PMC7236172_01
Results of combined levothyroxine (1000 mug) and paracetamol (1000 mg) oral absorption test in a female patient with suspected levothyroxine malabsorption about 2 years prior to admission to our Department. Darker area represents reference range for free T4 (11.5-22.7 pmol/l)
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Fig1
TSH, however, was above 75 muIU/ml, and she remained profoundly hypothyroid, so a combined LT4 (1000 mug)/paracetamol (1000 mg - type of preparation not specified) absorption test was performed. This showed rather weak absorption of LT4 (about 66% increase in FT4 concentration), but quite good absorption of paracetamol (where the therapeutic target level of paracetamol was assumed to be 10-20 mg/l, i.e. 10-20 mug/ml) (see Fig. 1), at some point she also had 500 mug LT4 absorption test (first sample after 120 min) that showed only 20% increase in FT4.
Results of oral 2500 mug levothyroxine absorption test in a female patient with suspected levothyroxine malabsorption performed in our Department under strict supervision. Darker area represents reference range for free T4 for our assay (0.93-1.70 ng/dl). Avid absorption of levothyroxine is clearly demonstrated followed by near normalization of TSH concentrations after 4 days
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Fig2
Under these circumstances, LT4 absorption test revealed an excellent absorption of LT4, with FT4 concentrations surpassing upper limit of FT4 reference range at 60 min and reaching concentrations about 25 times above the baseline FT4 concentration at 120 min of the test (Fig. 2).