Clinical Impact of New Reference Intervals for the Roche Prolactin II Immunoassay.

Context: The Roche prolactin immunoassay is used throughout the world. It reports higher values than the Siemens immunoassay but the manufacturer-defined reference intervals are similar. Patient results are often above the Roche upper limit but within the Siemens interval, causing diagnostic confusion. Objective: Establish new reference intervals for the Roche and Siemens prolactin immunoassays. Methods: We established new reference intervals for the Roche and Siemens immunoassays using 374 specimens from healthy outpatients. We performed chart review for unnecessary testing and treatment for 298 patients in a 6-month period with at least 1 Roche prolactin value above the manufacturer-defined upper limit and below our new upper limit. Results: The new upper limit for the Roche assay was 37.8 ng/mL (females) and 22.8 ng/mL (males). The manufacturer-defined limits were 23.3 ng/mL and 15.2 ng/mL, respectively. New intervals for the Siemens assay matched the manufacturer. No cases of clinically significant pathophysiologic prolactin excess were identified in patients with values between the manufacturer-defined upper reference limit and our new Roche upper limit. Unnecessary further evaluation in these patients included 459 repeat prolactin measurements, 57 macroprolactin measurements, 39 magnetic resonance imaging studies, and 28 endocrine referrals. Eleven patients received dopamine agonists. The minimum cost of excess care using Medicare reimbursement rates was $34 134, with substantially higher amounts billed to patients and their insurance providers. Conclusion: Adoption of new upper reference limits for the Roche prolactin assay of 37.8 ng/mL (females) and 22.8 ng/mL (males) would not delay diagnosis or necessary intervention in patients with clinically significant pituitary tumors but would reduce unnecessary evaluation in patients without pathophysiologic prolactin excess.

Mistaken Identity: The Role of Autoantibodies in Endocrine Disease.

BACKGROUND: Autoimmune endocrine diseases can be thought of as a case of mistaken identity. The immune system mistakenly attacks one's own cells, as if they were foreign, which typically results in endocrine gland hypofunction and inadequate hormone production. Type 1 diabetes mellitus and autoimmune thyroid disorders (Hashimoto and Graves diseases) are the most common autoimmune endocrine disorders, while conditions such as Addison disease are encountered less frequently. Autoantibody production can precede clinical presentation, and their measurement may aid verification of an autoimmune process and guide appropriate treatment modalities. CONTENT: In this review, we discuss type 1 diabetes mellitus, autoimmune thyroid disorders, and Addison disease, emphasizing their associated autoantibodies and methods for clinical detection. We will also discuss efforts to standardize measurement of autoantibodies. CONCLUSIONS: Autoimmune endocrine disease progression may take months to years and detection of associated autoantibodies may precede clinical onset of disease. Although detection of autoantibodies is not necessary for diagnosis, they may be useful to verify an autoimmune process.

National Kidney Foundation Laboratory Engagement Working Group Recommendations for Implementing the CKD-EPI 2021 Race-Free Equations for Estimated Glomerular Filtration Rate: Practical Guidance for Clinical Laboratories.

Recognizing that race is a social and not a biological construct, healthcare professionals and the public have called for removal of race in clinical algorithms. In response, the National Kidney Foundation and the American Society of Nephrology created the Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases to examine the issue and provide recommendations. The final report from the Task Force recommends calculating estimated glomerular filtration rate (eGFR) without a race coefficient using the recently published CKD-EPI 2021 creatinine (cr) and creatinine-cystatin C (cr-cys) equations. The Task Force recommends immediately replacing older eGFRcr equations (MDRD Study and CKD-EPI 2009) with the new CKD-EPI 2021 equation. In a 2019 survey by the College of American Pathologists, 23% of 6200 laboratories reporting eGFRcr used an incorrect equation that is not suitable for use with standardized creatinine measurements, 34% used the CKD-EPI 2009 equation and 43% used the MDRD Study 2006 equation re-expressed for standardized creatinine measurement. Rapid transition to using the CKD-EPI 2021 equation is an opportunity for laboratories to standardize to a single equation to eliminate differences in eGFRcr due to different equations used by different laboratories, and to report eGFR without use of race. We provide guidance to laboratories for implementing the CKD-EPI 2021 equations for both eGFRcr and eGFRcr-cys.

Validation study of the Access antimüllerian hormone assay for the prediction of poor ovarian response to controlled ovarian stimulation.

OBJECTIVE: To evaluate the diagnostic performance of the antimüllerian hormone (AMH) level determined using the Access AMH assay for predicting poor ovarian response (POR) defined as ≤4 oocytes retrieved, including the validation of the predefined AMH cutoff of 0.93 ng/mL in both serum and plasma. DESIGN: Prospective cohort study. SETTING: Fifteen private and academic fertility centers (14 in the United States and 1 in Canada). PATIENT(S): Women aged 21-45 years planning controlled ovarian stimulation for in vitro fertilization. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Number of oocytes retrieved, categorized as POR and normal-to-high ovarian response (non-POR). The correlation of AMH level and antral follicle count. RESULT(S): Data were available for 472 participants who completed the study (74 with POR and 398 non-POR). The mean AMH serum level among those with POR was 0.99 ng/mL (median 0.76 ng/mL) compared with 2.83 ng/mL (median 2.36 ng/mL) among the normal-to-high responders. For confirmation of the 0.93 ng/mL AMH level cutoff as a predictor of POR, a receiver operating characteristic analysis gave an area under the curve of 0.852, with corresponding sensitivity and specificity of 63.5% and 89.2%, respectively. The associated positive predictive value was 52.2% and the negative predictive value was 92.9%. The AMH plasma values demonstrated a strong correlation with AMH serum values with an r value = 0.9980. The previously established AMH cutoff of 1.77 ng/mL for antral follicle count >15 resulted in a sensitivity of 83.8% (95% confidence interval [CI] 77.7-88.5) and a specificity of 59.9% (95% CI 54.2-65.4). CONCLUSION(S): This study validated the previously established AMH cut-point for the prediction of POR. Because this cut-point may vary depending on the assay used, the specific AMH assay should be reported in the literature whenever possible.

Evaluation of 3 SARS-CoV-2 IgG Antibody Assays and Correlation with Neutralizing Antibodies.

BACKGROUND: As serologic assays for SARS-CoV-2 become more widely utilized, it is important to understand their performance characteristics and correlation with neutralizing antibodies. We evaluated 3 commonly used SARS-CoV-2 IgG assays (Abbott, DiaSorin, and EUROIMMUN) for clinical sensitivity, specificity, and correlation with neutralizing antibodies, and then compared antibody kinetics during the acute phase of infection. METHODS: Three panels of samples were tested on every assay. Sensitivity was assessed using a panel of 35 specimens serially collected from 7 patients with RT-PCR-confirmed COVID-19. Specificity was determined using 100 sera samples collected in 2018 from healthy individuals prior to the outbreak. Analytical specificity was determined using a panel of 37 samples from individuals with respiratory illnesses other than COVID-19. RESULTS: Clinical sensitivity was 91.43% (95% CI 76.94-98.20%) for Abbott, and 88.57% (95% CI 73.26-96.80%) for both DiaSorin and EUROIMMUN. Clinical specificity was 99.00% (95% CI 94.55-99.97%) for Abbott and DiaSorin and 94.00% (95% CI 87.40-97.77%) for EUROIMMUN. The IgG assays demonstrated good qualitative agreement (minimum of 94%) and good correlation between the quantitative result for each combination of assays (r2 ≥ 0.90). The neutralizing antibody response did not necessarily follow the same temporal kinetics as the IgG response and did not necessarily correlate with IgG values. CONCLUSION: The 3 IgG antibody assays demonstrated comparable performance characteristics. Importantly, a qualitative positive IgG result obtained with any of the assays was associated with the presence of neutralizing antibodies; however, neutralizing antibody concentrations did not correlate well with signal to cutoff ratios.

An Intact ACTH LC-MS/MS Assay as an Arbiter of Clinically Discordant Immunoassay Results.

BACKGROUND: Measurement of plasma adrenocorticotropic hormone (ACTH) is key in the differential diagnosis of hypothalamic-pituitary-adrenal disorders. Two-site sandwich immunoassays dominate clinical testing of ACTH in North America; however, discordant results between manufacturers have been repeatedly reported. To resolve the discrepancy, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the intended measurand, biologically active intact ACTH (iACTH). METHODS: The multiple reaction monitoring LC-MS/MS assay was designed to selectively measure full-length iACTH, as well as ACTH analogs and fragments (i.e., ACTH1-24 and ACTH18-39). Epitope assignment of the Roche Elecsys antibodies was performed by MALDI-TOF mass spectrometry. A method comparison between Roche Elecsys and Siemens Immulite ACTH immunoassays was performed and clinically concordant/discordant results identified. In a subset of these samples, the iACTH concentration was determined using the LC-MS/MS method. RESULTS: The lower limit of the measuring interval of the iACTH LC-MS/MS assay was 9 pg/mL (2 pmol/L). The assay was linear from 9 to 1938 pg/mL (2 to 427 pmol/L). Epitope mapping revealed that the Roche capture and detection antibodies bound residues 9-12 and 36-39 of ACTH, respectively. The iACTH LC-MS/MS analysis demonstrated that for discordant results between 2 immunoassays studied, only the Roche results were highly positively correlated with the iACTH concentration. CONCLUSIONS: Immunoprecipitation of biologically active ACTH molecules followed by LC-MS/MS analysis enabled selective detection of iACTH and relevant biologically active fragments in plasma. Applied to the investigation of clinically discrepant results, this method can act as an arbiter of the concentration of iACTH present.

Peritoneal and Pleural Fluid Chemistry Measurements Performed on Three Chemistry Platforms.

BACKGROUND: Chemistry testing is requested for body fluid (BF) specimens despite the lack of assays approved by the US Food and Drug Administration (FDA). The criteria for categorizing fluids as transudate or exudate are not validated across analyzers. OBJECTIVE: To compare BF chemical analysis and classification by different analyzers. METHODS: We analyzed 10 pleural and 18 peritoneal fluids with corresponding plasma specimens using the Vitros 5,1 FS; Abbott ARCHITECT ci8200; and Roche Modular P platforms. Total protein (TP) and lactate dehydrogenase (LDH) were measured for pleural fluids. Light's criteria were applied. Albumin was measured for peritoneal specimens, and the plasma-ascites-albumin gradient was calculated. RESULTS: TP results showed agreement. The Vitros LDH assay produced higher fluid:plasma ratios. Classification by Light's criteria resulted in 1 discrepancy (ARCHITECT). Albumin results showed agreement. There were 2 discrepant gradient interpretations (Vitros). CONCLUSIONS: These data suggest that analyses of pleural and peritoneal fluids using these platforms are diagnostically interchangeable.

Multicenter evaluation of the Access AMH antimüllerian hormone assay for the prediction of antral follicle count and poor ovarian response to controlled ovarian stimulation.

OBJECTIVE: To evaluate a new fully automated antimüllerian hormone (AMH) assay for prediction of poor ovarian response (POR) to ovarian stimulation defined as four or fewer oocytes retrieved. DESIGN: Prospective cohort study. SETTING: Thirteen private and academic fertility centers in the United States. PATIENTS(S): A total of 178 women undergoing their first in vitro fertilization (IVF) cycle eligible for the study were consented and enrolled, with data available from 160 women for prediction of POR and 164 women for AMH correlation with antral follicle count (AFC). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Cutoff point for AMH that predicts POR. Correlation of AMH with AFC, and cutoff point for AMH that correlates with antral follicle count >15. RESULT(S): The mean AMH among the poor responders was 0.74 ng/mL, compared with 3.20 ng/mL for normal to high responders. The AMH cutoff at 90% specificity for predicting POR with the use of the receiver operating characteristic (ROC) curve was 0.93 ng/mL, with an associated sensitivity of 74.1%. For prediction of POR, ROC analysis showed that AMH (area under the ROC curve [AUC] = 0.929) was significantly better than FSH (AUC = 0.615; P<.0001). AMH was positively correlated with AFC (Spearman rho = 0.756). The AMH at 90% sensitivity for AFC >15 was 1.75, with specificity of 59.1%. CONCLUSION(S): A fully automated AMH assay can be a useful biomarker for predicting POR in IVF cycles. Because AMH cutoff points vary depending on the assay used, future studies should continue to calibrate test results to clinically important outcomes.

Does Reverse Triiodothyronine Testing Have Clinical Utility? An Analysis of Practice Variation Based on Order Data from a National Reference Laboratory.

BACKGROUND: Clinical laboratories are under pressure to increase value by improving test utilization. The clinical utility of reverse triiodothyronine (rT3) is controversial. A study was conducted to identify order patterns that might suggest inappropriate utilization of rT3. METHODS: All orders for thyroid tests placed over a period of one year at a national reference laboratory were reviewed. Order patterns by client (hospital) and by provider were analyzed. A Pareto analysis was conducted to determine the percentage of orders placed as a function of the percentage of providers. A systematic review of the indexed literature and an informal review of the web were conducted to identify indications for rT3 testing. RESULTS: There were 402,386 orders for 447,664 thyroid tests, including 91,767 orders for rT3. These orders were placed by 60,733 providers located at 1139 different organizations. Only 20% of providers who ordered thyroid tests placed an order for rT3. Of those who placed an order for rT3, 95% placed two orders or fewer for rT3. One hundred providers (0.1% of the 60,733 providers who placed orders for thyroid tests) accounted for 29.5% of the orders for rT3. Of the 100 providers, 60 with the highest order volumes for rT3 were classified as practitioners of functional medicine. A systematic review of Medline found little evidence to support the high volumes of orders for rT3. A survey of Web sites for functional medicine suggests that rT3 is useful for the diagnosis of rT3 dominance and can be used to direct triiodothyronine replacement therapy. CONCLUSIONS: There is wide practice variation in rT3 testing. A high proportion of tests are ordered by a relatively small proportion of providers. There is little evidence to support high volumes of rT3 testing placed by some practitioners.

Measuring estrogens in women, men, and children: Recent advances 2012-2017.

The measurement of estrogens is important for diagnosing and monitoring the health of women, men, and children. For example, for postmenopausal women or women undergoing treatment for breast cancer with aromatase inhibitors, the measurement of extremely low concentrations of estrogens in serum, especially estradiol, is problematic but essential for proper medical care. Achieving superb analytical sensitivity and specificity has been and continues to be a challenge for the clinical laboratory, but is a challenge that is being taken seriously. Focusing on publications from 2012 to 2017, this review will provide an overview of recent research in the development of methods to accurately and precisely measure estrogens, including a variety of estrogen metabolites. Additionally, the latest in clinical research involving estrogen measurement in women, men, and children will be presented to provide an update on the association of estrogens with diseases or conditions such as breast cancer, precocious puberty, infertility, and pregnancy. This research update will provide context as to why estrogen measurement is important and why laboratories are working hard to support the recommendations made by the Endocrine Society regarding estrogen measurement.

How low can you go? Analytical performance of five automated testosterone immunoassays.

BACKGROUND: Testosterone is commonly measured using immunoassays, yet concerns with the accuracy and quality of testing by these methods exist, particularly for low testosterone concentrations. Study objectives were to evaluate selective performance characteristics, including functional sensitivity (FS), of 5 automated immunoassays for total testosterone. METHODS: FS, imprecision, assay interference, limit of blank, linearity, and accuracy were assessed using the Abbott ARCHITECT i2000SR, SIEMENS ADVIA Centaur and IMMULITE 2000, Beckman Coulter DxI 800, and Roche MODULAR E170. Comparisons to an in-house liquid chromatography-tandem mass spectrometry (LC-MS/MS) method were performed using patient samples from men, women, boys, and girls. RESULTS: FS at 20% coefficient of variation (CV) for the ARCHITECT, Centaur, DxI, E170 and IMMULITE assays were 0.14, 1.23, 0.36, 0.77, 3.49 nmol/L, respectively. Total CVs for the 5-day imprecision study were ≤ 9.0% for all methods. All assays met manufacturer's claims for hemolysis, icterus, and lipemia interference and limit of blank. Dilution linearity studies had deviations from the target recoveries ranging from 3.4% (ARCHITECT) to 14.3% (DxI). Using National Institute of Standards and Technology Standard Reference Material 971, recoveries ranged from 79.2-149.2% (DxI, male and female, respectively). When compared to LC-MS/MS, more immunoassays under-recovered in men and women and over-recovered in boys and girls. Slopes ranged from 0.71 (IMMULITE, women) to 1.35 (DxI, boys). The combined average for percent bias was higher in boys (28.0%) than men (11.6%), women (22.8%), and girls (25.7%). CONCLUSIONS: Challenges with accurately measuring testosterone appear to remain for some immunoassays, but not all. While most immunoassays remain optimized for concentrations observed in healthy men, some showed acceptable performance when challenged at lower concentrations.

The significance of reporting to the thousandths place: Figuring out the laboratory limitations.

OBJECTIVES: A request to report laboratory values to a specific number of decimal places represents a delicate balance between clinical interpretation of a true analytical change versus laboratory understanding of analytical imprecision and significant figures. Prostate specific antigen (PSA) was used as an example to determine if an immunoassay routinely reported to the hundredths decimal place based on significant figure assessment in our laboratory was capable of providing analytically meaningful results when reported to the thousandths places when requested by clinicians. DESIGN AND METHODS: Results of imprecision studies of a representative PSA assay (Roche MODULAR E170) employing two methods of statistical analysis are reported. Sample pools were generated with target values of 0.01 and 0.20 µg/L PSA as determined by the E170. Intra-assay imprecision studies were conducted and the resultant data were analyzed using two independent statistical methods to evaluate reporting limits. RESULTS: These statistical methods indicated reporting results to the thousandths place at the two assessed concentrations was an appropriate reflection of the measurement imprecision for the representative assay. This approach used two independent statistical tests to determine the ability of an analytical system to support a desired reporting level. Importantly, data were generated during a routine intra-assay imprecision study, thus this approach does not require extra data collection by the laboratory. CONCLUSIONS: Independent statistical analysis must be used to determine appropriate significant figure limitations for clinically relevant analytes. Establishing these limits is the responsibility of the laboratory and should be determined prior to providing clinical results.

Multi-Center Benchmark Study Reveals Significant Variation in Thyroid Testing in United States.

BACKGROUND: Studies show that a significant portion of laboratory testing is unnecessary. Thyroid tests are some of the most commonly ordered laboratory tests, yet little is known about practice patterns for laboratory testing for thyroid disease. The objective of this study was to collect data on practice patterns for thyroid testing in the United States. METHODS: A survey was conducted to collect data on annual test volumes for thyroid stimulating hormone (TSH), free thyroxine (FT4), total thyroxine (TT4), free triiodothyronine (FT3), total triiodothyronine (TT3), triiodothyronine uptake (T3U), reverse triiodothyronine (rT3), and complete blood counts (CBC). Sites were also asked to provide data on laboratory utilization management activities. Thyroid workup rates were compared using the TSH/CBC ratio. Thyroid test selection patterns were compared using the ratio of order volumes for thyroid tests relative to TSH. RESULTS: We obtained data from 82 sites. The thyroid workup rate (TSH/CBC) was higher for outpatients (0.26) than for inpatients (0.03). Based on median values, sites ordered 14 FT4, 3 TT4, 4 FT3, 2 TT3, 0.1 rT3, and 0.1 T3U for every 100 TSH orders. The majority (approximately 90%) of orders for T4 were for FT4 rather than TT4. Orders for T3 were almost evenly split between FT3 and TT3. There was significant practice variation in test selection for all tests. The highest variability was for the rT3/TSH and T3U/TSH ratios. Most organizations reported at least some laboratory utilization management activities. There was a weak relationship between utilization management initiatives and the quality of orders for thyroid tests. CONCLUSIONS: There is considerable practice variation in thyroid testing which suggests a need for better guidance in test selection. Based on our sample, some organizations could significantly improve the quality of thyroid testing and reduce testing costs.

Thyroglobulin Antibody Screen Prior to Mass Spectrometry Provides Measurable Cost Savings and Optimal Laboratory Utilization.

OBJECTIVES: Liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods that allow accurate quantitation of thyroglobulin (Tg) in the presence of Tg antibodies (TgAbs) have recently become available. Due to cost differences between LC-MS/MS and immunoassay, some laboratories now offer a reflex test strategy that uses LC-MS/MS only for TgAb-positive samples. The goal of this study was to examine utilization of Tg testing strategies and cost savings. METHODS: Test ordering patterns were examined for over 150,000 orders for TgAb and Tg in our laboratory. The average list price was determined from three separate commercial laboratories offering this testing. RESULTS: Data showed that 89% of orders for Tg used the reflex test option, resulting in a savings of over $3 million compared with testing all samples by LC-MS/MS. Of the Tg by LC-MS/MS orders not using the reflex option, 1,663 also included a separate order for TgAb on the same patient sample, representing approximately $170,000 in potentially unnecessary costs from TgAb-negative samples. CONCLUSIONS: Identifying situations to use more expensive testing methods (eg, LC-MS/MS) only when necessary, such as for TgAb-positive patients, leads to considerable cost savings and a more economical use of valuable health care resources.

Antimüllerian Hormone Levels Are Not Altered by Glucose Challenge or a Meal.

BACKGROUND: Measurement of antimüllerian hormone (AMH) is used to assess ovarian reserve. Circulating levels of AMH correlate with antral follicle count, with relatively high levels indicating an ample reserve of primary and preantral follicles in the ovary. AMH levels are stable with dilution and freezer storage, and are not altered by hemolysis or menstrual cycle day in young women of reproductive age. We sought to examine whether glucose challenge or food intake modifies AMH levels compared with fasting. METHODS: Residual plasma samples were available from 54 pregnant women under fasting conditions and then 1, 2, and 3 h after ingestion of a 100-g glucose challenge. These samples were collected as part of routine clinical care to identify gestational diabetes (GDM) at 24-28 weeks of gestation. Twelve of these women met criteria for GDM based on an increased glucose level at a minimum of 2 time points. A second set consisted of serum samples collected from 8 nonpregnant women at fasting and 1 h after a meal. Levels of AMH were measured using an ultrasensitive assay (Ansh Labs, Webster, TX). A 2-way ANOVA (sample timing and GDM status) or matched t-test was performed. AMH measurements were subject to a logarithmic transformation before analysis. RESULTS: Median AMH levels in pregnant women at 1, 2, or 3 h after glucose challenge did not differ compared with AMH levels at fasting or by diagnosis of GDM. Similarly, there was no difference in median AMH levels in nonpregnant women of reproductive age at fasting and after a meal. CONCLUSION: AMH levels are not altered by glucose or food intake.

Comparative analysis of neutrophil gelatinase-associated lipocalin and other laboratory markers for lupus nephritis: a cross-sectional investigation.

Background Lupus nephritis is one of the most serious complications of systemic lupus erythematosus. This study evaluates the prevalence and correlation between neutrophil gelatinase-associated lipocalin and other biomarkers associated with renal involvement in systemic lupus erythematosus. Methods Paired serum and urine specimens from 50 suspected systemic lupus erythematosus patients, characterized by antinuclear antibodies detected by indirect immunofluorescence assay and varying positive concentrations of anti-double stranded DNA antibodies by Crithidia luciliae immunofluorescence assay, were investigated. Of these 50 patients, 18 were identified with renal involvement based upon laboratory serology. Patients and healthy control serum samples ( n = 50) were also evaluated for high avidity double stranded DNA IgG antibodies, anti-C1q IgG antibodies, and serum creatinine. The prevalence and relationship between biomarkers were evaluated using statistical methods. Results Serum and urine neutrophil gelatinase-associated lipocalin concentrations were significantly elevated in patients compared to controls, with a prevalence of 24% and 36%, respectively. These concentrations were also more markedly increased in systemic lupus erythematosus patients with renal involvement than those without. Spearman's correlations between neutrophil gelatinase-associated lipocalin and other biomarkers tested ranged from 0.06 to 0.66 in all patients. Combined concordance as determined by Cronbach alpha coefficient between biomarkers was reduced from 0.71 to 0.58 (serum) and 0.62 (urine) when neutrophil gelatinase-associated lipocalin was removed. Conclusions Neutrophil gelatinase-associated lipocalin concentrations are elevated and demonstrate variable associated with other laboratory markers for renal involvement in systemic lupus erythematosus. Prospective longitudinal studies are needed to determine the optimal biomarker combinations for use in routine management of systemic lupus erythematosus patients at-risk for lupus nephritis.

Pediatric Reference Intervals for Free Thyroxine and Free Triiodothyronine by Equilibrium Dialysis-Liquid Chromatography-Tandem Mass Spectrometry.

OBJECTIVE: Thyroid hormone concentrations fluctuate during growth and development. To accurately diagnose thyroid disease in pediatric patients, reference intervals (RIs) should be established with appropriate age groups from an adequate number of healthy subjects using the most exact methods possible. Obtaining statistically useful numbers of healthy patients is particularly challenging for pediatric populations. The objective of this study was to determine non-parametric RIs for free thyroxine (fT4) and free triiodothyronine (fT3) using equilibrium dialysis-high performance liquid chromatography-tandem mass spectrometry with over 2200 healthy children 6 months-17 years of age. METHODS: Subjects were negative for both thyroglobulin and thyroid peroxidase autoantibodies and had normal thyrotropin concentrations. The study included 2213 children (1129 boys and 1084 girls), with at least 120 subjects (average of 125) from each year of life, except for the 6 month to 1 year age group (n=96). RESULTS: Non-parametric RIs (95th percentile) for fT4 were: 18.0-34.7 pmol/L (boys and girls, 6 months-6 years) and 14.2-25.7 pmol/L (boys and girls, 7-17 years). RIs for fT3 were: 5.8-13.1 pmol/L (girls, 6 months-6 years); 5.7-11.8 pmol/L (boys, 6 months-6 years); 5.7-10.0 pmol/L (boys and girls, 7-12 years); 4.5-8.6 pmol/L (girls, 13-17 years); and 5.2-9.4 pmol/L (boys, 13-17 years). CONCLUSION: Numerous significant differences were observed between pediatric age groups and previously established adult ranges. This emphasizes the need for well-characterized RIs for thyroid hormones in the pediatric population.