You must use OEM filters because they’re specifically engineered to meet the 1.5 cmH2O/L/s resistance limits required for accurate spirometry. Third party filters often vary in resistance by 15 percent or more, which can lead to false positive results for restrictive lung disease. These specialised filters provide a 99.99 percent viral and bacterial filtration efficiency rating. Using non-certified parts may also void your 2 year manufacturer warranty and compromise patient hygiene standards.