Angiotensin-Converting Enzyme (ACE) is a protein produced primarily by endothelial cells lining blood vessels, particularly in the lungs and kidneys. This enzyme plays an important part in regulating fluid balance and blood pressure. A blood test measures the circulating level of this enzyme, comparing the result against an established reference range. A result below this range can signal several things, ranging from the intended effect of a common medication to an underlying health issue.
The Function of ACE and Reference Ranges
ACE is a component of the Renin-Angiotensin System (RAS), a hormonal cascade that helps manage tension within blood vessel walls. Its main job is to convert the inactive hormone Angiotensin I into Angiotensin II, a powerful compound that causes blood vessels to constrict and raises blood pressure. The enzyme also breaks down bradykinin, a substance that helps widen blood vessels, meaning its overall action promotes higher blood pressure. Reference ranges for ACE levels vary between laboratories, but a result below this established range means the enzyme’s activity is lower than typically seen in a healthy population.
How Medications Affect ACE Levels
The most frequent reason for a low ACE measurement is the use of ACE inhibitors, a class of pharmaceuticals commonly prescribed to manage high blood pressure and heart failure. These drugs are designed to deliberately block the action of the ACE enzyme. By inhibiting ACE, the conversion of Angiotensin I to Angiotensin II is reduced, preventing vasoconstriction. This leads to the relaxation and widening of blood vessels, which lowers blood pressure. Patients taking these medications, often recognizable by the suffix “-pril” (e.g., lisinopril or ramipril), are expected to have a low ACE level, indicating the medication is working as designed.
Medical Conditions Associated with Low ACE
When a low ACE level is detected in a patient who is not taking an ACE inhibitor, it may point toward an underlying health disorder. These pathological causes are less common than medication effects but reflect a disruption in the body’s enzyme production or metabolic processes.
One condition linked to decreased ACE is hypothyroidism, which is an underactive thyroid gland. The resulting reduced metabolic rate can slow down the overall body function, including the production of various enzymes and proteins like ACE.
Certain types of chronic liver disease, such as cirrhosis, may also be associated with lower ACE levels. The liver is a central site for the synthesis of many circulating proteins, and significant impairment of its function can lead to reduced enzyme production.
Furthermore, severe malnutrition or prolonged starvation can lead to a low ACE result. The body’s lack of necessary protein and energy substrates impairs the overall synthesis of enzymes.
Conditions like chronic obstructive pulmonary disease (COPD) and emphysema, which involve extensive damage to the lungs where ACE is highly concentrated, have also been observed to correlate with decreased enzyme activity. A healthcare provider must evaluate the full clinical picture, including a patient’s medical history and current medications, to correctly interpret a low ACE result.