What blood tests are used to diagnose sarcoidosis?

From the Guidelines

Blood tests for sarcoidosis typically include angiotensin-converting enzyme (ACE), complete blood count (CBC), comprehensive metabolic panel, calcium levels, and inflammatory markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) 1. These tests help assess disease activity and organ involvement but cannot definitively diagnose sarcoidosis. The diagnosis typically requires clinical presentation, radiographic findings, and histological evidence of non-caseating granulomas, usually obtained through biopsy. Some key points to consider when ordering blood tests for sarcoidosis include:

• ACE levels are elevated in about 60-80% of patients with active sarcoidosis, though this test isn't specific to the condition 1.
• Hypercalcemia and hypercalciuria may be present due to increased vitamin D production by granulomas 1.
• Liver function tests can detect hepatic involvement, while CBC might show anemia or leukopenia 1.
• Inflammatory markers like CRP and ESR can help assess disease activity 1.
• Blood tests are valuable for monitoring disease progression and treatment response, with decreasing ACE levels often indicating improvement 1. Regular monitoring of these parameters is important for patients on corticosteroids or other immunosuppressive therapies. It's also important to note that there is no definitive test for sarcoidosis other than a positive biopsy, usually endobronchial or from skin, minor salivary glands, or lymph nodes 1. Special stains should be negative for mycobacteria and fungi, and the classic appearance is of a non-caseating granuloma composed of a central area of tightly packed epithelioid, giant cells, CD4+ T cells surrounded by CD8+ T and B lymphocytes and fibroblasts at the periphery. Some other tests that may be included in the diagnosis of sarcoidosis are:
• Pulmonary and cardiopulmonary function tests 1.
• Perfusion studies 1.
• Broncho-alveolar lavage 1.
• ECG 1. However, these tests are not always necessary and should be ordered on a case-by-case basis. In general, the diagnosis and management of sarcoidosis should be guided by clinical presentation, radiographic findings, and histological evidence of non-caseating granulomas, rather than relying solely on blood tests. Therefore, a comprehensive approach that includes clinical evaluation, radiographic imaging, and histological examination is necessary for the accurate diagnosis and management of sarcoidosis 1.

From the Research

Blood Tests for Diagnosing Sarcoidosis

• The serum angiotensin-converting enzyme (sACE) test is commonly used to diagnose sarcoidosis and determine its active status 2, 3, 4.
• The sACE test has a sensitivity of 60% and a specificity of 93% for diagnosing sarcoidosis 2.
• The test also has a positive likelihood ratio (PLR) of 8.4 and a negative likelihood ratio (NLR) of 0.43 2.
• Measuring sACE can assist in the diagnosis of sarcoidosis, but the interpretation of the results should be done with caution 2, 5.
• Elevated serum ACE activity is found in 60-70% of sarcoidosis patients, but extremely elevated ACE activity can be suggestive of familial hyperactivity of ACE, a benign condition 6.
• ACE can also be measured in bronchoalveolar lavage fluid (BAL) and cerebrospinal fluid (CSF) to diagnose sarcoidosis with extra-pulmonary locations 4.

Limitations of Blood Tests

• The sensitivity and specificity of high ACE for diagnosis of sarcoidosis are not perfect, with a sensitivity of 41.4% and a specificity of 89.9% in one study 5.
• The positive predictive value (PPV) and negative predictive value (NPV) of high ACE for diagnosis of sarcoidosis are 25.4% and 94.9%, respectively 5.
• The diagnostic utility of ACE is limited, and it should be used in conjunction with other clinical, biological, and radiological arguments to diagnose sarcoidosis 5.