What we still do not know about adrenal vein sampling for primary aldosteronism.

During the last two decades, primary aldosteronism has emerged as the most common cause of secondary hypertension, and advances in the diagnosis and treatment of this condition have improved patient care substantially. A major stumbling block in the evaluation and management of these patients, which ultimately guides treatment and prognosis, is answering the question, "Which adrenal gland(s) produce aldosterone?" Adrenal vein sampling has emerged as the only reliable method to determine the answer to this question; however, the methodology and criteria for lateralization have been determined empirically with little prospective data. The major remaining controversies surrounding adrenal vein sampling include: who should perform and who should undergo the procedure; what criteria should be used to define a successful study and lateralization of aldosterone production; whether cosyntropin should be infused during the procedure and how; and what to do when results are ambiguous? This article reviews some of the advances in the execution of this procedure, the variations in procedure, the data that fuel the controversies, and the issues that need to be resolved in the future.

Assessment of HER-2/neu status in breast cancer. Automated Cellular Imaging System (ACIS)-assisted quantitation of immunohistochemical assay achieves high accuracy in comparison with fluorescence in situ hybridization assay as the standard.

This retrospective study of formalin-fixed infiltrating breast cancer specimens compared manual immunohistochemical assay with a new image analyzer-assisted immunohistochemical quantitation method, using fluorescence in situ hybridization assay (FISH) as the standard. Following the manual immunohistochemical assay, 189 cases, including most manual immunohistochemically positive and some random negative cases, were analyzed by FISH assay for Her-2/neu gene amplification and by the Automated Cellular Imaging System (ACIS) for immunohistochemical staining. Using the FISH standard, the ACIS immunohistochemical assay attained a higher concordance rate and sensitivity than the manual immunohistochemical assay (91.0% and 88% vs 85.7% and 71%, respectively), with only a slight decrease in specificity (93% vs 96%, respectively). In particular, the ACIS immunohistochemical assay resulted in a higher correlation with the FISH assay in the manual immunohistochemical assay 2+ cases. The ACIS immunohistochemical assay achieved higher accuracy than the manual method according to receiver operating characteristic curve analysis. The ACIS method represents a substantial improvement over the manual method for objective evaluation of the HER-2/neu status.

Gene therapy to prevent organophosphate intoxication.

The specific hydrolytic activity of PON1 paraoxonase/arylesterase enzymes in liver and blood provides a natural barrier against the entry of organophosphate toxins into the central and peripheral nervous systems. Inherited differences in PON1 enzyme concentrations may determine levels of susceptibility to organophosphate injury in humans. To test whether boosting serum levels of PON1 enzymes by gene therapy might provide increased protection, we compared the degree of inactivation of whole brain acetylcholinesterase of mice exposed to chlorpyrifos 4 days after intravenous injection of recombinant adenoviruses containing PON1-LQ or PON1-LR genes or no PON1 gene. Both recombinant viruses containing PON1 genes boosted serum arylesterase concentrations by approximately 60% and significantly prevented the inactivation of brain acetylcholinesterase. Some mice were completely protected. These findings indicate that boosting serum levels of PON1 enzymes by a gene delivery vector raises the threshold for organophosphate toxicity by hydrolytic destruction before the chemical can enter the brain.

Discriminating between iron deficiency anemia and anemia of chronic disease using traditional indices of iron status vs transferrin receptor concentration.

We compared the ability of soluble serum transferrin receptor (TfR) concentration, quantified using the R&D Systems (Minneapolis, MN) enzyme-linked immunosorbent TfR assay, with other, more traditional indicators of iron status (total iron binding capacity [TIBC], mean corpuscular volume [MCV], percent transferrin saturation [%TS], RBC distribution width [RDW], and serum iron concentration [SIC]) for discriminating between patients with iron deficiency anemia (IDA) or anemia of chronic disease (ACD). The TfR concentration was determined in 72 serum samples selected from men and nonpregnant women classified biochemically on the basis of ferritin concentration as having IDA (n = 41) or ACD (n = 31). By using receiver operating characteristic curve analysis, the diagnostic accuracy of the various indicators of iron status that we evaluated for discriminating between IDA and ACD decreased in the following order: TIBC > TfR > MCV > (%TS = RDW) > SIC. There was no significant difference between the diagnostic accuracy of TIBC and TfR. Thus, the routine measurement of TfR offers no advantage over TIBC for discriminating between people with biochemically defined IDA or ACD.

Soluble transferrin receptor (sTfR) concentration quantified using two sTfR kits: analytical and clinical performance characteristics.

We compared the analytical and clinical performance characteristics of the Ramco and R&D Systems enzyme-linked immunosorbent assays (ELISAs) for quantifying serum levels of soluble transferrin receptor (sTfR). In addition, we determined both the number of samples required to determine the true individual mean sTfR concentration for a single individual and the critical difference (CD) between serial measurements that indicates a statistically significant change in sTfR concentration. sTfR concentration was determined in 127 serum samples selected retrospectively from males (n=32) and non-pregnant (n=40) and pregnant women (n=55). Intra- and inter-assay precision for both methods was good (CV values 5--10%) to excellent (CV values <5%) over a wide range of sTfR concentrations. Correlation between these methods was good (r=0.93); however, sTfR values by the R&D kit were approximately 2.9 times higher than values obtained using the Ramco kit on the same serum samples. Nevertheless, receiver-operator characteristic (ROC) curve analysis demonstrated that the diagnostic accuracy of both assays in discriminating between patients with iron-deficiency anemia (IDA) or anemia of chronic disease (ACD) was high (area-under-the-curve (AUC) values >0.95) and not significantly different (P=0.480). We determined that a minimum of 8 samples are required to determine an individual's true sTfR concentration, while a >40% difference between serial sTfR measurements would be required to indicate a statistically significant change in sTfR concentration. We concluded that both the Ramco and R&D Systems sTfR methods have similar analytical and clinical performance characteristics and were likely to be equally useful in discriminating between patients with biochemically defined IDA or ACD.

The validity of quick intraoperative parathyroid hormone assay: an evaluation in seventy-two patients based on gross morphologic criteria.

BACKGROUND: Parathyroidectomy for primary hyperparathyroidism has conventionally required identification of all parathyroid glands with excision of grossly abnormal glands. Using this approach, cure rates exceed 95%. Directed cervical exploration has been advocated using quick intraoperative parathyroid hormone (QPTH) assay with preoperative localization. Adoption of this approach requires validation of the accuracy of QPTH assay. METHODS: Patients with primary hyperparathyroidism undergoing bilateral neck exploration during a 31-month period were reviewed. Uniglandular (UGD) or multiglandular (MGD) disease was determined by gross morphologic criteria. QPTH assays were performed before skin incision and at 5, 10, and 20 minutes after excision of each abnormal gland. A 10-minute QPTH decrease of 50% from baseline levels indicated curative excision. These data were not used to guide extent of exploration or tissue resection. RESULTS: Of 72 patients, 55 (76%) had UGD and 17 (24%) had MGD. QPTH assay accurately predicted the disease state in 89%. Four (7%) UGD patients did not have an appropriate QPTH decline at 10 minutes. Four (24%) MGD patients had an inappropriate QPTH decline at 10 minutes. CONCLUSIONS: Using QPTH guided exploration, 6% (4 of 72) of patients would undergo unnecessary extended exploration and 6% (4 of 72) (95% CI, 1% to 13%) may require reoperation for unidentified MGD. These results validate the accuracy of QPTH assay.

Bisalbuminuria in an adult with bisalbuminemia and nephrotic syndrome.

Bisalbuminemia (or alloalbuminemia) is a relatively rare hereditary or acquired condition characterized by the presence of two distinct albumin bands, or, less commonly, a single widened albumin band, after agarose gel electrophoresis of serum. Bisalbumins are caused by point- or chain-mutations that occur with a population frequency of 1:10,000 to 1:1000. Although no adverse clinical effects have been attributed to bisalbumins, some albumin variants have altered affinity for steroid hormones, thyroxine, or drugs. We report a case of bisalbuminuria in a 25-year-old man with bisalbuminemia and nephrotic syndrome.

Transient adhesion of platelets in pump-oxygenator systems: influence of SMA and nitric oxide treatments.

We employed gamma scintigraphy to quantify the transient accumulations of platelets in pump-oxygenator systems employed in cardiopulmonary bypass (CPB). A flat sheet microporous polypropylene membrane oxygenator (Cobe Duo) was employed, with and without siloxane/caprolactone oligomer coating (SMA) (n = 8 each). The effect of nitric oxide gas infusion on platelet deposition was also evaluated for the uncoated Cobe Duo system (n = 10 each). Scintigraphic images of radiolabelled cells were obtained and converted to numbers of all platelets, labeled and unlabeled, adhering to the pump and oxygenator surfaces. These numbers were compared, by study group, for a 90-min period of normothermic CPB in the adult pig, employing standard prime and anticoagulation regimens. Platelets adhered in large numbers to control oxygenators, reaching maxima (> 20% of the circulating platelet mass) 30 min following institution of CPB, and decreasing for the duration of CPB. SMA treatment significantly decreased platelet adhesion following a 5-10-min transient accumulation period. Nitric oxide infusion significantly reduced platelet adhesion throughout the CPB period. Platelet accumulations on the high fluid shear centrifugal pump surfaces increased monotonically to maxima at about the same time as for the oxygenators, but did not decrease thereafter. Higher platelet surface densities were observed on the centrifugal pump surfaces than on the oxygenator surfaces. CPB with the untreated circuit tended to reduce circulating platelet counts vs theoretical values based on hemodilution alone. In contrast, SMA significantly increased the circulating platelet count versus the untreated control group. These results indicate that platelet adherence to the foreign surfaces of CPB equipment are influenced in characteristic ways by time and fluid shear. SMA treatment and nitric oxide infusion both reduce platelet adhesion to oxygenator surfaces. SMA treatment spares these cells for the circulation.

Maternal cardiac troponin I levels during normal labor and delivery.

OBJECTIVE: Diagnosis of myocardial infarction in pregnant women on the basis of changes in biochemical markers is complicated by the release of some of these markers from noncardiac tissue sources. We compared troponin I levels with those of other markers in normal pregnant women. STUDY DESIGN: In 51 healthy women at term in labor, cardiac troponin I, myoglobin, creatine kinase, and creatine kinase MB levels were determined at admission, during the second stage of labor, and within 30 minutes, 12 hours, and 24 hours after delivery. RESULTS: Mean admission levels for all markers were below the upper limit of normal. Mean concentrations of myoglobin, creatine kinase, and creatine kinase MB mass were increased nearly twofold within 30 minutes after delivery. The highest level of troponin I (0.134 ng/mL) at all time points was below the cutoff value (0.15 ng/mL) for discriminating myocardial infarction. CONCLUSIONS: Because only troponin I levels remained undetectable during and after delivery, it is potentially the most useful biochemical marker for monitoring pregnant women for myocardial injury.

Comparison of instrument-read dipsticks for albumin and creatinine in urine with visual results and quantitative methods.

Three hospital sites evaluated the Bayer two-pad urine dipstick as a screening test for microalbuminuria. One pad estimates albumin concentrations between 10 and 150 mg/L, and the second estimates creatinine values between 300 and 3,000 mg/L. The Boehringer Mannheim (BMD) Micral dipstick was also compared and evaluated. The accuracy of the dipsticks was judged by comparison with cuvet-based immunonephelometry for albumin and to standard rate-Jaffe methods for creatinine; these assays were well standardized and controlled and were assumed to give accurate values. Precision of these methods and that of the dipsticks was determined by multiple assays of control materials. Visual or instrument (Clinitek 50 or 100) evaluation of the Bayer or visual checks of the BMD albumin dipstick pad with patients' urines gave clinically acceptable accuracy. The albumin/creatinine ratio from the Bayer dipsticks gave better accuracy for albumin excretion than the albumin pads alone from either manufacturer. This ratio should permit making a good estimate of the 24-hr albumin excretion in a randomly collected urine.

Regulation of biologically active dimeric inhibin A and B from infancy to adulthood in the male.

Inhibins are glycoprotein members of the transforming growth factor-beta family that have been implicated in the control of spermatogenesis by exerting a negative feedback on FSH secretion. In addition, locally produced inhibins may play a role in paracrine regulation of testicular function. Immunoassays were used to measure the two biologically active dimeric forms of inhibin (inhibin A and B) in serum, seminal plasma, and urine. To better define their actions, inhibins were measured in the male during infancy, sexual maturation, and senescence. Inhibin B but not A was measurable in the serum of male newborns, infants, children, and adults. In adult males, measurable levels of inhibin B were detected in the seminal plasma but not the urine. The circulating levels of inhibin B increased shortly after birth and peaked at 4-12 months of age (210 +/- 31 pg/mL). The concentration measured in the serum then decreased to a low of 81 +/- 12 pg/mL of inhibin B from 3-9 yr of age followed by a gradual increase beginning with the onset of puberty and reaching another peak of 167 +/- 20 pg/mL in males who were 20-30 yr of age. Inhibin B levels then gradually declined with increasing age up through 90 yr of age. Serum levels of gonadotropins and total testosterone production were also measured in these same males. There was a brief increase in the gonadotropins (FSH and LH) during the few months of postnatal development, followed by a decrease to basal levels until the onset of puberty at 10-14 yr of age. Testosterone was also increased in the serum of infants from day 1 through 12 months of age, which decreased in young children but increased again following the elevation of gonadotropins during puberty. In adults aged 20-90 yr, serum levels of inhibin B were inversely proportional to levels of FSH but not LH or testosterone. In males in which a semen analysis was performed, those males with normal semen analysis had a significantly higher inhibin B levels, sperm production, and lower FSH levels than males with either oligospermia or nonobstructive azoospermia. The levels of Inhibin B found in circulation were a good marker for testicular function and could be useful in the diagnosis of patients with semen abnormalities or a complete absence of spermatogenesis. Because this glycoprotein is secreted in high amounts in the prepubertal testis up to 3 yr of age, inhibin B could potentially be used as a marker in the diagnosis of cryptorchidism and precocious puberty.

Cardiac troponin I measurement with the ACCESS immunoassay system: analytical and clinical performance characteristics.

We evaluated the ACCESS cardiac troponin I (cTnI) immunoassay as a marker for myocardial infarction (MI). Total imprecision was 6.0% to 13.5%, the minimum detectable concentration was 0.007 microg/L, and the limit of quantitation was 0.046 microg/L. Comparison of cTnI measurement between the ACCESS and Stratus systems (n = 114) showed a proportional difference: ACCESS cTnI = 0.0996 Stratus cTnI + 0.049 microg/L (r = 0.811). Fifty-nine of 61 ambulatory patients without cardiac symptoms had no detectable cTnI (95% range, 0.00 to 0.025 microg/L). The optimum cutoff for discriminating MI (n = 289, 45 with MI) was 0.15 microg/L by receiver operator characteristic curve analysis; at this cutoff, the ACCESS cTnI assay showed a sensitivity of 88.9% (95% CI, 79.7-98.1%) and specificity of 91.8% (95% CI, 88.4-95.2%). The ACCESS cTnI assay results showed 89.4% and 93.0% concordance with the MB isoenzyme of creatine kinase (CK-MB) mass and Stratus cTnI results, respectively, for classification of patients with suspected MI. The ACCESS cTnI assay appears to show sensitivity and specificity comparable with those of both CK-MB mass and Stratus cTnI assays for the diagnosis of MI in patients presenting within 12 h of onset of symptoms.

Influence of cardiopulmonary bypass on platelet and neutrophil accumulations in internal organs.

The authors employed gamma scintigraphy to quantify the post bypass accumulations of platelets and neutrophils in the lung, liver, and heart of adult pigs subjected to a standard 90 min regimen of normothermic cardiopulmonary bypass (CPB). Coated and uncoated microporous polypropylene oxygenator circuits were studied for Cobe Duo (Arvada, CO) oxygenators (amphophilic silicone-caprolactone oligomer [SMA] coating, n = 8 each) and Medtronic Maxima (Irvine, CA) oxygenators (Carmeda heparin coating, n = 5 each). Images of cells in the organs (deposited + blood pool) were corrected for tissue absorption and other factors and compared for a 2 hr period post CPB, using repeat measures ANOVA and rank tests. Platelet accumulations in internal organs correlated positively with whole blood platelet counts and negatively with platelet deposits in oxygenators during CPB. In general, uncoated CPB circuits significantly reduced platelet and neutrophil accumulations in lung, liver, and heart versus preCPB controls for the post CPB interval, for both systems. The SMA treatment significantly increased platelet accumulations versus uncoated controls in lung, liver, and heart for the 2 hr period, including the majority of the post CPB sampling intervals; platelet densities did not reach preCPB levels. Neutrophil accumulations were unaffected by the SMA coating. Carmeda heparin treatment significantly increased platelet accumulations in the liver, but not lung or heart. Despite preservation of circulating neutrophils observed with the Carmeda heparin treatment, neutrophil accumulations in internal organs were not elevated post CPB.

Antibody panels in idiopathic polyneuropathy and motor neuron disease.

We prospectively evaluated patients with idiopathic polyneuropathy (PN) and motor neuron disease (MND) with commercial antibody (Ab) panels. Patients with sensorimotor PN received a "sensorimotor neuropathy profile" [3-sulfated glucuronyl paragloboside (SGPG)/myelin-associated glycoprotein (MAG), GM1, asialo-GM1, GD1b, Hu, sulfatide]. Motor neuropathy or MND patients underwent a "motor neuropathy profile" (SGPG/MAG, GM1, asialo-GM1). Seven of 78 patients (9.0%) with sensorimotor PN and 3 of 44 patients (6.8%) with MND had abnormal panels. None of 60 patients with axonal sensory or sensorimotor PN had antisulfatide Ab. Seven of 13 patients (54%) with multifocal motor neuropathy had abnormal panels, with 6 seropositive to GM1. We found abnormal Ab panels in fewer than 10% of patients with idiopathic sensorimotor PN and MND. Moreover, abnormal Ab tests often did not relate to the clinical context. Our data do not support the use of commercial Ab panels in the evaluation of patients with idiopathic PN or MND.

Evaluation of neurologic function in Gulf War veterans. A blinded case-control study.

OBJECTIVE: To determine whether Gulf War-related illnesses are associated with central or peripheral nervous system dysfunction. DESIGN: Nested case-control study. PARTICIPANTS: Twenty-three veterans with factor analysis-derived syndromes (the cases), 10 well veterans deployed to the Gulf War (the deployed controls), and 10 well veterans not deployed to the Gulf War (the nondeployed controls). METHOD: With investigators blinded to group identities, participants underwent objective neurophysiological, audiovestibular, neuroradiological, neuropsychological, and blood tests. MAIN OUTCOME MEASURES: Evidence of neurologic dysfunction. RESULTS: Compared with the 20 controls, the 23 cases had significantly more neuropsychological evidence of brain dysfunction on the Halstead Impairment Index (P=.01), greater interside asymmetry of the wave I to wave III interpeak latency of brain stem auditory evoked potentials (P=.02), greater interocular asymmetry of nystagmic velocity on rotational testing, increased asymmetry of saccadic velocity (P=.04), more prolonged interpeak latency of the lumbar-to-cerebral peaks on posterior tibial somatosensory evoked potentials (on right side, P=.03, and on the left side, P=.005), and diminished nystagmic velocity after caloric stimulation bilaterally (P values range from .02 to .04). Cases (n=5) with syndrome 1 ("impaired cognition") were the most impaired on brain stem auditory evoked potentials (P=.005); those (n=13) with syndrome 2 ("confusion-ataxia") were the most impaired on the Halstead Impairment Index (P=.006), rotational testing (P=.01), asymmetry of saccadic velocity (P=.03), and somatosensory evoked potentials (P< or =.01); and those (n=5) with syndrome 3 ("arthro-myo-neuropathy") were the most impaired on caloric stimulation (P< or =.01). CONCLUSIONS: The 3 factor-derived syndromes identified among Gulf War veterans appear to represent variants of a generalized injury to the nervous system.

Immunonephelometric quantification of group-specific component protein in patients with acute liver failure.

Serum levels of group-specific component (Gc) protein are useful in evaluating the likelihood of survival in patients with acute liver failure (ALF) who may be candidates for liver transplant surgery. Most methods for quantifying Gc protein concentration are either isotopic, manual, technically demanding, and/or time consuming to perform, and thus are not well suited for routine clinical use in a hospital setting. We modified and evaluated a recently described nonisotopic, fully automated, immunonephelometric method for quantifying serum Gc protein concentration and compared it to our previous immunoblotting method. In addition, we evaluated the effect of G-actin on the immunonephelometric measurement of Gc protein. Serum samples from 20 patients with ALF and from 20 age- and sex-matched clinic patients without liver disease were quantified by both immunoblotting and immunonephelometry. We assessed the intra-assay precision, correlation, and diagnostic accuracy of these methods in discriminating between individuals with no preexisting liver disease and those with ALF. Actin in 1.3- to 4-fold excess of Gc protein levels demonstrated minimal to no interference in the quantification of Gc protein by immunonephelometry. Immunonephelometry was more precise than immunoblotting. Gc protein values by immunonephelometry were similar to those obtained by immunoblotting, and the diagnostic accuracy of Gc protein concentration by immunonephelometry was similar to that observed by immunoblotting. Immunonephelometry provides a nonisotopic, fully automated, rapid, precise, accurate, and cost-effective method for quantifying serum levels of total Gc protein that is well suited for routine use in a hospital-based clinical laboratory.

Comparison of three assays for total serum prostate-specific antigen and percentage of free prostate-specific antigen in predicting prostate histology.

OBJECTIVES: To determine the statistical performance of three different assays for prostate specific antigen (PSA) and the percentage of free PSA with respect to the differentiation of histologic benign prostatic hyperplasia (BPH) and prostate cancer in men who underwent surgical removal of prostate tissue. METHODS: Serum of 86 men scheduled for prostate surgery (transurethral resection of the prostate [TURP], simple open prostatectomy, radical prostatectomy, cystoprostatectomy) was frozen and subjected to measurement in batches using three different assays for total PSA (Hybritech Tandem-E, Abbott IMx, Tosoh AIA-600) and free PSA by the Hybritech method after a single freeze-thaw cycle. The histologic diagnosis of the removed tissue (35 BPH and 51 cancer) was used as a "gold standard" for classification of disease status. Sensitivity, specificity, positive and negative predictive values, and diagnostic efficiency were calculated for the three total PSA assays and the free/total PSA ratios for the entire cohort and subsets. Receiver-operating characteristic (ROC) curve analysis was used to compare the performance of the assays and ratios. RESULTS: Mean and median total PSA values differed slightly between the three assays for all patients, and for those with BPH and cancer, but this difference was not significant. Because of a considerable overlap, the differences between the mean PSA values for men with BPH and prostate cancer were not significant. At a cutpoint of 4.0 ng/mL, sensitivity with respect to the differentiation between BPH and prostate cancer was 68.6% for all three total PSA assays; the respective AUCs (0.613-0.625) were not significantly different. While the performance of the free/total PSA ratios was superior, the differences were only significant when subsets of patients were considered with a total PSA between 4 and 10 ng/mL or 4 and 15 ng/mL (AUCs 0.789-0.816). Likewise, sensitivity, specificity, and diagnostic efficiency was better in these subsets of patients. CONCLUSIONS: In this study in which a "gold standard" based on histologic analysis of the entire (or large part of) the prostate gland was used to classify disease status, the three assays for total serum PSA (Hybritech Tandem-E, Abbott IMx, and Tosoh AIA-600) performed very similarly with identical sensitivities (at a cutpoint of 4.0 ng/mL) and comparable AUCs with respect to the differentiation of men with histologic BPH and prostate cancer. The ratios of free/total PSA calculated as free PSA by the Hybritech manual immunoradiometric assay (IRMA) method over all three total PSA assays, performed marginally better in the entire patient population. However, in the subsets of patients with a PSA of 4-10 ng/mL and 4-15 ng/mL, all three ratios performed significantly better than the three total PSA assays. The proper choice of a cutpoint for the ratio (15%, 17%, 19%, or 21%) depends on the desirability of maximizing either sensitivity or specificity while optimizing diagnostic efficiency.

Analytical performance characteristics of the T4 method in the Abbott AxSYM immunoassay analyzer.

OBJECTIVE: To evaluate the tetraiodothyronine (T4) method in the Abbott AxSYM immunoassay analyzer. DESIGN: The single-value criteria proposed by Westgard et al. were employed. Assays of control materials established random error (RE) analytical sensitivity, and linearity. Constant error (CE) was established by studying the effects of interferents on T4 quantification. The AxSYM random access immunoassay analyzer was compared with TDx batch analyzer to determine systematic error (SE). Critical concentrations of T4 are 3.0 micrograms/dL and 13.0 micrograms/dL, as these concentrations represent medical decision points. Allowable error at these critical concentrations are 1.0 and 2.6, respectively. SETTING: Peninsula Regional Medical Center Clinical Laboratories. RESULTS: Based on Health Care Financing Administration [HCFA] allowable error goals, RE, SE, and CE were acceptable for concentrations of T4 ranging from 3.0 micrograms/dL to 13 micrograms/dL. PE was virtually absent. Total error (TE) = RE + SE was acceptable at 13 micrograms/dL but exceeded allowable error at the lower critical value of 3.0 micrograms/dL. Abbott AxSYM was sensitive to T4 at a concentration of 0.34 microgram/dL. Linearity was excellent and consistent with the manufacturer's claim over a range 1.0 microgram/dL to 24 micrograms/dL. Of the interferents studied only hemoglobin caused a > 15% change in the measurement of T4. CONCLUSION: The AxSYM immunoasssay analyzer performed to manufacturer's specifications and met HCFA allowable error limits for quantifying T4.