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Angiotensin Converting Enzyme (ACE) — Pregnancy Reference Values

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Angiotensin converting enzyme (serum)

ACE activity is generally **lower in pregnancy** due to physiologic renin–angiotensin–aldosterone activation and reduced pulmonary endothelial ACE expression. ACE is not a routine pregnancy test; interpretation should always consider the clinical context.

Units Nonpregnant Adult 1st Trimester 2nd Trimester 3rd Trimester
U/L 9 – 67 1 – 38 1 – 36 1 – 39
Pregnancy physiology
  • ACE is primarily produced by pulmonary endothelial cells.
  • Pregnancy increases RAAS activity but lowers circulating ACE activity.
  • ACE is **not** a reliable marker of RAAS activation in pregnancy.
  • Ace levels generally remain low-normal across all trimesters.
Causes of elevated ACE
  • Granulomatous disease
    • Sarcoidosis (classic association; limited sensitivity/specificity)
    • Tuberculosis, leprosy, histoplasmosis, other granulomatous infection
    • Silicosis
  • Pulmonary, liver, or hematologic disease
    • Chronic pulmonary inflammation or interstitial lung disease
    • Cholestatic liver disease
    • Certain leukemias or lymphomas
  • Endocrine or metabolic conditions
    • Hyperthyroidism
    • Diabetes mellitus
  • Pregnancy-specific note
    • Values near or above nonpregnant limits are **not** typical — evaluate for nonpregnant causes.

Elevated ACE is not diagnostic for sarcoidosis; imaging and tissue sampling are often required.

Causes of low ACE
  • Medications
    • ACE inhibitors (contraindicated in pregnancy)
    • Some ARBs and renin-angiotensin antagonists
  • Pulmonary disorders
    • Advanced emphysema/COPD
    • Reduced pulmonary endothelial mass (e.g., after lung resection)
  • Systemic disease
    • Advanced liver disease
    • Hypothyroidism
    • Rare inherited low-ACE variants
  • Pregnancy-related note
    • Values in the low range are common and usually physiologic.
    • Marked suppression should prompt evaluation for medications or systemic illness.

References

  1. Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.
  2. Wallach J. Interpretation of Diagnostic Tests. 8th ed. Lippincott Williams & Wilkins.
  3. Fischbach FT, Dunning MB. Manual of Laboratory and Diagnostic Tests. 7th ed.