The spectrum of Thyroid function Abnormalities and associated Biochemical factors in Patients with Chronic Kidney Disease in Cameroon

Background: Chronic Kidney Disease (CKD) can lead to thyroid function disorders. The extent to which this relationship exists among Cameroonian CKD patients is not known. The aim of this study, was to determine the spectrum of thyroid dysfunction (TD) and their associated factors among CKD patients in Cameroon. Methods: A cross-sectional study was conducted over a period of 12 months (July 2018 to August 2019) in three referral hospitals (Douala General Hospital, Laquintinie Hospital, Bafoussam Regional Hospital) in Cameroon with patients aged 18years and above diagnosed of CKD stage 1 to 5. Patients with stage 5 dialysis and those on thyroid altering medication were excluded. For each participant, we collected socio-demographic and clinical data. Sera were used to determine thyroid hormone profile, lipid profile, liver test, urea, creatinine, calcium, phosphate and uric acid levels. Albumin creatinine ratio (ACR) was estimated. The diagnosis of CKD was done by a nephrologist and classifies using estimated Glomerular Filtration Rate (eGFR) or urinary albumin creatinine ratio at the time of the study. Results: A total of 374 participants were enrolled with male forming the majority (233(63.66%)). The mean age was 55.85(±13.72) years with an overall prevalence of TD was 57%. Hypertension, diabetes, and gout were the most common comorbidities. In total, 14 types of TDs were identified and grouped into major and minor types. The major types were subclinical hypothyroidism, primary subclinical hypothyroidism, primary overt hypothyroidism, subclinical hyperthyroidism, and overt hyperthyroidism. Low T3 syndrome, low FT3, combine low T3 and low FT3 were the most common minor types. TD increases with the stages of CKD. After logistic regression, albumin [OR: 0.961(0.93-0.991); p=0.015], phosphate [OR: 1.028 (1.014 1.045); p=0.001] and calcium [OR: 0.963 (0.941-0.983); p ˂0.001)] were independently associated to TD. Conclusion: The Spectrum of TD is vast. Low T3, Low FT3, hypothyroidism, combine Low T3 and Low FT3 are the most common thyroid dysfunction. Altered calcium, Phosphate and albumin, were associated to TD in CKD.


Introduction
Chronic kidney disease affects almost every organ-system in the body, and its common complications include; abnormal levels of metabolic waste such as urea and creatinine, mineral bone disorders like hypocalcemia, and hyperphosphatemia, dyslipidemia and thyroid dysfunction [1].
The kidney plays an important role in the metabolism, degradation, and excretion of thyroid hormones [2][3][4]. Therefore, long-standing and progressive deterioration of renal structure and function such as in chronic kidney disease (CKD) can alters the synthesis, secretion, metabolism, and degradation of thyroid hormones which then presents with different clinical syndromes of thyroid dysfunction [5][6][7][8]. Multiple mechanisms can account for these syndromes: lowering circulating thyroid hormone concentration, alteration of peripheral hormone metabolism, disturbed binding to carrier proteins, possible reduction in tissue thyroid content and increased iodine stores in thyroid glands [9]. Triiodothyronine (T 3 ), the most metabolically active thyroid hormone, for instance, can be reduced in CKD patients even with a normal TSH level. This is termed as 'Low T 3 Syndrome' [9,10]. Thyroid dysfunction may present in one of the following patterns: thyroid enlargement (diffuse or nodular); thyroid hormone deficiency or excess (hypothyroidism or hyperthyroidism); asymptomatic or symptomatic (the subclinical state or overt) [11].
Epidemiological studies have shown that the prevalence of thyroid function abnormalities especially hypothyroidism, is substantially higher in persons with chronic kidney disease compared to the general population [10]. In Nepal, South Korea, thyroid dysfunction was found in 38.6 % of patients, with subclinical hypothyroidism (27.2 %), overt hypothyroidism (8.1 %) and subclinical hyperthyroidism (3.3 %) being the most common types encountered [2,3]. In North India (Chennai), 66 % of CKD patients were reported to have thyroid dysfunction. Low T 3 syndrome accounted for 58% against 8 % for hypothyroidism [13]. In Nairobi, Kenya, 42% of patients were found to have thyroid dysfunction. 14% had non-thyroidal illness, subclinical and primary hypothyroidism accounting for 15% while different forms of hyperthyroidism accounted for 13 % [7]. Many cases of hypothyroidism may remain latent or undiagnosed in advanced CKD due to symptoms overlapping with uremia and co-existing Comorbidities. The kidney is not only an organ for metabolism and elimination of TH, but also a target organ of some of the iodothyronines' actions. Thyroid dysfunction causes remarkable changes in glomerulo tubular functions, electrolyte and water homeostasis. Hypothyroidism is accompanied by a decrease in glomerular filtration, hyponatremia, and an alteration of the ability for water excretion. Excessive levels of TH generate an increase in glomerular filtration rate and renal plasma flow. Renal disease, in turn, leads to significant changes in thyroid function. The association of different types of glomerulopathies with both hyper-and hypofunction of the thyroid has been reported. Less frequently, tubulointerstitial disease has been associated with functional thyroid disorders. Nephrotic syndrome is accompanied by changes in the concentrations of TH due primarily to loss of protein in the urine. Acute kidney injury and chronic kidney disease are accompanied by notable effects on the hypothalamus-pituitarythyroid axis. The secretion of pituitary thyrotropin (TSH [6]. These patients with thyroid dysfunction may have clinically important reductions in estimated glomerular filtration rate (eGFR), which can be attenuated by using thyroid hormone replacement therapy [14]. When hypothyroidism becomes severe it can cause reduced cardiac function and lead to progressively worsening of kidney function. Thus thyroid dysfunction may worsen the morbidity in CKD patients and increase cardiovascular mortality [15].
Hypothyroidism can also lead to hyperlipidemia and atherosclerosis in coronary and peripheral vessels. Previous studies have indicated that subclinical and clinical hypothyroidism were the risk factors for all-cause mortality and CVD (Cardiovascular Disease) death. Low T 3 syndrome is an independent predictor of cardiovascular mortality in CKD patient [9,10].
Biochemical factors in CKD that affect thyroid function as well as the spectrum of thyroid function abnormalities are not well known, as such we sort to determine the spectrum of thyroid dysfunction and its associated biochemical profile in CKD patients.

Materials and Methods
We carried out a cross-sectional study at the Littoral region (Laquintinie and Douala General Hospitals) and West Region (Bafoussam Regional Hospital) of Cameroon. These health facilities were selected because they provide care to a vast majority of the population in their respective regions and they host a wide range of socio-economic classes. Each of these hospitals is equipped with a nephrology unit that is under the responsibility of at least 1 nephrologist.

Ethical Consideration
The protocol of this study was submitted to and approved by

Inclusion criterion
The target population was made of adult (≥ 18 years) patients diagnosed with CKD by the nephrologists of the study centers.

Exclusion criteria
Patients with known thyroid disorders, those on medications affecting thyroid function (e.g Amiodarone, propranolol), those

Am J Biomed Sci & Res
Copy@ Jules Clement Assob Nguedia on maintenance hemodialysis or with nephrotic range proteinuria were not included in the study.

Study procedure
After a detailed explanation of the study and obtaining written consent or assent, a questionnaire was used to collect sociodemographic features (age and sex) and clinical data from each participant and using their medical records. A blood sample (5 ml) was collected from each the subjects who agreed to participate in the study as well as those who met the inclusion criteria using a vacutainer plain tubes and was left for a short time to allow the blood to clot and then serum samples were obtained by centrifugation at 3000 rotation per minutes for 10 minutes. The serum obtained after centrifugation was used to determine thyroid

Determination of CKD Parameters
Chronic Kidney Disease: eGFR< 60 ml/min per 1.73 m 2 for more than 3 months with or without evidence of kidney damage or albuminuria (≥ 30 mg/g) with or without decreased GFR for ≥ 3 months, as diagnosed by a nephrologist [17][18][19].
Estimated glomerular filtration rate (eGFR) was computed from serum creatinine using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation [20].
Chronic kidney disease stages were defined as described by the Albuminuria was used to describe albumin creatinine ratio(ACR) between 30 and 299 mg/g and 300 mg/g or over, respectively [22,23].

Nephrotic range Proteinuria was defined as proteinuria of 3+
to 4 or as albuminuria of > 2.2g/g [24].

Definition and classification of categories of thyroid dysfunction
Thyroid dysfunction was considered if patients' thyroid hormones fall outside the reference range. The categories of thyroid dysfunction were classified based on the reference intervals for the hormones and pattern of derangement in the thyroid hormones profile.
The abnormal thyroid function tests result was classified into any of the following:  (Table I).

Prevalence by stages of CKD
The prevalence of thyroid dysfunction was 57, 38% and was found to increase with the severity of CKD, with stage 5 having the highest prevalence of 25.1 % (Figure 1).

Am J Biomed Sci & Res
Copy@ Jules Clement Assob Nguedia

Comorbidities associated with thyroid dysfunction
Age above 50years was the only factor significantly related with thyroid dysfunction(p<0.05) ( Table 2).

Association between biomarkers of CKD and thyroid dysfunction
Serum urea, creatinine, albumin, ACR, calcium and phosphate were significantly associated with all forms of thyroid dysfunction (p<0.05) ( Table 3).

Association of Thyroid Function Abnormalities with Liver Biomarkers
Only ALT was significantly associated with all forms of thyroid dysfunction (p<0.05) ( Table 4).

Association of Thyroid Function Abnormalities with Lipid Profile
Only HDL was significantly associated with all forms of thyroid dysfunction (p<0.05) ( Table 5).  (Table 6).

Discussion
In this study, of which our objectives were to determine the prevalence, describe the spectrum and biochemical factors associated with thyroid function abnormalities in patients with CKD, we found a high prevalence of thyroid dysfunction and an impressive array of abnormalities. We, however, proceeded to classify them as either major or minor based on data reported in recent literature; the most frequently identified and cited as well as those of proven direct clinical significance were classed as major and vice.
The prevalence of thyroid function abnormalities was 57.4%.
This is similar to that in India, estimated at 58% [25]. It is, however, higher than that in Nepal (38.6 %) and Nairobi (42%) [3,7]. Given that thyroid function deteriorates as CKD worsens, it was most likely to find patients with thyroid dysfunction. The high prevalence of thyroid dysfunction can be explained by several factors; a. Metabolism of thyroid hormones occurs mostly in the kidney, as a consequence deterioration in kidney function leads to altered thyroid physiology [27]. Our population consist principally of persons with altered kidney function as such a high prevalence of thyroid dysfunction.
b. Age; most participants were elderly with a mean age of 55years and the 61-70years age group being the most frequent. The D1-785T variant of the D1 receptor involved in the conversion of T 4 to T 3 can undergo polymorphism and results in a decreased activity of D1 [28]. Although the D1-785T variant is not associated with serum rT 3 levels in the general population, its association with lower levels of T 3 in an elderly population can supports the hypothesis of lower activity of D1 in carriers of this polymorphism [28]. In young subjects, a decreased T 3 production by D1 may be masked by the production of serum T 3 by skeletal muscle D2. Throughout adult life, skeletal muscle size and strength gradually decline, resulting in a decrease in D2-expressing skeletal muscle.
Furthermore, rT 3 levels increase with age, and degradation of the D2 protein is accelerated when it is exposed to its substrates T 4 and rT 3 [28,29]. This results in the increased possibility of developing thyroid dysfunction in advanced age (Table 2). Swaminathan observed the same trend [30].
c. Other factors such as comorbidities or hereditary disorders, severe illness and nutrition may also have increased the prevalence especially in non-thyroidal illness [31].
These factors put together can result in an amalgam of thyroid function abnormalities.
In all, we identified 14 types of thyroid function abnormalities in patients with chronic kidney disease. To make sense of this data, we decided to group them into major and minor disorders. The major types of thyroid dysfunction were subclinical hypothyroidism (4.6%), primary subclinical hypothyroidism (3.6%), primary overt hypothyroidism (1.1%) and Hyperthyroidism (1.1%) ( Figure   2A). Only primary subclinical hypothyroidism was statistically significantly associated with the stages of CKD (p<0.05).However, in our study, the overall hypothyroidism was 9.3%. Similar study was done by Tewari in India who had 10.9% of hypothyroidism affecting the study population [32] but different from Ayree in Ghana who had 2% of hypothyroidism [33]. & Low FT 4 (0.8%) ( Figure 2B).
Low T 3 has been reported in recent literature to be the most frequent type of thyroid dysfunction in patients with CKD [31].
Free and total T 3 and T 4 concentrations are usually normal or low in patients with CKD [33]. This reduction in T 3 concentration has been linked to a decrease in the peripheral conversion of T 4 to T 3 [6]. The drop in the levels of T 3 stimulates the thyroid-pituitary feedback loop, leading to excessive secretion of TSH [35,36]. In some cases the levels of T 3 and T 4 are normalized. Failure of this coping mechanism

Am J Biomed Sci & Res
Copy@ Jules Clement Assob Nguedia will lead to overt hypothyroidism. Furthermore, low T 3 syndrome is closely associated with both malnutrition-inflammation complex syndrome (MICS) and anemia, conditions common in CKD [37]. A Decrease in D1 (de-iodinase) activity caused by the accumulation of uremic toxins, metabolic acidosis, and markers of inflammation such as TNFα, IL-1 results in decreased peripheral conversion of T 4 to T 3 leading to Low T 3 as well as Low FT 3 , accumulation of T 4 , consequently High T 4 and High FT 4 , thus producing the spectrum of minor thyroid dysfunctions seen above [10].
CKD populations had lower albumin and calcium but higher phosphate using linear regression (  (Table 6).

Conclusion
The prevalence of thyroid dysfunction in CKD is very high, with Low T 3 being the most common type. The spectrum of TD is vast.
Low T 3 , Low FT 3 , Hypothyroidism, combine LowT 3 and Low FT 3 are the most common thyroid dysfunction. This study supported the contribution of chronic kidney disease in thyroid dysfunction.
Increased phosphataemia, as well as decreased calcaemia and albuminaemia were identified as predictors of TD in CKD patients.