Alkaline Phosphatase (ALP) Unit Converter
Alkaline Phosphatase (ALP) Unit Converter
Convert alkaline phosphatase between U/L, IU/L, µkat/L and nkat/L, with adult ranges and the bone-versus-liver question.
Alkaline Phosphatase (ALP) converter
Activity unitsALP 88 U/L
Formula and conversion factor
U/L = µkat/L × 60
- U
- 1 unit = 1 µmol of substrate converted per minute
- kat
- 1 katal = 1 mol of substrate converted per second
- ÷ 60
- the only difference between the two is per-minute versus per-second
- IU/L
- numerically identical to U/L
Worked example
ALP 88 U/L
88 ÷ 60 = 1.467 µkat/L
= 1467 nkat/L = 88 IU/L
Separating the source
| ALP | GGT | Likely source |
|---|---|---|
| Raised | Raised | Hepatobiliary |
| Raised | Normal | Bone, or pregnancy |
| Raised in a child | Normal | Growth — physiological |
| Low | — | Hypophosphatasia, zinc deficiency, malnutrition |
What ALP measures
Alkaline phosphatase is a family of isoenzymes rather than a single protein. In adults the circulating activity comes mainly from liver and bone in roughly equal measure, with smaller contributions from intestine, kidney and, in pregnancy, placenta. The first question about any raised ALP is therefore which tissue it came from.
Gamma-glutamyl transferase answers it in most cases. GGT is present in biliary epithelium but not in bone, so a raised ALP with a raised GGT points to a hepatobiliary source, while a raised ALP with a normal GGT points to bone — Paget disease, osteomalacia, healing fracture, bone metastases, or simply adolescent growth.
Physiological elevations are common and important not to over-investigate. ALP is two to three times the adult limit through the pubertal growth spurt, rises through the third trimester of pregnancy from placental production, and increases modestly after a fatty meal in people of blood groups B and O. In the other direction a persistently low ALP is easy to overlook and can be the only clue to hypophosphatasia, and also occurs in zinc deficiency, malnutrition and Wilson disease.
Frequently asked questions
How do I convert ALP from U/L to µkat/L?
Divide by 60. An ALP of 88 U/L is 1.467 µkat/L.
How do I tell liver ALP from bone ALP?
Check GGT. It is present in biliary epithelium but not bone, so a raised ALP with a raised GGT indicates a hepatobiliary source and with a normal GGT a bone source. Bone-specific ALP can be measured directly if needed.
Why is ALP high in children?
Growing bone produces large amounts of it. Values two to three times the adult upper limit are normal during the pubertal growth spurt and need no investigation in a well child.
What does a low alkaline phosphatase mean?
It is easy to miss but can matter. Consider hypophosphatasia, zinc or magnesium deficiency, malnutrition, hypothyroidism and Wilson disease.
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References
- Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18–35.
- IFCC reference procedure for alkaline phosphatase at 37°C.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.