Chronic Kidney Disease and the Thyroid – Renal and Urology News

It is well known that chronic kidney disease (CKD) has an impact on many body systems. Perhaps underappreciated is the link between the kidney and the thyroid. Increasing understanding of the relationship between the kidney and thyroid offers a largely unexplored opportunity to improve management of patients with CKD, in whom thyroid problems are frequently under-recognized.

An estimated 20 million Americans have some type of thyroid disease. Disconcertingly, it is also estimated that 60% of those with a thyroid condition are unaware of it.¹ With regard to CKD, subclinical hypothyroidism has been found to increase from 7% to 17% in people whose glomerular filtration rate (GFR) drops to 60 mL/min/1.73 m² from 90 mL/min/1.73 m² or higher.² Recent research indicates that subclinical hypothyroidism can be considered an independent predictor of CKD in the general population, even when adjusting for other common risk factors such as age, hypertension, and obestiy.³

What is this relationship between the kidney and the thyroid? The effects of poor thyroid function on the kidney are widespread, including reduced renin-angiotensin-aldosterone system (RAAS) activity, reduced GFR, and decreased heart rate and cardiac output that leads to diminished renal blood flow and ischemic kidney injury.⁴ CKD is thought to negatively impact thyroid function through multiple pathways. One such pathway is reduced expression of 1 5’-deiodinase that leads to decreased conversion of T4 to T3. Indeed, the most common finding is not an elevated TSH, but low T3.² However, TSH is the most common and typically only laboratory measure used to assess thyroid function, which can result in underdiagnosis of thyroid disease. This is significant because it is estimated that GFR is reversibly reduced by about 40% in more than half of adults with hypothyroidism.⁴

Providers can improve CKD care by:

• Regularly screening for thyroid issues by ordering a full thyroid panel. Because TSH is not a reliable marker of thyroid issues in patients with CKD, a full thyroid panel including TSH, free T3, Free T4 and TPO antibodies would be more informative. It is important to recheck thyroid function as GFR changes as well.²
• Considering patient symptoms. Subclinical hypothyroidism is common in those with CKD, which may mean laboratory values look normal but patients present with common hypothyroidism symptoms like cold intolerance, fatigue, brain fog, hair loss, joint and muscle pain, increased cholesterol and triglycerides, unintentional weight gain or difficulty sleeping.⁵ These symptoms can be common in CKD due to anemia or other common coexisting conditions, so testing is important to properly identify the root cause.
• Ensuring adequate micronutrients and amino acids. T4 to T3 conversion and thyroid function require several micronutrients, such as zinc, iodine, selenium, choline, iron, folate, and essential amino acids. This is an important consideration if the patient is on a T4-only thyroid medication or on a low-protein or plant-based diet.⁶ A dietitian can play an important role in assessing nutrient need, guiding diet changes and recommending appropriate supplements.
• Managing stress. Cortisol can inhibit conversion of T4 to T3 and actually increase conversion of T4 to reverse T3.⁷ While stress management support is not a typical responsibility of nephrology providers, providing tools or referrals to support patients is appropriate. Measures that can reduce stress include meditation, counseling, and vagus nerve stimulation.⁸ 

Thyroid disease is under-recognized in many individuals. Because thyroid disease can affect kidney health (and vice versa), nephrology providers are uniquely poised to investigate and identify thyroid issues. As with many connected issues in CKD, nephrology providers need not shoulder the responsibility of treating thyroid disease, but refer out to dietitians, endocrinologists, and other appropriate providers to ensure the patient is getting the best care possible. It is not fully understood how much of an impact supporting thyroid health can have for those with CKD, but with a few simple proactive steps providers can begin to see possibilities.

Lindsey Zirker MS, RD, is a renal dietitian and Director of Clinical Services for the Kidney Nutrition Institute in Titusville, Florida. She specializes in autoimmune kidney disease and advanced practice medical nutrition therapy for people with kidney disease.