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.
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