Thyroid stimulating hormone (TSH) EQA results: why they fail and what to check.
What is known to go wrong with thyroid stimulating hormone (TSH) in external quality assurance, how each problem shows itself in the results, and the checks to make, with every source listed. This is the thyroid stimulating hormone (TSH) monograph EQAWarden ships with. First check: Confirm the method code (TSH3ULII or TSH3-UL) in myQAP matches the assay each analyser runs, and compare with that Atellica peer group, not the all-method mean.
The limits, units and methods behind every thyroid stimulating hormone (TSH) result.
| RCPAQAP APS, General Serum Chemistry (GSC) | ±0.1 mIU/L up to 0.5 mIU/L, ±20% above |
|---|---|
| Units | mIU/L. 1 µIU/mL = 1 mIU/L |
| Methods | Third-generation two-site sandwich chemiluminescent immunoassay (acridinium ester label; FITC-labelled capture antibody on anti-fluorescein paramagnetic particles), direct RLU: Atellica IM TSH3ULII and TSH3-UL (confidence: High)[1, 2] Other sandwich immunoassays (electrochemiluminescence, chemiluminescent microparticle) on other platforms, each calibrated to a WHO international standard (confidence: High)[4] |
| Standardisation | No reference measurement procedure; methods are calibrated to WHO international standards and differ in results. The IFCC C-STFT showed that harmonisation of TSH by recalibration against an all-procedure trimmed mean is feasible[4, 5]. Both Atellica assays state traceability to the WHO 3rd IRP for human TSH 81/565[1, 2]; the IFU does not mention the C-STFT harmonisation. The fair EQA comparator is the Atellica method group. |
| Expected error mode | Proportional. Calibration and lot effects are proportional; near the lower limit the error is dominated by a constant component. |
| Biological variation | Within-subject CV 17.82% and between-subject CV 36.04%, from the EFLM database (meta-analysis, 7 studies). |
| Desirable performance | Imprecision 8.91%, bias 10.05%, total allowable error 24.75%, derived from biological variation (Fraser). |
Platform details are for the Siemens Atellica, the platform EQAWarden's first release covers. Other platforms differ: check your own instructions for use.
9 ways a thyroid stimulating hormone (TSH) result goes wrong in EQA, and how to tell them apart.
Method-group target and commutability of the EQA material
Why it happens. Immunoassays for this measurand are not harmonised: calibration traceability, antibodies and the handling of processed (lyophilised, pooled or spiked) material differ between methods, so differences between method groups in EQA material may not exist in patient samples. TSH is calibrated to WHO standards in every major method, yet between-method differences persist[5].
Direction. method-specific
How it shows. method-group, persistent; the Atellica peer group as a whole sits away from the all-method or reference target
Check. Compare the result with the Siemens Atellica method group; if the laboratory agrees with its peers but not with the all-method target, treat it as a method difference, not a laboratory fault.
TSH3-UL and TSH3ULII are different assays
Why it happens. The TSH3ULII IFU compares TSH3ULII (y) with Atellica TSH3-UL (x): y = 0.97x - 0.006 µIU/mL (n = 323). TSH3ULII therefore reads about 3% below TSH3-UL on patient serum. A laboratory that changes version, or runs one version per analyser, or is enrolled in the wrong method code, carries that difference.
Direction. either: negative (about 3%) for TSH3ULII against a TSH3-UL peer group; positive in the reverse case
How it shows. method-group, step, proportional; begins when the assay version changed
Check. Confirm which TSH assay each analyser runs (confirm in the laboratory's Atellica documentation) and that the myQAP method code matches it; look for a step at the version change date.
New reagent lot and its master curve (TSH3ULII or TSH3-UL)
Why it happens. Each Atellica IM reagent lot carries a lot-specific master curve read from 2D barcodes; a new lot needs a new two-point calibration. Intervals in the IFU: lot calibration 63 days, pack calibration 63 days, onboard stability 63 days. In the TSH3ULII reproducibility study the between-lot CV was 1.5% to 3.7% depending on level; a new pack of an already calibrated lot needs no new calibration. A lot-to-lot difference that the two-point calibration does not correct shifts results on every analyser using that lot. The size of the shift can differ between patient samples and EQA or control material.
Direction. either (sign set by the lot difference)
How it shows. step, proportional, persistent; begins at the date the new reagent lot was first used and follows that lot
Check. Pull the reagent and calibrator lot history for the analysis date; compare IQC before and after the lot change and, if available, run the master curve material or a retained EQA sample on both lots.
Two-point recalibration or calibrator handling (TSH3ULII, CAL 3A (kit calibrator))
Why it happens. Atellica IM two-point calibration adjusts the lot master curve with a low and a high calibrator. The kit calibrator is lyophilised (2.0 mL), stable 28 days at 2-8 C once reconstituted and only 4 hours at room temperature on the system, and may only be used with reagent of the same kit lot; the TSH3-UL IFU also warns against pouring calibrator back or topping up cups. A reconstitution volume error, an evaporated or out-of-date reconstituted calibrator, or a calibrator from the wrong lot shifts every result after that calibration on that analyser. The TSH3ULII master curve material (4 levels) can check a calibration without calibrating.
Direction. either
How it shows. step, proportional, instrument-specific; starts at a dated calibration on one analyser
Check. Open the calibration record for the run (date, calibrator lot, reconstitution date, calibration acceptance); compare IQC before and after; compare with a second analyser calibrated separately.
Chemiluminescent signal or wash fault in a sandwich assay
Why it happens. The assay is a two-site sandwich with a direct relationship between analyte and relative light units (RLU). A loss of signal (trigger reagents, luminometer, particle loss at washing) reads low, while poor washing of unbound label reads high; competitive assays on the same analyser move the opposite way.
Direction. either: negative for a loss of signal; positive for residual unbound label
How it shows. instrument-specific, survey-wide, analyte-group:im_sandwich; sandwich assays move one way and competitive assays the other on the same analyser
Check. Check whether other Atellica IM sandwich assays on the same analyser moved in the same direction and competitive assays in the opposite direction; review trigger reagent and wash fluid onboard times, luminometer checks and maintenance logs.
Measuring range, onboard dilution and hook
Why it happens. Measuring interval 0.008-150 mIU/L (IFU); above 150 the sample is diluted onboard 1:2 or 1:5 with Multi-Diluent 15 (onboard 7 days once opened). TSH3-UL onboard dilutions recovered 94-100% on average. Samples up to 3000 mIU/L still report above 150 (no hook within that range).
Direction. either
How it shows. single, concentration-dependent; only a sample above 150 mIU/L
Check. For a high TSH EQA sample, check the above-range flag, the dilution factor applied and entered, and the onboard age of Multi-Diluent 15.
Low-TSH samples and the lower limit
Why it happens. TSH3ULII LoQ 0.004 mIU/L with within-lab CV 2.1-3.2% down to 0.086 mIU/L; the assay chart (11314389 Rev 05) lists a lower limit of 0.010 while the later IFU Rev 04 lists 0.008. Relative scatter rises near the lower limit.
Direction. either
How it shows. concentration-dependent, single; a constant offset of a few thousandths of a mIU/L near the lower limit
Check. Judge a low-TSH EQA sample against the absolute part of the APS, not only the percentage; check the lower limit set in the laboratory's test definition.
Heterophile or human anti-animal antibodies
Why it happens. The IFU says the assay is designed to minimise heterophilic antibody interference but that such antibodies can still give falsely high or low results. The capture uses FITC and anti-fluorescein, not streptavidin-biotin; biotin 0.35 mg/dL (14.3 µmol/L) gave 10% bias or less. Fluorescein from retinal angiography above 0.24 µg/mL lowers TSH (patient samples only). These antibodies belong to individual donors; a pooled EQA material is unlikely to carry them at an effective level unless it comes from a single donor.
Direction. either
How it shows. single, sample-specific; one sample reads off in one method group and not in others
Check. If a single-donor EQA sample is off in the Atellica group only, ask RCPAQAP about the material source; retest after a heterophile blocking step or on another platform if the laboratory keeps the sample.
Test definition update left operator-defined parameters unchanged
Why it happens. Siemens issues new Atellica IM test definition versions (for TSH3-UL, test definition 1.4 raised the lot calibration interval from 49 to 63 days). Operator-defined parameters are not updated automatically when a test definition is installed, so a dilution point, unit or conversion factor set by the laboratory can differ from the new default.
Direction. either
How it shows. step, instrument-specific; starts at the software or test definition update
Check. Compare the installed test definition version and operator-defined parameters on each analyser with the current assay chart and the enhancement notice; check the date of the last test definition installation.
The checks, in order.
- Confirm the method code (TSH3ULII or TSH3-UL) in myQAP matches the assay each analyser runs, and compare with that Atellica peer group, not the all-method mean.
- Check for a reagent lot change or recalibration (lot and pack interval 63 days) near the analysis date; review IQC and, if needed, the TSH3ULII master curve material.
- For a high sample, check above-range flags, dilution factor and Multi-Diluent 15 onboard age; for a low sample, compare the absolute difference with the APS absolute limit.
- If several IM sandwich assays on one analyser are low (or competitive assays high) together, review trigger reagents, wash and luminometer records.
- Check units (mIU/L and µIU/mL are numerically equal) and any correlation factor in CentraLink or the LIS.
Unit traps
- mIU/L and µIU/mL are numerically identical (factor 1); a ratio of 1000 suggests mU/L entered as µU/L or similar.
EQAWarden runs these checks as rules on every survey, ranks the likely causes with their evidence, and the reviewer decides. All analytes · The 58 rules · The whole knowledge base · How an EQA investigation runs
Questions about thyroid stimulating hormone (TSH) EQA.
What is the RCPAQAP allowable performance specification for thyroid stimulating hormone (TSH)?
In the General Serum Chemistry (GSC) programme it is ±0.1 mIU/L up to 0.5 mIU/L, ±20% above, evaluated at the target. RCPAQAP can change its specifications, so confirm the current table at each enrolment year.
What is a common cause of a failed thyroid stimulating hormone (TSH) EQA result?
Method-group target and commutability of the EQA material. Immunoassays for this measurand are not harmonised: calibration traceability, antibodies and the handling of processed (lyophilised, pooled or spiked) material differ between methods, so differences between method groups in EQA material may not exist in patient samples. TSH is calibrated to WHO standards in every major method, yet between-method differences persist.
What should be checked first when a thyroid stimulating hormone (TSH) EQA result fails?
Confirm the method code (TSH3ULII or TSH3-UL) in myQAP matches the assay each analyser runs, and compare with that Atellica peer group, not the all-method mean.
How are thyroid stimulating hormone (TSH) units converted?
1 µIU/mL = 1 mIU/L.
Where every fact on this page came from.
- Siemens Healthineers. Atellica IM TSH3-Ultra II (TSH3ULII) [OUS], Instructions for Use, part 11208609 Rev. 04, 2026-07. Siemens Document Library id 1180848.
- Siemens Healthineers. Atellica IM TSH3-UL Instructions for Use, 10995434_EN Rev. 04, 2021-03. https://content.doclib.siemens-healthineers.com/rest/v1/view?document-id=784005
- Siemens Healthineers. Atellica IM TSH3ULII Master Curve Material, Instructions for Use, part 11208606 Rev. 02, 2024-07. Siemens Document Library id 1061380.
- Thienpont LM, Van Uytfanghe K, Beastall G, et al. Report of the IFCC Working Group for Standardization of Thyroid Function Tests; part 1: thyroid-stimulating hormone. Clin Chem 2010;56:902-911.
- Thienpont LM, Van Uytfanghe K, De Grande LAC, et al. Harmonization of serum thyroid-stimulating hormone measurements paves the way for the adoption of a more uniform reference interval. Clin Chem 2017;63:1248-1260.
- Siemens Healthineers. Atellica Solution IM Assay Chart, part 11314389 Rev. 05, 2025-12. Siemens Document Library id 1151608. https://content.doclib.siemens-healthineers.com/rest/v1/view?document-id=1151608
- JCTLM Database of higher-order reference materials, measurement methods/procedures and services (queried 2026-09-28 via the public search API https://www.jctlmdb.org/backend/api/jctlm/searchRmp|searchRm|searchRms). https://www.jctlmdb.org/
- Miller WG, Jones GRD, Horowitz GL, Weykamp C. Proficiency testing/external quality assessment: current challenges and future directions. Clin Chem 2011;57:1670-80. doi:10.1373/clinchem.2011.168641
- Badrick T, Miller WG, Panteghini M, Delatour V, Berghall H, MacKenzie F, Jones G. Interpreting EQA - understanding why commutability of materials matters. Clin Chem 2022;68:494-500. doi:10.1093/clinchem/hvac002
- Siemens Healthineers. Atellica Solution Operator's Guide, software version 1.31, part 11069101 Rev. 13, 2025-10.
- Miller WG, Erek A, Cunningham TD, Oladipo O, Scott MG, Johnson RE. Commutability limitations influence quality control results with different reagent lots. Clin Chem 2011;57:76-83. doi:10.1373/clinchem.2010.148106
- Wild D (ed.). The Immunoassay Handbook: Theory and Applications of Enzyme Immunoassay, Electrochemiluminescence and Related Techniques. 4th ed. Oxford: Elsevier; 2013. Cited as textbook knowledge for competitive versus sandwich signal-response relationships; not re-read in this review.
- Jassam N, Jones CM, Briscoe T, Horner JH. The hook effect: a need for constant vigilance. Ann Clin Biochem 2006;43:314-317. doi:10.1258/000456306777695726
- Kricka LJ. Human anti-animal antibody interferences in immunological assays. Clin Chem 1999;45:942-956.
- Tate J, Ward G. Interferences in immunoassay. Clin Biochem Rev 2004;25:105-120 (AACB journal). https://pmc.ncbi.nlm.nih.gov/articles/PMC1904417/
- Siemens Healthineers. Atellica IM Analyzer Test Definition Enhancements, Customer Information, part 11314997 Rev. 17, 2026-05. Siemens Document Library id 1173692. https://content.doclib.siemens-healthineers.com/rest/v1/view?document-id=1173692
- EFLM Biological Variation Database (Aarsand AK et al., EFLM WG-BV). https://biologicalvariation.eu/ - meta-analysis values read from https://biologicalvariation.eu/api/meta_calculations and individual studies from https://biologicalvariation.eu/api/bv_specifications, retrieved 2026-09-28. https://biologicalvariation.eu/
- Fraser CG. Biological Variation: From Principles to Practice. Washington DC: AACC Press; 2001 (textbook; formulae desirable CVa<=0.5CVi, bias<=0.25*sqrt(CVi^2+CVg^2), TEa=1.65*CVa+bias).
- RCPAQAP. Chemical Pathology Analytical Performance Specifications (web page; dateModified 2025-03-05). https://rcpaqap.com.au/resources/chemical-pathology-analytical-performance-specifications/
See EQAWarden review a thyroid stimulating hormone (TSH) result.
Twenty minutes on a video call, on a fictional demo year: the score, the findings, the ranked causes and the signed review.