differentials for raised tsh and raised t4

For elevated thyroid-stimulating hormone (TSH) levels in conjunction with elevated thyroxine (T4) levels, key differential diagnoses include resistance to thyroid hormone and TSH assay interference NICE CKS. These possibilities are typically considered when a person has a persistently raised TSH despite adequate or escalating levothyroxine (LT4) treatment doses, and other underlying causes have been excluded or managed NICE CKS. An endocrinologist may arrange additional blood testing to exclude TSH assay interference or resistance to thyroid hormone NICE CKS. Other factors that can lead to persistently abnormal thyroid function tests despite LT4 treatment, potentially contributing to a complex picture, include non-compliance with prescribed LT4 treatment, drug interactions that may reduce LT4 absorption or increase LT4 requirements, and gastrointestinal conditions causing malabsorption NICE CKS.