A pandemia da Covid-19 trouxe desafios ao sistema de saúde em diversas esferas: diagnóstico, tratamento e medidas para evitar a disseminação da doença. Com a maior disponibilização e variedades de testes diagnósticos, torna-se fundamental sua adequada interpretação. Este posicionamento pretende orientar unidades de diálise em relação ao uso de critérios clínicos e testes diagnósticos para a tomada de decisão referente à descontinuação do isolamento de pacientes com suspeita ou confirmação de Covid-19, assim como para o retorno às atividades laborais de colaboradores com suspeita ou confirmação de Covid-19. 
This document intends to help dialysis units regarding the use of laboratory tests for COVID-19, and the use of clinical criteria as tools to aid decision making regarding: 1) ending the isolation of patients with suspected or confirmed COVID -19 and 2) return to the activities of healthcare professionals and employees with suspected or confirmed COVID-19.
These technical recommendations, mostly adapted from the guidelines of the Center for Disease Control and Prevention (CDC -United States of America) 1 , must be adapted for our local context and reality, and depend on the support of public managers, as for example, the availability and financial support to carry out laboratory tests for COVID-19, and to define the flow of collection from regional laboratories. Still, decision-making must be individualized.
Finally, we emphasize the lack of well-established data on virus behavior, the natural history of the disease and test availability. Changes to this document may be necessary due to new information and evidence that may crop up.
Today, we have two types of tests to diagnose COVID-19: RT-PCR and serology, which are available in the usual modes, such as ELISA, Chemiluminescence and Immunochromatography, with antigen and immunoglobulin dosage, in the most diverse combinations (Antigens, Total Antibodies, Immunoglobulins A, M and G) 2 .
The gold standard test in the acute phase for active infection still is RT-PCR (reverse transcription polymerase chain reaction) 3 , which consists of a qualitative or quantitative assessment of viral RNA, collected from two different sites. However, its methodology and complex validation phase make it difficult to carry out this type of test en masse 2 .
Given their low cost, serological tests have a good diagnosis rate in the late phase, in view of the available methodologies, and wide distribution in laboratories (public and private). The essential factor is the time between symptoms onset/contact with a person with a confirmed diagnosis and the test being performed 2 .
Regardless of antibodies showing up in the individual, the ability to measure these antibodies by laboratory methods depends on a series of test characteristics, which make up the test performance, such as analytical sensitivity (detection threshold) and analytical specificity (less interference from other substances or antigens) 3 .
Ten days after the condition onset, immunoglobulin sensitivity (IgA, IgM and IgG) increases progressively, reaching between 79.8% to 94.3%, 4 
After clinical suspicion or laboratory confirmation, ideally the patient should undergo dialysis in an isolation room, following the measures recommended in the "SBN good practices recommendations to dialysis units regarding the epidemic of the new Coronavirus (COVID-19)", described in the flowchart below ( Figure 1) The flowchart below helps on criteria for discontinuing the isolation and other precautions against COVID-19 transmission in the dialysis unit, instituted during suspected (Figure 2 ) or confirmed cases (Figure 3 ), such as, 1) patient wearing a surgical mask 6 , 2) not reuse of lines and dialyzers 6 , 3) dressing with a disposable apron for the healthcare professional in direct contact 6 and 4) the minimum distance of 1 meter 8 . However, we consider it prudent in case the patient is removed from isolation before the end of 14 days, to keep wearing a surgical mask until 14 days after the onset of symptoms 9 . The flowchart defines two strategies: one that considers exclusively clinical criteria, and another which is a laboratory strategy, based on COVID-19 testing. All criteria must be met according to the strategy adopted. The laboratory strategy should be preferable in hospitalized and severely immunodepressed patients 1 .
It should be emphasized that decision-making must be individualized, considering the context, local particularities and clinical perception, sometimes subjective, of the patient.
3. reCommendaTions for healThCare professionals and sTaff wiTh suspeCTed or Confirmed in dialysis uniTs To reTurn To Their aCTiViTies Dialysis staff suspected of having COVID-19, regardless of symptom severity, should be temporarily removed from work. Their return to activities will depend on laboratory diagnostic confirmation and/or clinical evolution (symptoms improvement and fever resolution). The flowchart presented below guides these decisions (Figure 4) , also defining two strategies: one that considers exclusively clinical criteria and another laboratory strategy, based on testing for COVID-19. Again, it is important to stress that the approach must be individualized, and consider the context and local particularities, as well as the epidemiological moment of the pandemic 9 .
This strategy based on clinical criteria can be used in cases with mild symptoms, low suspicion of COVID-19 or if the laboratory test (serology or RT-PCR) is not available 1 . 