Background Chronic kidney disease (CKD) and immunosuppression, such as in renal transplantation (RT), stand as one of the established potential risk factors for severe coronavirus disease 2019 (COVID-19). Case morbidity and mortality rates for any type of infection have always been much higher in CKD, haemodialysis (HD) and RT patients than in the general population. A large study comparing COVID-19 outcome in moderate to advanced CKD (Stages 3–5), HD and RT patients with a control group of patients is still lacking. Methods We conducted a multicentre, retrospective, observational study, involving hospitalized adult patients with COVID-19 from 47 centres in Turkey. Patients with CKD Stages 3–5, chronic HD and RT were compared with patients who had COVID-19 but no kidney disease. Demographics, comorbidities, medications, laboratory tests, COVID-19 treatments and outcome [in-hospital mortality and combined in-hospital outcome mortality or admission to the intensive care unit (ICU)] were compared. Results A total of 1210 patients were included [median age, 61 (quartile 1–quartile 3 48–71) years, female 551 (45.5%)] composed of four groups: control (n = 450), HD (n = 390), RT (n = 81) and CKD (n = 289). The ICU admission rate was 266/1210 (22.0%). A total of 172/1210 (14.2%) patients died. The ICU admission and in-hospital mortality rates in the CKD group [114/289 (39.4%); 95% confidence interval (CI) 33.9–45.2; and 82/289 (28.4%); 95% CI 23.9–34.5)] were significantly higher than the other groups: HD = 99/390 (25.4%; 95% CI 21.3–29.9; P < 0.001) and 63/390 (16.2%; 95% CI 13.0–20.4; P < 0.001); RT = 17/81 (21.0%; 95% CI 13.2–30.8; P = 0.002) and 9/81 (11.1%; 95% CI 5.7–19.5; P = 0.001); and control = 36/450 (8.0%; 95% CI 5.8–10.8; P < 0.001) and 18/450 (4%; 95% CI 2.5–6.2; P < 0.001). Adjusted mortality and adjusted combined outcomes in CKD group and HD groups were significantly higher than the control group [hazard ratio (HR) (95% CI) CKD: 2.88 (1.52–5.44); P = 0.001; 2.44 (1.35–4.40); P = 0.003; HD: 2.32 (1.21–4.46); P = 0.011; 2.25 (1.23–4.12); P = 0.008), respectively], but these were not significantly different in the RT from in the control group [HR (95% CI) 1.89 (0.76–4.72); P = 0.169; 1.87 (0.81–4.28); P = 0.138, respectively]. Conclusions Hospitalized COVID-19 patients with CKDs, including Stages 3–5 CKD, HD and RT, have significantly higher mortality than patients without kidney disease. Stages 3–5 CKD patients have an in-hospital mortality rate as much as HD patients, which may be in part because of similar age and comorbidity burden. We were unable to assess if RT patients were or were not at increased risk for in-hospital mortality because of the relatively small sample size of the RT patients in this study.

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Traditional dietary recommendations for patients with chronic kidney disease (CKD) focus on the quantity of nutrients consumed. Without appropriate dietary counselling, these restrictions can result in a low intake of fruits and vegetables and a lack of diversity in the diet. Plant nutrients and plant-based diets could have beneficial effects in patients with CKD: increased fibre intake shifts the gut microbiota towards reduced production of uraemic toxins; plant fats, particularly olive oil, have anti-atherogenic effects; plant anions might mitigate metabolic acidosis and slow CKD progression; and as plant phosphorus has a lower bioavailability than animal phosphorus, plant-based diets might enable better control of hyperphosphataemia. Current evidence suggests that promoting the adoption of plant-based diets has few risks but potential benefits for the primary prevention of CKD, as well as for delaying progression in patients with CKD G3-5. These diets might also help to manage and prevent some of the symptoms and metabolic complications of CKD. We suggest that restriction of plant foods as a strategy to prevent hyperkalaemia or undernutrition should be individualized to avoid depriving patients with CKD of these potential beneficial effects of plant-based diets. However, research is needed to address knowledge gaps, particularly regarding the relevance and extent of diet-induced hyperkalaemia in patients undergoing dialysis.

The importance of phosphate homeostasis in chronic kidney disease (CKD) has been recognized for decades, but novel insights - which are frequently relevant to everyday clinical practice - continue to emerge. Epidemiological data consistently indicate an association between hyperphosphataemia and poor clinical outcomes. Moreover, compelling evidence suggests direct toxicity of increased phosphate concentrations. Importantly, serum phosphate concentration has a circadian rhythm that must be considered when interpreting patient phosphate levels. Detailed understanding of dietary sources of phosphate, including food additives, can enable phosphate restriction without risking protein malnutrition. Dietary counselling provides an often underestimated opportunity to target the increasing exposure to dietary phosphate of both the general population and patients with CKD. In patients with secondary hyperparathyroidism, bone can be an important source of serum phosphate, and adequate appreciation of this fact should impact treatment. Dietary and pharmotherapeutic interventions are efficacious strategies to lower phosphate intake and serum concentration. However, strong evidence that targeting serum phosphate improves patient outcomes is currently lacking. Future studies are, therefore, required to investigate the effects of modern dietary and pharmacological interventions on clinically meaningful end points.

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