The Etiology of Abnormal TSH in Veterans Cared by a VA Medical Center - One High Serum Thyrotropin is Associated with Higher 5-Years Mortality.

Objective: By analyzing the etiology of abnormal TSH in randomly selected veteran patients, we set our heart on improving future clinical care/management of the clinical/subclinical hyper- and hypothyroidism in the aging veteran population.

Methods: A total of 1100 patients' charts in alphabetical order were selected. Excluded cases of insufficient information, 897 patients' charts were reviewed and analyzed for causes of abnormal TSH. Among them, 602 for the cause of low TSH (below 0.55 uU/mL) and 295 for high TSH (above 4.78 uU/mL) were reviewed retrospectively.

Findings: Among the 1100 patients selected, 680 (61.8%) were 60 y or older (female=44, 6.8%); 420 were under 60 y (female=80, 19.0%); significantly more female patients were found in the younger age group (P<0.001). After excluding patients with insufficient data, the most common cause of suppressed TSH is iodine-induced, CT iodinated contrast and betadine use caused 35.0% in the older group (n=126) compared to 23.6% in the younger group(n=57) (P = 0.027). The significant difference is that older veterans received more contrast CTs (P < 0.05 compared to the younger group). In both age groups with concurrent FT4 study, we found four high FT4 among 90 studies, 4.4% overt hyperthyroidism. The second most common cause of suppressed TSH is due to thyroid hormone (TH) replacement in the older group (119 patients, 33.1%) with age > 60y, significantly more frequent compared to the younger group, P<0.001. There is significantly more overt hyperthyroidism, 27.8/%, than the iodine-load induced suppression of TSH, P<0.001, due to 17 patients on TSH suppression therapy after total thyroidectomy for thyroid cancer. Among the 295 patients with elevated TSH, the most common cause of high TSH was due to hypothyroidism on T4 replacement: a total of 128 (59.3%) in the older group (N=216) is, similar to 47 (59.5%) in the younger group (N=79). In both age groups, there were 139 patients with concomitant FT4 measurement; 17 overt hypothyroidism were found, 12.2%. No significant difference is seen in the two age groups. The next most common causes of elevated TSH are CT contrast infusion, 23 (10.6%) in the older group and 7 (8.9%) in the younger group. We find high TSH is associated with a higher death rate of 101/238 (42.4%) in a 5-year follow-up (from 2016 to 2021), as compared to low TSH of 68/238 (28.6%), in the older age group, p<0.03； both were significantly higher than the age- and sex-matched general US population, 19.7%, P<0.01.

Conclusion: Even though most, ~ 90%, were subclinical, the suppressed and elevated TSH are associated with severe consequences in CV/CNS and immune-suppression complications in aging veterans. Therefore, cautious use (and more frequent check of TSH) of TH replacement and CT contrast in aging veterans is recommended. The alarming increase in 5 years death rate in older patients with elevated TSH deserves further study.