A 76 year old woman was admitted to hospital after presenting to the Emergency Department with shortness of breath, productive cough and palpitations. A chest x-ray demonstrated a left lower lobe pneumonia and ECG showed atrial fibrillation with a fast ventricular response. Initial management included intravenous antibiotics, intravenous fluids and oral digoxin loading.
Two days after admission, the patient’s condition had significantly improved and she was able to start mobilising on the ward. The palpitations that she had been experiencing at presentation had also ceased. Following review by the Senior House Officer on the ward round, a repeat ECG was requested when demonstrated that the patient had cardioverted back to sinus rhythm. Digoxin therapy was subsequently held.
To investigate for an underlying cause of atrial fibrillation, thyroid function tests were added to blood tests from admission, with results as listed below.
Haemoglobin 125 g / dL
White cell count 13.7* 109/l
Neutrophils 11.9* 109/l
Platelets 351 * 109/l
Urea 4.6 mmol / L
Creatinine 130 micromol / L
Sodium 139 mmol / L
Potassium 3.6 mmol / L
C-reactive protein 105 mg / L
Thyroid stimulating hormone 0.25 microU / L
T4 free serum 14.1 pmol / L
T3 free serum 7.4 pmol / L
What is the most appropriate next investigation to assess deranged thyroid function tests?
Thyroid ultrasound
Thyroid peroxidase antibody levels
Repeat TFT in 6 weeks
Thyroid scintiscanning
Thyroglobulin antibody levels
Any acute and severe illness may alter thyroid hormone deiodination through the effects of cytokines and result in various changes in levels of TSH, fT3 and fT4. Low TSH levels in hospitalised patients are three times more likely to be due to this effect than to hyperthyroidism.
It is therefore best to avoid thyroid function testing around the time of an acute illness unless there is good clinical evidence of a primary thyroid illness. If TFT remain deranged following recovery from acute illness then further investigation to assess for thyroid disease can be considered.