Numbers of red blood cells and  platelets may be either normal or decreased. Acute kidney injury and low albumin levels in the blood (hypoalbuminaemia) are common. Low blood sodium levels and raised liver enzymes have been reported. Accumulations of fluid in the lungs (pleural effusion), around the heart (pericardial effusion), and in the abdomen (ascites) have also been reported, consistent with generalized inflammation.Differences with respect to Kawasaki disease include frequent presentation with gastrointestinal symptoms such as vomiting, diarrhoea, and abdominal pain. Neurological involvement also appears to be relatively frequent. It often affects older children, whereas Kawasaki disease usually occurs before the age of five. Multiorgan disease appears to be more frequent. Myocarditis and cardiogenic shock seem to be relatively common. Myocarditis may be more evident in older children and adolescents. Preschool children tend to display more Kawasaki-like characteristics. Features of macrophage activation syndrome appear to be more frequent than in Kawasaki disease. Characteristic laboratory findings that are not usually encountered in Kawasaki disease include very high levels of ventricular natriuretic peptide (a marker of heart failure), as well as somewhat lower platelet counts, lower absolute lymphocyte counts, and higher CRP levels. Very high troponin levels (suggestive of myocardial damage) are also common. Clinical course
Clinical course tends to be more severe than with Kawasaki disease. A childs condition can deteriorate rapidly, even in the presence of reassuring laboratory findings. Many children develop shock and heart failure. Most require paediatric intensive care. Supplemental oxygen is often needed, and mechanical ventilation is sometimes used.
Over half (52%) the children with available information had no recorded underlying health condition, including being overweight or obese (among those who did have some comorbidity, 51% were either overweight or obese).Regarding ethnicity, reports from France and the UK raised the possibility that children of Afro-Caribbean descent may be at greater risk, plausibly due to a genetic predisposition. In the US (as of mid-July), the majority of cases were classified as Hispanic/Latino (38%) or non-Hispanic Black (33%) people. Based on reports confined to Europe and the US, the condition seems to affect more children of African, Afro-Caribbean, and Hispanic descent, whereas Kawasaki disease affects more of East Asian and Pacific Islander ancestry. The role of socioeconomic and other environmental factors in such discrepancies is unclear.As regards geographical distribution, there has been uncertainty as to whether the initial reports of cases in Europe and North America reflected a true pattern, or whether the condition had gone unrecognized elsewhere. In Japan and other Southeast and East Asian countries where Kawasaki disease is usually much more prevalent than in Europe, no case of Kawasaki-like disease linked to COVID-19 had been reported during the first wave of transmission. Reports of confirmed or suspected cases have since emerged in many different countries around the world.None of the three main provisional case-definitions  of the emerging entity is diagnostically specific. Concerns have been raised regarding the potential for missed or delayed diagnosis of Kawasaki disease due to heightened diagnostic suspicion for the new entity.