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What Is An Alkaline Phosphatase Test?

Find out how alkaline phosphatase is measured and what it means for your thyroid.
What Is An Alkaline Phosphatase Test?
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Navigating the various blood tests related to your thyroid function can be challenging. While some tests are straightforward, like a thyroid-stimulating test and free T4, others that impact your thyroid function but do not directly measure it can be complicated. Here is what you need to know about an alkaline phosphatase test related to your thyroid function.

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What is an alkaline phosphatase test?

Alkaline phosphatase (ALP) is an enzyme found in a pregnant person's liver, digestive system, bones, kidneys, and placenta. Enzymes are a specific type of protein that helps your body carry out certain functions. We have thousands of enzymes in our bodies that serve various purposes, and we can measure several of them to learn about a person's health status. 


An alkaline phosphatase test is most often used to check if a person has liver disease or a bone disorder. If the levels are high, it may indicate you have a disease in either of these organs, or it may also mean there has been damage to the liver.


Symptoms of liver disease include:

  • Nausea and vomiting
  • Weight loss
  • Tiredness
  • Weakness
  • Jaundice
  • Swelling or pain in your abdomen
  • Dark-colored urine and/or light-colored stool
  • Frequent Itching


Symptoms of bone disorders include:

  • Pain in the bones or joints
  • Enlarged and/or abnormally shaped bones
  • Increased frequency of bone fractures


Two different tests look at alkaline phosphatase. For an overall assessment of ALP levels, your healthcare provider may order a general ALP level, which is usually a part of liver function tests or a comprehensive metabolic panel (CMP) that looks at other markers like glucose, albumin, bilirubin, creatinine, other liver enzymes, and electrolytes like sodium and potassium. 


The other form of testing this marker is through an alkaline phosphatase isoenzymes test, which can tell you what organs produced the ALP. This second ALP test provides more information, but it is often more expensive and complicated to interpret. 

Why your healthcare provider may order an alkaline phosphatase test


An alkaline phosphatase test can be part of your routine health workup, especially when it is included in a comprehensive metabolic panel. However, your doctor may also order it to see if you have a problem with your liver or bones. And, if you are acutely ill, your healthcare provider will also order this test regularly and monitor these enzyme levels.


An ALP test (along with other liver enzymes) will not necessarily diagnose any medical condition. Still, it will allow your health care provider to watch for patterns in both your blood tests and symptoms. By tracking these levels, your doctor can put together a clearer picture of your overall health status and do other testing and assessments to determine what may be causing problems.


What is the normal range for ALP?

The reference range for lab tests varies from laboratory to laboratory based on the laboratory that processes your blood sample. However, your results should say if the value is within the normal range or is high or low, and your healthcare provider will also confirm the results.

Reference ranges are based on the average values in a population, which means that a reference range does not take into account the clinical picture of a patient but is simply the average values and standard deviations of adults in an area. You should work with a health care provider who can interpret your results and determine action steps accordingly. 


High ALP Levels

As mentioned above, high alkaline phosphatase levels may certainly indicate liver damage or bone disease. Examples of liver damage that may raise ALP include:

  • Liver cirrhosis
  • Hepatitis
  • Obstruction or stricture of the bile ducts
  • Cholestasis in pregnancy
  • Mononucleosis (often referred to as "mono")


Other causes of elevated ALP levels include:

  • Bone metastasis
  • Osteomalacia
  • Hyperparathyroidism
  • Hyperthyroidism
  • Untreated celiac disease


Slightly elevated levels may be caused by various reasons--some of which are entirely normal. For example, mildly elevated ALP levels are standard in pregnant people, people healing from a broken bone, and children and adolescents undergoing bone growth and development. Your age and your sex can also impact your alkaline phosphatase level. For example, men generally have slightly higher ALP levels than women, and it is common in older adults. Finally, certain medications like birth control pills and diet can influence these liver enzymes.


Low ALP levels

While it is more common to have an elevated alkaline phosphatase level, you may also have a low alkaline phosphatase level. Low alkaline phosphatase levels may be a sign of malnutrition or deficiencies in key minerals like zinc and magnesium, and it also may be a sign of hypothyroidism

How does ALP affect thyroid function?


The liver plays an essential role in supporting the chemical processes of making thyroid hormones. Your liver needs to be healthy for proper thyroid hormone conversation. 

Your thyroid gland makes two thyroid hormones: thyroxine (T4) and triiodothyronine (T3). T4 is the inactive form of thyroid hormone, and it needs to be converted into T3 to be used by the cells. Most T4 is converted to the active T3 in the organs--primarily, the liver. Therefore, it can throw off thyroid function and thyroid hormone levels when the liver is not functioning appropriately. 


Intriguingly, research in the Journal of Gastroenterology and Hepatology also suggests that untreated hypothyroidism can cause liver problems over time.


We often see thyroid-binding globulin and thyroxine levels become elevated when liver disease is present. Hepatitis C may also cause thyroid abnormalities, as can using interferon therapy to treat liver diseases. Some research shows that thyrotoxic patients also have elevated ALP levels, suggesting that excess thyroid hormone may cause liver damage


The thyroid and the liver are intricately interconnected, and both organs need to be healthy to support optimal health. Therefore, if you have a suspected thyroid problem, it may be helpful for your doctor regularly check your liver function.


Likewise, if you have a known liver problem, you and your doctor should carefully watch your thyroid function to be sure that it is working optimally. You can track your thyroid function with an at-home complete thyroid panel test mailed directly to you from Paloma Health. 

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Julia Walker, RN, BSN

Clinical Nurse

Julia Walker, RN, BSN, is a clinical nurse specializing in helping patients with thyroid disorders. She holds a Bachelor of Science in Nursing from Regis University in Denver and a Bachelor of Arts in the History of Medicine from the University of Colorado-Boulder. She believes managing chronic illnesses requires a balance of medical interventions and lifestyle adjustments. Her background includes caring for patients in women’s health, critical care, pediatrics, allergy, and immunology.

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