17th January 2024

Diagnosis

Investigations

• Blood tests are primarily useful for assessing for the complications of sarcoidosis and monitoring on treatment rather than being diagnostic in and of themselves. All patients should have:
  • Full blood count
  • Bone profile (including serum calcium)
  • Liver function tests
  • Urea and electrolytes
  • Serum angiotensin converting enzyme (ACE) level
• 12-lead ECG – important as a baseline screening test for cardiac sarcoid, which most commonly presents with arrhythmia.
• Chest x-ray – essential for the diagnosis of pulmonary sarcoidosis; disease staging is based on radiographic appearance (see table 5). In cases where the clinical and radiological picture is clear cut, the diagnosis can be made based on chest x-ray alone without need for further imaging. Most commonly, there is a symmetrical hilar lymphadenopathy, and if parenchymal involvement is present, it tends to be mid and upper zone predominant nodular or reticulonodular shadowing. Where there is progression to fibrosis, this is upper lobe predominant. Surveillance chest x-ray imaging is used on a 3-monthly basis.
• High-resolution CT chest – can be helpful to further characterise appearances where there is diagnostic uncertainty. It is also more sensitive than chest x-ray, so can be used to detect disease where there is a clinical suspicion in the context of a normal plain radiograph.
• FDG-PET – occasionally used in scenarios of diagnostic uncertainty – looks for active inflammatory disease and is useful for detecting cardiac involvement.
• Pulmonary function testing – can often be normal, but in the presence of fibrosis will show a restrictive lung defect picture.
• Bronchoscopy and biopsy – where there is any diagnostic uncertainty regarding alternative differentials, such as lymphoma and tuberculosis, biopsy is the only way to reach a confirmed diagnosis. On the biopsy sample, a CD4:CD8 ratio >4 in the absence of other inflammatory cells is highly specific for a diagnosis of sarcoidosis.
  • If there are any cutaneous lesions, they can be biopsied in the first instance.
  • Endobronchial ultrasound (EBUS) guided biopsy should be undertaken if there is primarily lymph node disease.
  • Transbronchial biopsies are used if there is primarily parenchymal disease present (4).

Table 5 – Scadding criteria for radiographic staging of pulmonary sarcoidosis

Table 5 Source: Thillai M, Atkins CP, Crawshaw A, Hart SP, Ho L-P, Kouranos V, et al. BTS Clinical Statement on pulmonary sarcoidosis. Thorax. 2020 Dec 2;76(1):4–20.

Image Source: Wikimedia Commons (2016). HilarAdenopathy, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:HilarAdenopathy.png (Accessed: 6 June 2022).