported by various assays in these low concentration samples. These level differences (if they are also seen in clinical samples) may cause clinical problems when fixed serum PSA thresholds (eg, 0.2 ng/mL) are used to make clinical decisions related to prostate tumor recurrence.

Humans↗