Thyroid Research Thyroid Research Archive Hypothyroidism

Patients with hypothyroidism may have high serum concentrations of several enzymes

(November 2002)

The background of the study. Some patients with hypothyroidism have high serum concentrations of creatine kinase (an enzyme found in muscle, including cardiac muscle) and the liver enzymes aspartate aminotransferase and alanine aminotransferase. However, the relationships between the increases and the severity of hypothyroidism, as determined by measurements of serum thyrotropin (TSH), are not clear. These and other enzymes were measured and the results correlated with serum TSH concentrations in a large group of patients with primary hypothyroidism.

How the study was done. The study subjects were 114 patients, aged 7 to 65 years, with spontaneously occurring primary hypothyroidism, with or without thyroid enlargement, as defined by a serum TSH concentration >14 mU/L; serum thyroxine was not measured. Patients with a history of other thyroid diseases or treatment for thyroid disease, with other illnesses, those who had been treated with any drug that affects thyroid function, and pregnant women were excluded. Fasting blood samples were collected before and 3 weeks to 11 months after the initiation of thyroxine therapy for measurements of serum TSH, creatine kinase, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and amylase. No age- and sex-matched normal subjects were studied at the same time.

The results of the study. Forty-seven of the 114 patients (41 percent) had normal serum concentrations of all five enzymes. Among the other patients, 8 (7 percent) had high serum concentrations of creatine kinase, aspartate aminotransferase, alanine aminotransferase, and amylase, and the remainder had high serum concentrations of one to three of these enzymes. Among the individual enzymes, high values were found in from 3 percent to 37 percent of the patients.

Fifty-three patients had serum TSH concentrations <100 mU/L, of whom 38 (72 percent) had normal serum concentrations of all five enzymes. In this group there was no correlation between serum TSH concentrations and the serum concentrations of any of the enzymes. Serum creatine kinase concentrations decreased from high to normal or decreased within the normal range during thyroxine therapy. The patterns of change in the other enzymes were similar.

The conclusions of the study. Among several serum enzymes, the concentrations of creatine kinase are most often high in patients with hypothyroidism, but there is little correlation between serum enzyme and TSH concentrations.

The original article. Saha B, Maity C. Alteration of serum enzymes in primary hypothyroidism. Clin Chem Lab Med 2002;40:609-11.