page_title: ILO Classification
section_title: Methodology
hierarchical_section_title: ILO Classification / Methodology
caption_attribution_description: English: Chest X-ray/ILO Classification 2-2 S-S/close-up
context_page_description: The ILO International Classification of Radiographs of Pneumoconioses is a system of classifying chest radiographs for persons with a form of pneumoconiosis. The intent is to provide a standardized, uniform method of interpreting and describing abnormalities in chest x-rays that are thought to be caused by prolonged dust inhalation. In use, it provides a system for both epidemiological comparisons of many individuals exposed to dust and evaluation of an individual's potential disease relative to established standards.
context_section_description: In the current ILO Classification system, the reader is first asked to grade radiographic quality. There are four technical grades: (1) Good; (2) Acceptable, with no technical defect likely to impair classification; (3) Acceptable, with some technical defect but still adequate; and  (4) Unacceptable. Quality defects include over- or under-exposure, underinflation, artifacts, improper positioning, and others.
  Parenchymal Abnormalities: 
  Small Opacities: The reader will categorize small opacities according to shape and size. The small, rounded opacities are p (up to about 1.5 mm), q (about 1.5 mm to about 3 mm), or r (exceeding about 3mm and up to about 10 mm). Small, irregular opacities are classified by width as s, t, or u (same respective sizes as for small, rounded opacities).
  Lung Zones: Each lung is mentally subdivided by the reader into 3 evenly spaced zones: upper, middle, and lower. The zones in which the small parenchymal opacities appear are recorded.
  Profusion: Using the Standard X-rays, the profusion (concentration) of small opacities is classified on a 4-point major category scale (0, 1, 2, or 3), with each major category divided into three, giving 12 ordered subcategories of increasing profusion: 0/-, 0/0, 0/1, 1/0, 1/1, 1/2, 2/1, 2/2, 2/3, 3/2, 3/3, and 3/+. Category 0 refers to the absence of small opacity and category 3 represents the most profuse. The major category (first number) represents the profusion felt to best fit the subject x-ray, and the minor category (second number) represents either the profusion seriously considered as an alternative, or if none, the same profusion as the major category. For example, if the reader thinks the x-ray being read has profusion most like the standard x-ray for category 1, but serious considered category 2 as an alternative description of the profusion, then the reading is 1/2.
  Large opacities: A large opacity is defined as any opacity greater than 1 cm in diameter. They are classified as Category A (for one or more large opacities whose combined longest dimension does not exceed about 50 mm), category B (for one or more large opacities whose combined longest dimension exceeds 50 mm  but does not exceed the equivalent area of the right upper lung zone), or category C (for one or more large opacities whose combined longest dimension exceed the equivalent area of the right upper lung zone).
  Pleural Abnormalities:
  Pleural abnormalities are reported with respect to type (pleural plaques or diffuse pleural thickening), location (chest wall, diaphragm, or other), presence of calcification, width (only of in profile pleural thickening seen along the chest wall edge), and extent (combined distance for involved chest wall).
  Any Other Abnormality:
  There are 29 "obligatory" symbols representing important features related to dust diseases of the lungs and other etiologies. These symbols are: aa atherosclerotic aorta; at significant apical pleural thickening; ax coalescence of small opacities; bu bulla(e); ca cancer; cg calcified granuloma or lymph node; cn calcification of small pneumoconiotic opacities; co abnormal cardiac shape or size; cp cor pulmonale; cv cavity; di marked distortion of an intrathoracic structure; ef pleural effusion; em emphysema; es eggshell calcification; fr  rib fracture(s); hi enlargement of non-calcified hilar nodes; ho honeycombing; id ill-defined diaphragm border; ih ill-defined heart border; kl septal (Kerley) lines; me mesothelioma (pleural). pa plate atelectasis; pb parenchymal bands; pi pleural thickening of an interlobar fissure; px pneumothorax; ra rounded atelectasis; rp rheumatoid pneumoconiosis; tb tuberculosis; and od  other disease or significant abnormality. Finally, the reader comments on any other abnormal features of the chest radiograph or other relevant information.
caption: Close-up right lower zone 2/2 S/S
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