Here are some examples of hypothyroid patients who have ‘normal’ TFTs consistent with a Subnormal TSH. Note this is usually not considered secondary hypothyroidism as other pituitary hormones are normal and TSH, fT3 and fT4 may be within their reference intervals. My thanks to the patients who kindly consented to publication.
Patient 1
- TSH 1.25 mIU/L (0.27 – 4.20)
- Free T4 11.44 pmol/L (12.00 – 22.00)
- Free T3 3.85 pmol/L (3.10 – 6.80)
- TBG 19.045 IU/mL (0 – 115)
- TPO 21.21 IU/mL (0 – 34)
‘All the hypothyroid symptoms, sleeping my life away’
Patient 2
- TSH 2.43 mIU/L (0.27 – 4.20)
- Free T4 13.40 pmol/L (12.00 – 22.00)
- Free T3 4.00 pmol/L (3.50 – 7.70)
- TBG 103 IU/mL (0 – 115)
- TPO 14.50 IU/mL (0 – 33)
This patient is cold, has dry skin, very tired, depressed and has cognitive problems. Their doctor and several endocrinologists refuse to make a diagnosis – because ‘TFTs are normal’.
Patient 3
- TSH 1.124 mIU/L (0.27 – 4.20)
- Free T4 11.17 pmol/L (12.00 – 22.00)
- Free T3 3.93 pmol/L (3.10 – 6.80)
This patient has had multiple symptoms for 30 years: extreme fatigue, muscle and joint pain, dry skin, brittle nails, hair loss and elevated cholesterol. They were given diagnoses of ME and fibromyalgia. They were unable to tolerate a trial of 25 mcg levothyroxine plus a small dose of liothyronine. (Later, we will see how levothyroxine can make this group of patients more hypothyroid).
Patient 4
- TSH 0.53 mIU/L (0.32 – 4.00)
- Free T4 11.1 pmol/L (9.00 – 19.00)
- Free T3 3.2 pmol/L (3.10 – 6.20)
- TSH 0.24 mIU/L (0.32 – 4.00)
- Free T4 11.0 pmol/L (9.00 – 19.00)
- Free T3 3.7 pmol/L (3.10 – 6.20)
- TBG <10 (0 – 40)
- TPO 11 (0 – 30)
This patient is exhausted and feels terrible. They are given diagnoses of Fibromyalgia, IBS and CFS/ME. GPs and endocrinologist refuse to diagnose because TFTs are ‘normal’. ‘I have every symptom of hypothyroidism, but nobody will help me‘.
Patient 5
- TSH 2.13 mIU/L (0.27 – 4.20)
- Free T4 13.6 pmol/L (12.00 – 22.00)
- Free T3 3.7 pmol/L (3.10 – 6.80)
- TBG < 10 IU/mL (0 – 115)
- TPO 1.4 (0 – 34)
This patient has multiple symptoms: fatigue, aches and pain, depression, cold, impaired memory. The blood tests were considered normal, so they were given a diagnosis of CFS.
An Example From the Literature
Myxedema Coma in a Patient with Subclinical Hypothyroidism
Myxedema Coma in a Patient with Subclinical Hypothyroidism.
Akhila Mallipedhi, Hamza Vali, and Onyebuchi Okosieme. Thyroid. 2011;21(1):87-9.
DOI: 10.1089/thy.2010.0175
This extraordinary case illustrates how subnormal TSH can lead to severe hypothyroidism.
- TSH 14.00 mIU/L (0.4 – 4.0)
- Free T4 14.3 pmol/L (10.3 – 24.5)
- Free T3 4.45 pmol/L (2.67 – 7.03)
The patient was admitted complaining of fatigue. These results indicate mild thyroid failure but not a subnormal TSH. She was prescribed 50 mcg levothyroxine daily.
—————————————————————————————————————————–
- TSH 6.09 mIU/L (0.4 – 4.0)
- Free T4 10.7 pmol/L (10.3 – 24.5)
- Free T3 2.7 pmol/L (2.67 – 7.03)
The patient forgot to take her medication and was admitted to hospital a month later feeling dreadful with pains in the arms and calves. She deteriorated and was diagnosed with myxoedema coma which was successfully treated with liothyronine. Her TSH response was subnormal (lower than might be expected for her combined fT3, fT4).
—————————————————————————————————————————–
- TSH 3.21 mIU/L (0.4 – 4.0)
- Free T4 13.2 pmol/L (10.3 – 24.5)
- Free T3 4.5 pmol/L (2.67 – 7.03)
At week 20 the patient suffered severe lethargy with cramps demonstrating again that low normal fT3, fT4 with a non-elevated TSH can present with severe signs and symptoms.
Let’s try and understand What Happens in Subnormal TSH.