| Value | Category | 
                                    
                    
                        | 1 | Blood taken | 
                                    
                    
                        | 2 | Not present | 
                                    
                    
                        | 3 | Refused | 
                                    
                    
                        | 4 | Sample not tested/lost/damaged/insufficient | 
                                    
                    
                        | 6 | Other | 
                            
            Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.