Resumen de Levothyroxine Absorption Test in the management of a patient with persistent hypothyroidism

Joana André Monteiro, Marta Ferreira, Miguel Pires, Célio Fernandes

• Hypothyroidism refers to the common pathological condition of thyroid hormone deficiency. If untreated, it can lead to serious adverse health effects and ultimately death1 . Synthetic thyroxine has been used to treat hypothyroidism successfully since 19272 . The optimal daily dose of 1.6- 1.8 ug/body weight (kg) per day of levothyroxine (LT4) is an appropriate replacement dose1–3. The absorption of oral LT4 occurs mostly in the jejunum and ileum (60–80% of the ingested dose)3–6. It is maximal when the stomach is empty and takes place within the first 3 hours of ingestion2 .

  For patients who require larger doses of LT4 than expected, the underlying cause can be challenging to determine2 . Several factors must be considered: low patient compliance, reduced LT4 absorption from interfering dietary factors and medications, or gastrointestinal disorders contributing to malabsorption7 .

  The most common cause of mal-absorption is poor or non-compliance with oral LT4 treatment by the patient8 . Compliance with treatment is the key to good outcomes in medical care.Medical non-compliance is a major public health problem that imposes a considerable financial burden upon modern healthcare systems and is also a source of ongoing frustration to doctors9 .

  The concept of pseudo-malabsorption of thyroid hormones was first outlined in 1991 when it was described a factitious disorder due to patient non-compliance with the intention to deceive10. An effective way to distinguish nonadherence from mal-absorption is to perform levothyroxine absorption testing (LAT)5 .

  This article aims describe the LT4 absorption rapid test in a patient with hypothyroidism, highlighting its importance in the diagnosis of LT4 pseudo-malabsorption.