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Alkaline Phosphatase (ALP) — Pregnancy Reference Values

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Alkaline phosphatase (ALP) — serum

Serum ALP increases progressively during pregnancy due to production of placental alkaline phosphatase isoenzyme. Levels in late pregnancy may rise 2–4× above nonpregnant values.

Units Nonpregnant Adult 1st Trimester 2nd Trimester 3rd Trimester
U/L 33 – 96 17 – 88 25 – 126 38 – 229
µkat/L 0.55 – 1.6 0.28 – 1.47 0.43 – 2.1 0.63 – 3.82
Causes of elevated alkaline phosphatase
  • Physiologic in pregnancy
    • Placental alkaline phosphatase production (major determinant)
    • Bone turnover from fetal skeletal development
  • Hepatobiliary disorders
    • Intrahepatic cholestasis of pregnancy (ICP)
    • Obstructive biliary disease
    • Primary biliary cholangitis
    • Primary sclerosing cholangitis
    • Infiltrative liver disease (sarcoidosis, amyloid, TB, fungal)
    • Cirrhosis
    • Hepatic metastases
  • Bone-related disorders
    • Paget disease
    • Healing fractures
    • Osteomalacia / rickets
    • Osteogenic sarcoma
    • Bone metastases
    • Hyperparathyroidism
  • Endocrine / systemic
    • Hyperthyroidism
    • Acromegaly
    • Leukemia / myelofibrosis
  • Pregnancy-associated conditions
    • Severe preeclampsia with hepatic involvement
    • HELLP syndrome

Placental ALP is typically responsible for very high ALP levels late in pregnancy. In contrast, a disproportionate rise in GGT or bilirubin suggests cholestasis or liver disease.

Causes of low alkaline phosphatase
  • Hypophosphatasia (primary cause; genetic ALPL deficiency)
  • Other causes
    • Hypothyroidism
    • Magnesium deficiency
    • Zinc deficiency
    • Malnutrition / protein-calorie deficiency
    • Pernicious anemia
    • Severe anemia or chronic systemic illness
    • Certain genetic variants affecting ALP activity
  • Pregnancy interpretation
    • Low ALP is unusual and should prompt evaluation for nutritional deficiency or hereditary hypophosphatasia.

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.
  3. Fischbach FT. Manual of Laboratory and Diagnostic Tests, 7th ed.
  4. Mornet E. Hypophosphatasia. Orphanet J Rare Dis. PMID: 17107627.