key: cord-0747175-ojftlxsf
authors: Svetitsky, S; Shuaib, R; McAdoo, S; Thomas, D C
title: Long-term effects of Covid-19 on the kidney
date: 2021-09-17
journal: QJM
DOI: 10.1093/qjmed/hcab061
sha: d05f5527fd64634b332540a603b43d0ab9649554
doc_id: 747175
cord_uid: ojftlxsf

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Finally, Huang et al. describe outcomes 6 months after diagnosis in a cohort of 1733 patients discharged from hospital, of which 4% were admitted to ICU, with low rates of AKI (6%) and no mention of RRT requirement. 9 At follow-up, 13% (107/822) of patients with normal eGFR at the acute phase and without AKI during their admission, were found to have reduced GFR (<90 ml/mi/1.73 m2). However, 29.7% (142/478) of the patients with a reduced eGFR at the acute phase who did not have an AKI as defined in the study were then found to have normal renal function. This may be accounted for by the fact that baseline creatinine was not used to diagnose AKI and thus the diagnosis was inaccurate. Additionally, 8.6% (213/2469) of the original cohort were excluded from the analysis due to various co-morbid conditions; the exclusion of these frailer patients may have led to bias.

The data available are necessarily preliminary and describe outcomes from the early stages of the pandemic. Current, improved management of the disease may help prevent multisystem deterioration leading to renal injury. Conversely, as treatment strategies evolve to enhance patient survival, more patients with co-morbidities recover and are discharged who may have lower potential for long-term recovery of renal function. Another key consideration is that Covid-19 infection has been found to lead to severe weight loss, more severe in patients with reduced renal function. 10 The ensuing sarcopenia may lead to an over-estimation of GFR.

There are multiple ways, pathologically, in which Covid-19 infection could affect the kidney via both the systemic inflammatory response and the effects of critical illness. Direct infection of renal cells has been debated: positive PCR tests of renal tissue have been described, 11 however recent biopsy series have not found evidence of infection using immunohistochemistry or RNA in situ hybridization. Biopsies have shown various findings in addition to the non-specific finding of acute tubular injury. In some patients with nephrotic range proteinuria, collapsing glomerulopathy has been observed. 12 This has been found in patients of African ancestry, and is strongly associated with a high risk APOL1 genotype. An additional repeated finding in biopsy series is thrombotic microangiopathy, found in one series in 6/17 cases and in 2/10 cases in another. 13, 14 A recent study found an increased incidence of anti GBM disease during the first wave. 15 The immediate impact of Covid-19 on patients with preexisting renal disease has been severe, with high mortality rates; 16 analysis of large prospective cohorts of patients that have survived Covid-19, such as the PHOSP-COVID study, will allow us to understand the proportion of all patients who have survived with long-term renal impairment and the risk factors that pre-dispose to it. The integration of genetic and proteomic data from such studies may also identify biomarkers for recovery or chronicity and point to the mechanisms involved.

Conflict of interest. None declared.

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