Validity of serum CK activity in the diagnosis of thyroid dysfunction

ABSTRACT

This study assessed the pattern of changes in serum creatine kinase [CK] activity in [100] patients with a variety of clinical manifestations of either increased or decreased thyroid function and evaluated the validity of such changes in the diagnosis of both conditions They were biochemically assessed for thyroid function and compared with a control group of 67 apparently healthy subjects According to thyroid function tests, the subjects were classified into 3 groups Group 1 Hypothyroid patients [n=50], which was divided into 2 subgroups Group A[Overt hypothyroidism] It included 43 patients with TT4 hypothyroidism]. It included 7 patients with TT4> 60 nmol/l. The second group [Group 2] included 50 hyperthyroid patients, while [Group 3] was composed of 67 euthyroid subjects. Serum CK activity was noticeably elevated in hypothyroid patients compared to both normal and hyperthyroid subjects [mean +SD was 204.10 + 97.72 Vs 79.97+ 26.35 and 79.36 + 26.88 u/L respectively]. There was no significant difference in the mean serum CK activity between group A and B [Z =87, P>0.05] A significant positive correlation was revealed between serum TSH and CK in hypothyroid patients [Group I] where [r=0.35, P<0.01], while there was no such significant association in either group A or B [p>O.O5],and thus did the hyperthyroid patients [r= -0.22, P>0.05]. For patients in group1, the sensitivity, specificity, positive predictive value [PPV], negative predictive value [NPV], accuracy rate, positive likelihood ratio [PLR] and negative likelihood ratio [NLR] of elevated serum CK activity as a diagnostic test were 74%, 95.5%, 92.5%, 87%, 86%, 16.40, 0.27 respectively. However, they were 0%, 95.5%, 0%, 56%, 5.4%, 0 and 0.96 respectively for the diagnosis of hyperthyroidism. In conclusion high serum CK activity is a fairly sensitive and highly specific test for the diagnosis of hypothyroidism with a high PPV value mainly for overt [uncompensated] cases. This study indicates that the determination of CK might be a useful screening tool for hypothyroidism