Alkaline phosphatase levels charts Explained (in children, adults, & pregnancy)

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Alkaline phosphatase is not a single enzyme. Instead, they are a group of isoenzymes present in different body tissues.

The majority of alkaline phosphatase present in your blood is derived from the liver and bones. However, these two sources are not the only sources of alkaline phosphatase.

Alkaline is present in:

  • The liver.
  • Bones.
  • Intestinal and stomach mucosa.
  • The kidneys.
  • The placenta (its levels markedly increase during the third trimester of pregnancy).
  • Germinal tissues (testicles and ovaries).
  • It is also produced in excess amounts by some cancer cells, such as Hodgkin’sHodgkin’s cells.

The four main causes of elevated alkaline phosphatase are:

  • Bile outflow obstruction from the liver (bile duct obstruction by a stone, tumor, stricture, or infection).
  • Liver diseases.
  • Bone diseases.
  • Some types of cancer.

However, diseases are not the only cause of elevated alkaline phosphatase.

Other benign and physiological conditions may cause increased levels of alkaline phosphatases, such as:

  • Pregnancy.
  • Bone growth (children, young adolescents).
  • Aging (alkaline phosphatase slightly and gradually increase in older ages).
  • And others.

In this article, you will learn the different levels of alkaline phosphatase in:

  • Adults.
  • Children and adolescents.
  • Pregnant women.
  • Low alkaline phosphatase (lower limits by age) and its cause.
  • The common causes of marked versus mild elevations in alkaline phosphatase.

1. Normal alkaline phosphatase levels charts (by age and gender).

The alkaline phosphatase normal ranges in adults range from 44 to 121 U/L (reference). These limits vary slightly from laboratory to laboratory.

In children and adolescents, the levels are often higher (due to bone growth) (reference).

The chart below illustrates normal alkaline phosphatase levels by age and gender (reference).

The vertical, black, and dotted lines represent adults’ upper limit of normal alkaline phosphatase.

alkaline phosphatase levels chart in adults and children

The reference ranges for age and gender is in the table below (according to the famous U.S. Lab (labcorp®)).

alkaline phosphatase reference ranges

The normal adult levels (121 U/L) in males and females may increase either moderately (less than four times the upper limit of normal (ULN)) or markedly (more than four times the ULN).

The causes are summarized in the table below (reference):

Causes of Marked ALP elevations (>600 U/L).

Causes of mild to moderate elevations (<600 U/L)

1. Obstruction of the bile ducts by a gallstone.1. Bone growth (children & adolescents).
2. Other causes of bile duct obstructions (cancers, strictures, infections).2. Pregnancy (third trimester).
3. Liver disease leading to marked bile stasis inside the liver (intrahepatic cholestasis)
– Toxin or Drug-induced cholestasis.
– Primary biliary cholangitis.
– Primary sclerosing cholangitis.
– Metastatic cancer in the liver.
– Infiltration of the liver with T.B, Sarcoidosis, etc.
– Others.
3. liver diseases causing mild cholestasis:
– Hepatitis: alcoholic, viral, or chronic.
– Liver Cirrhosis.
– Early stages of the liver infiltrative disease.
– decreased blood supply to the liver (hypoperfusion).
4. Transient hyperphosphatemia of infancy and childhood.4. Bone diseases.
5. Liver transplant rejection.5. People with blood groups O & B.
6. Total Parentral Nutrition (TPN).6. Some types of cancer.
 7. Others such as thyroid diseases, diabetes, etc.

2. Alkaline phosphatase levels charts in children & young adolescents (0-16 years).

Children and young adolescents have significantly higher levels of alkaline phosphatase.

The elevations of alkaline phosphatase may reach 3 or 4 times the levels in adults.

The cause of significant elevations of alkaline phosphatase in children and young teenagers is bone growth. High bone turnover produces excess amounts of enzymes in the circulation.

The chart below shows the normal alkaline phosphatase levels in children and young adolescents (from 0-16 years) (reference).

Note the black horizontal line that represents the upper limit in adults. This line gives you an idea about the magnitude of elevations in alkaline phosphatase in children and young adolescents compared to adults.

alkaline phosphatase upper limits (children and adolescents).

Transient hyperphosphatemia of infancy and early childhood.

Sometimes, infants and young children (mainly between the ages of 6 months and two years) may experience periods of extreme elevations of alkaline phosphatase.

According to studies, 2-3% of infants and young children may have temporarily marked elevations of alkaline phosphatase (above 1000 U/L).

The exact cause is still unknown. But the condition is often asymptomatic and self-limiting after a few weeks or months.

3. Alkaline phosphatase levels chart during pregnancy (different trimesters).

The placenta produces significant amounts of alkaline phosphatase during pregnancy. As a result, pregnant women often have significantly higher levels.

The changes in prevalence in the last three months of pregnancy are due to larger, fully developed placenta.

In the third trimester, alkaline phosphatase levels up to twice the upper limit of normal (ULN) are considered normal (reference).

One study assessed the average levels of alkaline phosphatase during different trimesters of pregnancy, and here are the numbers:

  • The first trimester: 68.5 U/L on average.
  • The second trimester: 75.9 U/L.
  • The third trimester:
    – 7th month: 126.7 U/L
    – 8th month: 178.8
    – 9th month: 234 U/L.

The chart below shows the dramatic increase of alkaline phosphatase levels during the third trimester of pregnancy (reference)