Case report: When measured free T4 and free T3 may be misleading. Interference with free thyroid hormones measurements on Roche® and Siemens® platforms

High prevalence of thyroid hormone autoantibody and low rate of thyroid hormone detection interference

Objective

Thyroid hormone autoantibody (THAb) is a common antibody in autoimmune disease and can interfere with the detection of thyroid hormone (TH). There was no research reporting the prevalence of THAb in Chinese and the rate of THAb interfering with TH detection.

Methods

We collected 114 patients with autoimmune thyroid disease (AITD) (Hashimoto's thyroiditis, 57 cases; Graves’ disease, 57 cases), 106 patients with nonthyroid autoimmune diseases (NTAID), and 120 healthy subjects. According to the presence or absence of thyroid antibodies, patients with NTAID were divided into two groups: NTAID‐AITD and NTAID groups. Radioimmunoprecipitation technique was used to detect THAb in all subjects. TH was detected on Abbot and Roche platforms in patients with positive THAb.

Results

The prevalence of THAb was 22.8% in Hashimoto's thyroiditis and 45.6% in Graves’ disease. The prevalence of THAb in AITD group was lower than that in NTAID or NTAID‐AITD groups (34.2% vs. 61.5%, p = 0.014; 34.2% vs. 71.3%, p < 0.01). Among total 98 patients with positive THAb, TH levels of 9 patients were falsely elevated (9.18%).

Conclusion

The prevalence of THAb in AITD patients was lower than that in NTAID patients. Although THAb had a high frequency in various autoimmune diseases, the prevalence of THAb interfering with TH detection was only 9.18%.

Adequate timing and constant supervision are the keys for successful implementation of levothyroxine or levothyroxine/paracetamol absorption test

Background

Levothyroxine (LT₄) pseudomalabsorption due to medication non-adherence results in significant costs for Health Service. High dose LT₄ or LT₄/paracetamol absorption test is used in such cases. Hence, establishment of an optimal test protocol and timing of sample collection is of utmost importance.

Case presentation

A 34-year old woman was admitted to our Department because of severe hypothyroidism [on admission thyrotropin (TSH) > 100 μIU/ml, free thyroxine (FT₄) 0.13 ng/dl (ref. range 0.93–1.7)] despite apparently taking 1000 μg of LT₄ a day. Autoimmune hypothyroidism had been diagnosed 4 years before during post-partum thyroiditis. Subsequently, it was not possible to control her hypothyroidism despite several admissions to two University Hospitals and despite vehement denial of compliance problems. There was no evidence of coeliac disease or other malabsorption problems, though gluten-free and lactose-free diet was empirically instigated without success. A combined paracetamol (1000 mg)/LT₄ (1000 μg) absorption test was performed in one of these Hospitals. This showed good paracetamol absorption (from < 2 μg/ml to 14.11 μg/ml at 120 min), with inadequate LT₄ absorption (FT₄ increase from 5.95 pmol/l to 9.92 pmol/l at 0 and 120 min respectively). About 2 years prior to admission to our Department the patient was treated with escalating doses of levothyroxine [up to 3000 μg of T₄ and 40 μg of triiodothyronine (T₃) daily] without significant impact on TSH (still > 75 μIU/ml, and FT₄ still below reference range).

After admission to our Department we performed a 2500 μg LT₄ absorption test with controlled ingestion of crushed tablets, strict patient monitoring and sampling at 30 min intervals. We observed a quick and striking increase in FT₄ from 0.13 to 0.46, 1.78, 3.05 and 3.81 ng/dl, at 0, 30, 60, 90 and 120 min, respectively. Her TSH concentration decreased to 13.77 μIU/ml within 4 days. When informed, that we had managed to “overcome” her absorption problems, she discharged herself against medical advice and declined psychiatric consultation.

Conclusions

Adequate patient supervision and frequent sampling (e.g. every 30 min for 210 min) is the key for successful implementation of LT₄ absorption test. Paracetamol coadministration appears superfluous in such cases.

Falsely undetectable TSH in a euthyroid patient

Background

Measuring thyroid hormone levels is essential and helpful in the diagnosis of thyroid diseases.

Case presentation

We had a patient with undetectable serum TSH level by the Siemens immunoassay, whereas by ELISA and Roche-Abott immunoassay, serum level of TSH was in the normal range.

Conclusion

If the result of TSH level revealed very low or undetectable through one specific method, it should not be considered necessarily as a symptom of hyperthyroidism. It is to be requested to measure by the other methods with other devices too.

Heterophile antibody interference affecting multiple Roche immunoassays: A case study

BACKGROUND

Analysis of many clinically important analytes is dependent on antibody-based assays. However, depending on the design, these assays are vulnerable to interference from endogenous molecules including circulating antibodies and free biotin. In this case report, we describe a patient whose laboratory findings from immunoassay based methodologies, are inconsistent with the clinical presentation.

CASE PRESENTATION

A 14-year-old male was referred to Pediatric Endocrinology for suspected hyperthyroidism based on critically elevated free thyroxine (fT4) levels although clinical assessment was inconsistent with hyperthyroidism. Because repeat testing was discrepant, Endocrinology questioned the validity of the results prompting consultation with the laboratory to investigate the source of the inconsistent findings. Review of discordant results revealed that fT4 levels measured in laboratories utilizing Roche instrumentation were critically high, while results from laboratories using alternative platforms (i.e. Siemens Centaur) were within normal limits.

CONCLUSION

After a comprehensive evaluation which included testing of paired specimens on multiple platforms, measurement of serially diluted specimens and a formal evaluation for the presence of heterophile antibodies, it was determined that a heterophile antibody interference was the most likely cause of the aberrant results in this patient.

Irregular analytical errors in diagnostic testing - a novel concept

BACKGROUND

In laboratory medicine, routine periodic analyses for internal and external quality control measurements interpreted by statistical methods are mandatory for batch clearance. Data analysis of these process-oriented measurements allows for insight into random analytical variation and systematic calibration bias over time. However, in such a setting, any individual sample is not under individual quality control. The quality control measurements act only at the batch level. Quantitative or qualitative data derived for many effects and interferences associated with an individual diagnostic sample can compromise any analyte. It is obvious that a process for a quality-control-sample-based approach of quality assurance is not sensitive to such errors.

CONTENT

To address the potential causes and nature of such analytical interference in individual samples more systematically, we suggest the introduction of a new term called the irregular (individual) analytical error. Practically, this term can be applied in any analytical assay that is traceable to a reference measurement system. For an individual sample an irregular analytical error is defined as an inaccuracy (which is the deviation from a reference measurement procedure result) of a test result that is so high it cannot be explained by measurement uncertainty of the utilized routine assay operating within the accepted limitations of the associated process quality control measurements.

SUMMARY

The deviation can be defined as the linear combination of the process measurement uncertainty and the method bias for the reference measurement system. Such errors should be coined irregular analytical errors of the individual sample. The measurement result is compromised either by an irregular effect associated with the individual composition (matrix) of the sample or an individual single sample associated processing error in the analytical process.

OUTLOOK

Currently, the availability of reference measurement procedures is still highly limited, but LC-isotope-dilution mass spectrometry methods are increasingly used for pre-market validation of routine diagnostic assays (these tests also involve substantial sets of clinical validation samples). Based on this definition/terminology, we list recognized causes of irregular analytical error as a risk catalog for clinical chemistry in this article. These issues include reproducible individual analytical errors (e.g. caused by anti-reagent antibodies) and non-reproducible, sporadic errors (e.g. errors due to incorrect pipetting volume due to air bubbles in a sample), which can both lead to inaccurate results and risks for patients.

Diagnostic Dilemma in Discordant Thyroid Function Tests Due to Thyroid Hormone Autoantibodies

OBJECTIVE

Assay interference could be the cause of abnormal thyroid function tests. Early recognition prevents inappropriate patient management. The objective of this report is to present a case with discordant thyroid function tests in different thyroid assay platforms due to thyroid autoantibodies.

METHODS

We present a case her family, laboratory data and methods that investigate immunoassay interference.

RESULTS

A 21-year-old woman with autoimmune thyroid disease was treated for hypothyroidism with levothyroxine and noted to have elevated total and free thyroxine, free triiodothyronine but normal thyroid-stimulating hormone. Repeat thyroid function tests using different platforms revealed discrepant results. Further investigation showed that the patient had positive thyroid hormone autoantibodies (THAAbs).

CONCLUSION

We demonstrates abnormal thyroid function tests caused by THAAbs. The latter were the cause of interference with assays resulting in discrepant test results inconsistent with the clinical presentation. Early recognition would prevent inappropriate patient management.

Pseudohyperthyroxinemia in a hypothyroid patient secondary to chronic phlegmon

Background: Elevated free thyroxine could be primary or secondary, endogenous or exogenous and often presents with symptoms of hyperthyroidism. Thyroxine levels are low in hypothyroidism, where the individual requires exogenous supplementation to maintain a euthyroid state. However, thyroxine levels may be elevated in a hypothyroid patient because of over-supplementation/over-suppression with exogenous agent(s) or secondary to other pathologies and rarely, laboratory error or assay interference may cause alteration in the levels of the thyroid hormones.

Case report: A 44-year-old man with well controlled hypothyroidism was referred for assessment of markedly elevated TSH and free thyroxine levels with low free T3. Clinically the patient was hypothyroid with symptoms of fatigue and weight gain of 30 pounds over the past 3-months and the TSH levels were consistent with marked hypothyroidism. However, free thyrxoine was markedly elevated, opposite of what to be expected. A systematic evaluation, presented here, was helpful in the diagnosis of pseudohyperthyroxinemia secondary to assay interferences in a timely fashion, avoiding unnecessary further investigations.

Conclusions: Interference in immunoassays is an important clinical problem that is underestimated and can have important clinical consequences. It is important to recognize the possibility of such interferences early in the diagnostic process and to implement protocols to identify these whenever possible, in a timely fashion, to prevent untoward consequences. Vigilance by both the clinician and the laboratory staff is important.

Clinical evaluation of various thyroid hormones on thyroid function

To clarify the clinical value of serums total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), and free thyroxine (FT4) and provide a more eligible and economic strategy to assess thyroid function. A total of 2,673 participants (500 patients with hyperthyroidism, 500 patients with hypothyroidism, and 1,673 healthy people) were involved in our study. Serums TT3, TT4, FT3, and FT4 and thyrotropin (TSH) were measured with VIDAS fluorescent enzyme immunoassay. The Pearson correlation between TT3, TT4, FT3, and FT4 and TSH was determined to identify the most important indicator for thyroid function besides TSH. The correlation of TT4, and FT4 with TSH was statistically significant in healthy individuals (P < 0.01), and the R-values were -0.065 and -0.152, respectively. The correlation of TT4, FT4, TT3, and FT3 with TSH was statistically significant in patients with hyperthyroidism, and the R-values were -0.241, -0.225, -0.195, and -0.176, respectively. The correlation of TT4, FT4, TT3, and FT3 with TSH was statistically significant in patients with hypothyroidism, and the R-values were -0.322, -0.262, -0.179, and -0.136, respectively. In our opinion, TSH and FT4 are the most valuable indicators in assessing thyroid function in a healthy population, and TSH and TT4 are the most meaningful in hyperthyroidism and hypothyroidism.