False hyperthyroidism caused by interference in immunoassays

ObjectivesImmunoassays used to assess thyroid function are vulnerable to different types of interference that may affect clinical decision-making.Case presentationWe report the case of a 37-year-old woman who developed iatrogenic hypothyroidism after having received radioiode therapy who visited our hospital for her annual checkup. The patient was asymptomatic, without signs suggestive of thyroid disease. However, laboratory analysis proved otherwise: thyrotropin (TSH) 7.75 mU/L, thyroxine (FT4) >7.7 ng/dL.ConclusionsThe inconsistency between her clinical symptoms and the biochemistry data raised the possibility of a methodological interference. A thorough evaluation of the main causes of interference was conducted in the laboratory to exclude the presence of interference in TSH and FT4. Finally, different interfering agents were identified, which affected free thyroid hormone and TSH determination.

Familial dysalbuminaemic hyperthyroxinaemia interferes with current free thyroid hormone immunoassay methods

Objective Familial dysalbuminaemic hyperthyroxinaemia (FDH), most commonly due to an Arginine to Histidine mutation at residue 218 (R218H) in the albumin gene, causes artefactual elevation of free thyroid hormones in euthyroid individuals. We have evaluated the susceptibility of most current free thyroid hormone immunoassay methods used in the United Kingdom, Europe and Far East to interference by R218H FDH. Methods Different, one- and two-step immunoassay methods were tested, measuring free T4 (FT4) and free T3 (FT3) in 37 individuals with genetically proven R218H FDH. Results With the exception of Ortho VITROS, FT4 measurements were raised in all assays, with greatest to lowest susceptibility to interference being Beckman ACCESS > Roche ELECSYS > FUJIREBIO Lumipulse > Siemens CENTAUR > Abbott ARCHITECT > Perkin-Elmer DELFIA. Five different assays recorded high FT3 levels, with the Siemens CENTAUR method measuring high FT3 values in up to 30% of cases. However, depending on the assay method, FT4 measurements were unexpectedly normal in some, genetically confirmed, affected relatives of index FDH cases. Conclusions All FT4 immunoassays evaluated are prone to interference by R218H FDH, with their varying susceptibility not being related to assay architecture but likely due to differing assay conditions or buffer composition. Added susceptibility of many FT3 assays to measurement interference, resulting in high FT4 and FT3 with non-suppressed TSH levels, raises the possibility of R218H FDH being misdiagnosed as resistance to thyroid hormone beta or TSH-secreting pituitary tumour, potentially leading to unnecessary investigation and inappropriate treatment.

Determinants of deranged thyroid function parameters in children admitted for management of diabetic ketoacidosis

Background: Sick euthyroid syndrome is frequent in children admitted with diabetic ketoacidosis (DKA). This study evaluates the interplay of various metabolic factors with occurrence of deranged thyroid function tests in children admitted for management of DKA.Methods: 194 children admitted for management of DKA were selected from hospital records. Children on thyroxine replacement or those with overt hypothyroidism or anti-TPO antibody positive were excluded. Tests for liver function, renal function, lipid profile, serum osmolarity, thyroid function, c-peptide levels, and glycosylated hemoglobin were done for all. Children were divided into a euthyroid group (n=88) and an euthyroid sick syndrome（ESS）group (n=106).Results:The ESS group had a higher WBC, PG, β-HB, TG, AG, and HbA1c and lower HCO3-, PA, and ALB levels compared with the euthyroid group (P<0.05). FT3 levels were significantly correlated to β-HB, HCO3-, AG, PA, and HbA1c. (r=-0.642, 0.681, -0.377, 0.581, -0.309, respectively; P<0.01) FT4 levels were significantly correlated to β-HB, HCO3-, and ALB levels (r=-0.489, 0.338, 0.529, respectively; P<0.01). TSH levels were significantly affected by HCO3– only (r=-0.28; P<0.01). HCO3– level was the most important factor deciding adjudication to euthyroid or ESS group on logistic regression analysis (OR=0.844, P=0.004, 95%CI=0.751­-0.948).Conclusions: Lower levels of free thyroid hormones and occurrence of ESS is associated with a higher degree of acidosis in children admitted with DKA. Lower levels of markers of nutrition such as serum albumin and pre-albumin levels are associated with lower levels of free thyroid hormone concentrations in children with DKA.

SUN-515 Use of Plasmapheresis for Treatment of Thyroid Storm Resistant to Antithyroidals

Management strategies of thyroid storm include measures to reduce thyroid hormone synthesis, hormone release, conversion from T4 to T3, and inhibition of the peripheral effects of excessive thyroid hormone. Plasmapheresis has been described as a treatment option when traditional therapy is not successful or not feasible. We present a case of an adult patient who presented in thyroid storm in whom plasmapheresis was used successfully as a bridge to thyroidectomy. 51-year-old female with history of hypertension presented with sudden onset shortness of breath, and palpitations. She had an irregular heart rate of 140BPM, respiratory rate of 40, mean arterial blood pressure 65mmHg. Electrocardiogram confirmed atrial fibrillation with rapid ventricular response and the patient was admitted to the intensive care unit. She was started on diltiazem drip and subsequently received amiodarone and electrical cardioversion due to persistent rapid heart rate. She developed respiratory distress and required endotracheal intubation. Initial thyroid profile revealed low TSH and normal FreeT4, but her FT4 increased above normal on day 2, treatment for thyroid storm was initiated with potassium iodine, hydrocortisone and propylthiouracil. She was kept on propranolol 80 mg q/4h, intravenous esmolol 50 mcg/kg/min, diltiazem drip 5 mg/hr, and was started on Digoxin 0.25 mg q/4h. TSI and TPO were undetectable, and thyroid ultrasound revealed a right nodule measuring 5 x 2.2 x 3.7cm. Thyroid storm was attributed to a toxic nodule exacerbated by exposure to excess iodine (contrast for imaging and amiodarone). Propylthiouracil, hydrocortisone and beta blocker were maximized, and cholestyramine was added, but their heart rate remained elevated, blood pressure worsened requiring synchronized cardioversion. Because of persistent hyperthyroid state, refractory to medical treatment, patient was started on plasmapheresis on day 10 of hospitalization, she underwent 5 sessions with significant reduction in Free T3 and Free T4 (Figure 1), and remarkable improvement in her hemodynamic status and resolution of tachycardia. Patient underwent total thyroidectomy on day 16, without complications. Plasmapheresis has been described as a treatment option for refractory thyroid storm, as a bridge therapy prior thyroidectomy. During plasmapheresis, thyroid-binding globulin, thyroid hormones, cytokines and putative antibodies are removed with the plasma; then the colloid replacement provides new binding sites for circulating free thyroid hormone (2). Although albumin binds thyroid hormone less avidly than TBG, it provides a much larger capacity for low-affinity binding that may contribute to lower free thyroid hormone levels, providing a window for thyroidectomy. 1. Muller C et al, Role of Plasma Exchange in the Thyroid Storm, Therapeutic Apheresis and Dialysis15 (6): 522–531

Time-dependent changes in FT4 and FT3 levels measured using mass spectrometry after an acute ingestion of excess levothyroxine in a case with hypothyroidism

Background: Thyrotoxicosis is common disorder among endocrine dysfunctions. It is not rare that the free thyroid hormone level exceeds the measurement range of immunoassay. Such extreme high concentration of free thyroid hormone is generally considered to be impossible to measure correctly because of changes in the balance between free hormones and binding proteins by dilution of serum. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), however, higher concentrations are able to be determined. Case presentation: We present a case of a 21-year-old female with congenital hypothyroidism who had taken a total of 5 mg levothyroxine over three consecutive days following discontinuance of the medication for a month. Immunoassay performed three hours after the last ingestion showed that the patient’s free thyroxine (FT4) was over 100 pmol/L and her free triiodothyronine (FT3) was 24.5 pmol/L. With a temporary cessation of levothyroxine, the patient was kept for observation without any other medication. Two days after the last ingestion, FT4 was still over 100 pmol/L and FT3 was increased to 28.8 pmol/L. After an additional four days, both FT4 and FT3 levels decreased. Through this period, no thyrotoxic symptom or physical sign had appeared. We also measured FT4 and FT3 levels in her cryopreserved serum by ultrafiltration LC-MS/MS. Her FT4 level measured by ultrafiltration LC-MS/MS on the visiting day and two days later were 160.0 and 135.5 pmol/L, respectively, indicating that the toxic dose of levothyroxine was partly changed to T3 during the two days. The FT3/FT4 ratios were revealed to be low, accounting for the patient’s benign clinical course despite temporal toxic exposure to levothyroxine. It is implied that prior discontinuation of supplementary levothyroxine increases potential vacant binding sites for thyroid hormone as a buffer to prevent toxic T3 effect. Conclusion: It was helpful to clarify the time dependent changes in free thyroid hormone levels by ultrafiltration LC-MS/MS in discussing the clinical course in this case. Though mass spectrometry has a disadvantage in speed for routine laboratory use, its accurate measurement, particularly of levels exceeding the measurable range of the immunoassay, provides valuable information for more appropriate management of extreme thyrotoxicosis.

Time-dependent changes in FT4 and FT3 levels measured using mass spectrometry after an acute ingestion of excess levothyroxine in a case with hypothyroidism

Background Thyrotoxicosis is common disorder among endocrine dysfunctions. It is not rare that the free thyroid hormone level exceeds the measurement range of immunoassay. Such extreme high concentration of free thyroid hormone is generally considered to be impossible to measure correctly because of changes in the balance between free hormones and binding proteins by dilution of serum. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), however, higher concentrations are able to be determined. Case presentation We present a case of a 21-year-old female with congenital hypothyroidism who had taken a total of 5 mg levothyroxine over three consecutive days following discontinuance of the medication for a month. Immunoassay performed three hours after the last ingestion showed that the patient’s free thyroxine (FT4) was over 100 pmol/L and her free triiodothyronine (FT3) was 24.5 pmol/L. With a temporary cessation of levothyroxine, the patient was kept for observation without any other medication. Two days after the last ingestion, FT4 was still over 100 pmol/L and FT3 was increased to 28.8 pmol/L. After an additional four days, both FT4 and FT3 levels decreased. Through this period, no thyrotoxic symptom or physical sign had appeared. We also measured FT4 and FT3 levels in her cryopreserved serum by ultrafiltration LC-MS/MS. Her FT4 level measured by LC-MS/MS on the visiting day and two days later were 160.0 and 135.5 pmol/L, respectively, indicating that the toxic dose of levothyroxine was partly changed to T3 during the two days. The FT3/FT4 ratios were revealed to be low, accounting for the patient’s benign clinical course despite temporal toxic exposure to levothyroxine. It is implied that prior discontinuation of supplementary levothyroxine increased potential thyroid hormone binding capacity as a buffer to prevent toxic T3 effect. Conclusion It was helpful to clarify the time dependent changes in free thyroid hormone levels by LC-MS/MS in discussing the clinical course in this case. Though mass spectrometry has a disadvantage in speed for routine laboratory use, its accurate measurement, particularly of levels exceeding the measurable range of the immunoassay, provides valuable information for more appropriate management of extreme thyrotoxicosis.