Serum cholesterol, PBI and ankle jerk time (AJT) were measured simultaneously in a group of not yet treated patients, where a relatively steady state of thyroid function was expected, and in a treated group, where change to lower thyroid function was supposed (thyrostatic drugs, near total thyroidectomy, radioablation of thyroid). 2. Serum cholesterol correlated poorly with PBI (r = --0,4427), better correlation was achieved after logarithmic transformation of PBI values (r = --0,6839). 3. Reference line and covariance between log PBI and serum cholesterol in decreasing thyroid function did not differ significantly from reference line and covariance in steady state, showing that serum cholesterol accompanies closely and without greater delay the changing PBI. Great dispersion of individual values shows a relatively low diagnostic value of serum cholesterol for assessment of functional thyroid state in individual patients. Early reactivity of serum cholesterol level and highly significant correlation with log PBI makes this parameter useful for longitudinal evaluation of therapy in individual patients. 4. Reference line between AJT and serum cholesterol in decreasing thyroid function was shifted to lower AJT values, showing a delay of response of AJT. Tested by analysis of covariance this delay was marked in young patients (0,5% level of significance), present in medium age (5% level of significance), not detectable in person over 60 years. 5. Delay of AJT changes in decreasing thyroid function is important for clinical practice. Our findings are further in accordance with the assumption, that subcellular systems in skeletal muscle may be responsible for delayed response of AJT, being more important than concomitant changes in serum T3/T4 ratio.
