Is a serum Angiotensin-Converting Enzyme (ACE) level of 29 considered high or low?

Serum ACE Level of 29: Interpretation

A serum ACE level of 29 U/L is LOW, falling well below the normal adult reference range of approximately 40-150 U/L (or 8-52 U/L depending on the assay method used). 1, 2, 3

Understanding Normal ACE Values

• Normal adult serum ACE activity ranges from approximately 8-52 U/L in most standardized assays, with mean values around 6.05 ± 2.0 units in healthy individuals 2
• ACE levels vary by age and sex: children have higher levels than adults, and males typically have higher levels than females of comparable age 3
• The specific reference range depends on the laboratory assay method used, but a value of 29 would be considered low in most standardized assays 1, 2

Clinical Significance of Low ACE

Low serum ACE levels are associated with several conditions:

• Chronic obstructive pulmonary disease (COPD): ACE levels are significantly reduced compared to control subjects 4, 3
• Lung cancer: Reduced ACE activity is observed 3
• Tuberculosis (active cavitary): Normal to reduced ACE levels 4, 3
• Cystic fibrosis: Significantly reduced levels 3
• Corticosteroid therapy: ACE levels are even lower in patients receiving steroids 3

What This Rules Out

A low ACE level of 29 effectively excludes:

• Active sarcoidosis: Elevated ACE (>11.6 units or >2 SD above mean) is found in 60-70% of patients with active disease, with mean levels of 15.76 ± 7.4 units 1, 2, 3
• Gaucher's disease: Shows markedly elevated ACE levels, often exceeding those seen in sarcoidosis 2
• Silicosis: Demonstrates elevated ACE concentration (646.5 ± 239.1 ng/mL) 4
• Miliary tuberculosis: Shows elevated ACE levels (647.0 ± 217.1 ng/mL), unlike cavitary tuberculosis 4

Important Clinical Context

• ACE is believed to originate from the lungs, so chronic lung disease typically reduces serum levels 3
• Low ACE has no established diagnostic utility for specific diseases, unlike elevated ACE which aids in sarcoidosis diagnosis and monitoring 1, 2
• If sarcoidosis was being considered, this low value argues strongly against active disease, as ACE elevation is a useful confirmatory test when present 1, 3

Key Pitfall to Avoid

• Do not interpret a low ACE level as indicating any specific disease process—it is a nonspecific finding that may reflect chronic lung disease, medication effects (especially corticosteroids), or simply normal variation at the lower end of the reference range 4, 3