7 Causes of Slightly Elevated Alkaline Phosphatase (160, 170, 180, 200 U/L, etc.)

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A slightly elevated alkaline phosphatase level is caused by either physiological conditions (such as pregnancy, growing bones, or aging). It is also caused by disease conditions such as liver, biliary, bone, thyroid diseases, some cancers, etc.

The normal reference range of alkaline phosphatase in adult males and females is between 44 and 121 U/L (reference).

Slight variations between labs in the reference ranges are often present. Check the normal reference range provided by your lab.

Slight alkaline phosphatase (ALP) elevations refer to values just above the upper limit of normal (150, 160, 170, 180 U/L, etc.

Also, ALP values up to twice the upper limit of normal (121*2 = 242) are considered slight elevations.

The marked elevation is a term that describes alkaline phosphatase levels that are more than 4 or 5 times the upper limit of normal.

The table below summarizes the causes of slightly elevated alkaline phosphatase levels ( 160, 170, 200, or up to twice the upper limit of normal) (reference).

causes of slightly elevated alkaline phosphatase levels

Physiological causes of slightly elevated alkaline phosphatase.

1. People with blood groups (B) or (O).

The alkaline phosphatase is an enzyme in a wide variety of tissues. Commonly, it is found in bones and the liver.

Also, the gastrointestinal tract (particularly the small intestine) is abundant in ALP.

Normally, the intestinal alkaline phosphatase enters the bloodstream after eating. But it rapidly binds to your red blood cells, so its levels do not increase.

NOTE: blood tests detect ALP that is free in the bloodstream (serum), not the ALP bound to red blood cells.

In people with blood groups (B) and (O), the red blood cells are less capable of binding the intestinal ALP reaching the bloodstream.

As a result, those people may experience slight elevations in serum alkaline phosphatase after eating.

The elevations are more noticeable after eating high-fat foods. And the levels often return to normal after they eat.

Symptoms & diagnose:

The condition is completely benign without any symptoms.

To diagnose your condition, your doctor will fulfill the following criteria:

  • Absence of symptoms of liver, biliary, and bone disease.
  • Isolated ALP increases (other lab tests are normal such as liver enzymes, bilirubin, etc.).
  • Repeat testing while fasting (ALP often returns to normal).

The elevation in ALP is often mild (160-200). However, it may reach more than 300 U/L (reference).

2. Growing infants, children, and young adolescents.

Alkaline phosphatase is present in abundance in bones. Therefore, alkaline phosphatase often increases during bone growth and bone formation.

That’s why the reference ranges of alkaline phosphatase vary significantly in children and adolescents.

A slight elevation in ALP is normal in infants, children, and growing adolescents.

The chart below illustrates the significant differences in infants, children, and adolescents compared to the adult levels (reference).

alkaline phosphatase levels chart in children and young adult

3. Aging.

People who get older (often those in their 50s, 60s, and older) have slightly elevated alkaline phosphatase levels (reference).

Slight elevations of alkaline phosphatase such as 160 or 170 U/L can result from advancing in age.  

4. Pregnancy.

Alkaline phosphatase is found in the placenta. Therefore, you may experience slight enzyme elevations during pregnancy during the first two trimesters.

In the third trimester, alkaline phosphatase levels rise significantly due to the presence of a fully-formed large placenta.

The upper limit of normal alkaline phosphatase is up to twice that of normal (121 in non-pregnant adults).

The rise is completely asymptomatic. And doesn’t need any further investigations in the third trimester unless:

  • The rise is more than twice the upper limit of normal.
  • You have symptoms such as severe itching, yellowish skin or eye whites, or right upper abdominal pain.

The chart below shows the average alkaline phosphatase levels during pregnancy (reference). Note the significant rise during the third trimester.