Subclinical Hypothyroidism Common with Chronic Kidney Disease

By Charles Bankhead
DENVER, 12 june 2008-- Almost 20% of patients with chronic kidney disease have subclinical primary hypothyroidism, according to data from a large cohort of outpatients.
About 10% of unselected patients had subclinical primary hypothyroidism, Michel Chonchol, M.D., of the University of Colorado Health Sciences Center, and colleagues reported online in the Clinical Journal of the American Society of Nephrology.
However, patients with an estimated glomerular filtration rate of less than 60 mL/min/1.73 m2 had a prevalence of 18%.
"Future clinical and experimental studies should explore potential causal mechanisms linking subclinical primary hypothyroidism and chronic kidney disease," the authors concluded.
"The possible adverse effects of subclinical hypothyroidism on cardiovascular risk associated with chronic kidney disease are presently unknown. Whether adult patients with chronic kidney disease should be routinely screened for subclinical hypothyroidism requires further investigation."
An improved capability to detect subtle changes in thyroid function has led to the emergence of the concept of subclinical primary hypothyroidism, defined as elevated serum thyrotropin levels but normal free thyroxine levels.
Subclinical primary hypothyroidism has been associated with markers of cardiovascular risk and impaired cardiac function, the authors said. Moreover, subclinical primary hypothyroidism is an independent predictor of all-cause mortality in dialysis patients and is a risk factor for nephropathy and cardiovascular events in patients with type 2 diabetes.
The prevalence of subclinical primary hypothyroidism in the general population and by different levels of estimated GFR has not been studied extensively. Dr. Chonchol and colleagues performed a cross-sectional analysis of a large database from a clinical chemistry laboratory in Verona, Italy.
The study involved 3,089 adults, 293 (9.5%) of them meeting the laboratory definition for subclinical primary hypothyroidism and 277 (9%) who had an estimated GFR of lower than 60 mL/min/1.73 m2.
The prevalence of subclinical primary hypothyroidism increased from 7% in patients with an estimated GFR ≥90 mL/min/1.73 m2 to 17.9% in patients with an estimated GFR <60 mL/min/1.73 m2 (P<0.0001 for trend).
After adjustment for age, sex, fasting glucose, total cholesterol, and triglycerides, an estimated GFR of lower than 60 mL/min/1.73 m2 increased the likelihood of subclinical hypothyroidism by almost 75% compared with patients who had higher estimated GFR values (OR 1.73, 95% CI 1.20 to 2.48, P=0.003).
"With progressively lower estimated GFR, there was graded increased likelihood of subclinical primary hypothyroidism," the authors said.
The authors noted several limitations of the study. "Because this study is cross-sectional, the present analysis is limited in its ability to establish causal or temporal relationships between subclinical primary hypothyroidism and kidney disease."
"Nonthyroidal (e.g., low T3 syndrome, which is typically seen in some ill patients, including those with end-stage renal disease) and thyroidal causes of subclinical hypothyroidism were not identified."
Dr. Chonchol and colleagues reported no disclosures.

Primary source: Clinical Journal of the American Society of NephrologySource reference:Chonchol M, et al "Prevalence of subclinical hypothyroidism in patients with chronic kidney disease" Clin J Am Soc Nephrol 2008; DOI: 10.2215/cjn.00800208.