Endocrine Journal 2001, 48 (6), 717-722 NOTE Cross-Reactive Mechanism for the False Elevation of Free Triiodothyronine in the Patients Treated with Diclofenac KEIZO KASONO, HAJIME HIKINO*, SHINJI FUJINO**, NoBUYUKI TAKEMOTO*, TosHIHIRO KAI*, KIYosHI YAMAGUCHI***, FUMio KONISHI* AND MASANOBU KAWAKAMI Department of Endocrinology and Metabolism, Jichi Medical School, Omiya Medical Center, 1-847, Amanuma-cho, Saitama 330-8503, Japan *Department of Surgery , Jichi Medical School, Omiya Medical Center, 1-847, Amanuma-cho, Saitama 330-8503, Japan **Department of Pathology , Jichi Medical School, Omiya Medical Center, 1-847, Amanuma-cho, Saitama 330-8503, Japan ***Department of Neurology , Jichi Medical School, Omiya Medical Center, 1-847, Amanuma-cho, Saitama 330-8503, Japan Abstract. We report three cases of patients exhibiting a false elevation of serum free triiodothyronine (FT3) as a result of a cross-reaction with diclofenac. The first case is a 66-yr-old woman with a long history of rheumatoid arthritis (RA). The patient was receiving diclofenac for the treatment of her RA. The patient was subsequently diagnosed as having thyroid papillary adenocarcinoma and received a subtotal thyroidectomy. After the operation, the patient exhibited postoperative hypothyroidism except for a gradual elevation of FT3. The other two patients also exhibited an elevated serum FT3 level after the administration of diclofenac. Serum FT3 levels in these pa- tients decreased to normal or below normal after diclofenac administration was discontinued. In the first case, the elimination of immunoglobulin from the sera using polyethylene glycol precipitation did not reduce the FT3 level. In our hospital, Vitros ECi (enhanced chemiluminescence enzyme immunoassay) system and Vitros FT3 kit were used for FT3 assay. The patient's FT3 levels were normal or below normal when they were measured using other FT3 kits. FT3 was also detected when diclofenac was dissolved in a phosphate buffered saline. Therefore, we concluded that a cross-reaction between FT3 and diclofenac was the mechanism causing the false elevation of FT3 in these pa- tients. Key Words: Triiodothyronine, Thyroid, False elevation, Cross-reaction, Diclofenac (Endocrine Journal 48: 717-722, 2001) CLINICAL tests for evaluating thyroid function in- tion tests [2-6]. Diclofenac is a commonly used clude the measurement of TSH, FT4, FT3, T4 and NSAID that binds to thyroid hormone binding pro- T3. Circulating thyroid hormones are tightly bound teins, leading to the release of FT3 or FT4. There- to several serum proteins, including thyroxine bind- fore, the drug slightly raises free thyroid hormone ing globulin (TBG), thyroxine binding prealbumin levels and reduces total T4 and T3 concentrations [7, (TBPA), and albumin [1]. Nonsteroidal anti- 8]. Autoantibodies against hormones being assayed, inflammatory drugs (NSAIDs) as well as various heterophilic antibodies to immunoglobulins used in other medications, are known to affect thyroid func- the assay kits and rheumatoid factors (RF) may also interfere with the accurate measurement of hormone levels [9-12]. Cross-reactions with administered Received: May 11, 2001 drugs [13] or serum proteins [14J are a common cause Accepted: August 15, 2001 of falsely elevated hormone concentrations. In this Correspondence to: Dr. Keizo KASONO, Department of report, we describe the false elevation of serum FT3 Endocrinology and Metabolism, Jichi Medical School, Omiya Medical Center, 1-847, Amanuma-cho, Saitama 330-8503, levels assayed by Vitros FT3 kit in three patients. Japan We concluded that a cross-reaction with diclofenac 718 KASONO et al. was the mechanism for the false elevation of FT3. In thyroglobulin antibodies and anti-microsomal anti- the first case, the false elevation of FT3 concentra- bodies were negative, TSH receptor antibody was tions in the patient's sera was affected by the pa- 1.2% (normal 0-15%), thyroglobulin was 6.6 pg/L tient's thyroid function. In severe hypothyroid (normal 0-30 ag/L), RF was 944 IU/ml, T-Chol was state, the elevation of FT3 was even more remarka- 4.09 mmol/L and ALP was 161 U/L. On the basis ble. An inverse relationship between FT3 level and of this data, we eliminated the diagnosis of autoim- thyroid function was thus observed in the first pa- mune thyroiditis and diagnosed her as postoperative tient. hypothyroidism with falsely evaluated FT3 concen- tration. Since the patient complained of slight general fatigue, we started to prescribe T4 (50 Case Report pg/day) for hypothyroidism, beginning on April 21, 1999. After starting medication, thyroid function Case 1 gradually returned to normal and the general fatigue A 66-year-old woman with a 30-year history of RA disappeared. On January 17, 2000, serum FT4 was was diagnosed as having thyroid papillary adenocar- 22.7 pmol/L, FT3 was 9.39 pmol/L and TSH was cinoma. A subtotal thyroidectomy was performed 4.02 mU/L. on January 27, 1999. Before operation, serum FT4 was 17.6 pmol/L (normal, 10.4-20.3 pmol/L), FT3 Interpretation of the mechanism for the false ele- was 8.45 pmol/L (normal, 4.27-8.12 pmol/L), and vation of FT3 in case 1 TSH was 1.48 mU/L (normal, 0.47-4.71 mU/L). RF was 608 IU/ml (normal, 0-15 IU/ml), total cho- To elucidate the mechanism of the false elevation lesterol (T-chol) was 3.44 mmol/L (normal, 3.29- in serum FT3, we performed several examinations. 5.96 mmol/L) and alkaline phosphatase (ALP) was The patient agreed orally to an additional blood 162 U/L (normal, 89-285 U/L). Although the FT3 sampling for the purpose of this study. level was slightly higher than normal, the TSH was In our hospital, thyroid function including FT3, not suppressed, and she had no signs of thyrotoxi- FT4, T3, T4 and TSH was routinely assayed using cosis. She had previously undergone an operation Vitros Eci (enhanced chemiluminescence enzyme im- for a carcinoma in her left breast in 1997. At the munoassay) system. These kits were purchased from time of thyroidectomy, she was taking the following Ortho-Clinical Diagnostics Inc. (Cardiff, UK). The medications: long-acting diclofenac (75 mg/day), principle of FT3 measurement in Vitros FT3 kit is tamoxifen (20 mg/day), retinol palmitate (30,000 competitive immune reaction using peroxidase- U/day), methotrexate (7.5 mg/week), active form of labelled sheep anti-FT3 polyclonal antibodies. When vitamin D (0.75 pg/day), Vitamin C (600 mg/day), the patient's stocked sera was assayed using the and tocopherol nicotinate (300 mg/day). After sub- Amerlex FT3 RIA kit from the same company or total thyroidectomy, serum FT4 concentration grad- using kits purchased from other companies, the FT3 ually decreased and TSH level increased remarkably concentrations were lower than normal (data not (Table 1). On April 20, 1999, FT4 was 9.27 pmol/L, shown). These results confirmed the diagnosis of FT3 was 12.1 pmol/L, TSH was 75.9 mU/L, anti- postoperative hypothyroidism in the patient. Table 1. Thyroid function of case 1 FALSE ELEVATION OF FREE TRIIODOTHYRONINE 719 Polyethylene glycol (PEG) precipitation was em- new Vitros FT3 kit may solve the disturbance with ployed to remove the immunoglobulin fraction from diclofenac in the assay. The T3 and FT4 concentra- the patient's serum. We used stocked samples col- tions assayed by the Vitros kits were also slightly lected on three different days: January 22, March 19 elevated after the administration of diclofenac. As and April 20, 1999. The FT3 concentrations were previously reported, serum TSH was weakly sup- reassayed using the Vitros FT3 kit before the PEG pressed after diclofenac administration [8, 16]. precipitation and values of 5.84, 6.67 and 7.68 These results suggested that a cross-reaction be- pmol/L were obtained, respectively. A slight reduc- tween FT3 and diclofenac or its metabolites might tion in FT3 levels occurred in the samples that had have caused a false elevation of FT3 level. To been stocked for a long period of time. After the confirm this mechanism, cyclooxigenase-2 (Cox-2), a PEG precipitation, the FT3 values for these three target enzyme of diclofenac, was used to neutralize samples were 5.59, 6.93 and 8.45 pmol/L, respec- the drug. First, two normal volunteers were ad- tively. The levels before and after PEG precipitation ministered by diclofenac (75 mg/day) for 3 days. showed no significant difference. This showed that One-hundred microliters of their sera were added to RF and other immunoglobulins were not involved in frozen tubes containing 10 it of a Cox-2 reaction the mechanism that produced the false elevation of solution containing 300 iM of diethyldithiocarba- FT3 level. mate (Wako, Osaka, Japan), 1.0% trehalose (Wako) To evaluate the effect of diclofenac on thyroid and 1 U of Cox-2 (Alexis Biochemicals, San Diego, function in the patient, the drug was removed from CA). The mixture of serum and Cox-2 was im- the patient's prescription. Diclofenac was replaced mediately used for FT3 assay using the Vitros FT3 with loxioprofen for seven days. The patient was kit. Before Cox-2 treatment, their FT3 concentra- then given one capsule of long-acting diclofenac (37.5 tions assayed by Vitros FT3 kit were 16.2 and 11.4 mg/C) in the morning, and serum samples were taken pmol/L, respectively. After the addition of Cox-2 to before and 1 to 8 hours after the administration. their sera, the FT3 values decreased to 6.98 and 6.34 Table 2 shows the high concentration of FT3 that was pmol/L, respectively. detected by the Vitros FT3 kit after the admin- Finally, we measured the FT3 level in a diclofenac istration of the long-acting diclofenac.