Alkaline phosphatase above or below normal: causes in athletes and what to do

A deviation of alkaline phosphatase from the reference range is one of the frequent findings in an athlete's biochemical panel. Most often something harmless lies behind it: growth, injury healing, or a fatty breakfast before the test. Yet sometimes a changed ALP becomes the first clue to cholestasis, a micronutrient deficiency, or energy depletion. The editorial team examines the typical causes of deviation in both directions and offers a logic for action.

First — rule out technical causes

Before looking for a disease, it is worth checking the conditions under which the test was taken. Food, especially fatty food, can raise the intestinal ALP fraction in some people, which is why blood is drawn on an empty stomach. If the sample was taken after breakfast, it is reasonable simply to repeat the test under proper conditions.

The second technical trap is different laboratories. Reference limits depend on the method, and a result of 125 U/L in one laboratory may be normal, while in another it is a slight excess. To assess trends, tests should be done in one place.

The third trap is age. For adolescents and young people who have not finished growing, the standard “adult” norm does not apply. High ALP in a 15-year-old athlete is an expected physiological value, not a pathology.

Finally, small one-off deviations (up to 10–20% beyond the limit) without symptoms and without changes in other markers often have no clinical significance. It is enough to recheck them after a few weeks.

Causes of elevated alkaline phosphatase

Elevated ALP is conventionally divided into bone and liver causes. A bone source is typical of active growth, healing of fractures, including stress fractures, and also of conditions with accelerated bone turnover. Among them are vitamin D deficiency with secondary hyperparathyroidism and osteomalacia.

A liver source is most often linked to cholestasis — impaired bile outflow. The cause may be gallstones, inflammatory diseases of the bile ducts, and also medications. Cholestatic damage has been described, in particular, with the use of oral 17-alpha-alkylated anabolic steroids.

• Bone: growth in adolescents, fracture healing, vitamin D deficiency, hyperparathyroidism, Paget's disease.
• Liver: gallstone disease, drug-induced cholestasis, inflammatory duct diseases, fatty liver disease.
• Other: pregnancy, intake of fatty food, hyperthyroidism, some tumors.

In athletes it is worth mentioning separately the effect of intense training. Studies show that after heavy strength load AST, ALT, and creatine kinase rise sharply, while GGT remains stable. ALP changes little in this case, so its significant elevation should not be written off as a “hard workout”.

Causes of reduced alkaline phosphatase

Low ALP occurs less often, but it is precisely this that often goes unnoticed. One common cause is a shortage of zinc and magnesium, cofactors of the enzyme. In athletes with a restricted diet, high sweat losses, or a vegetarian diet without a well-thought-out plan, such a situation is possible.

The second group of causes is energy and protein deficiency. With chronically low energy availability, bone formation decreases, and with it the bone ALP fraction. This is one of the laboratory features of RED-S syndrome, alongside changes in thyroid and sex hormones.

The third group is endocrine and drug-related factors. Reduced ALP is described in hypothyroidism, and also against the background of certain drugs, for example estrogen-containing preparations and glucocorticoids. Antiresorptive therapy for osteoporosis also lowers markers of bone turnover.

A rare but important cause is hypophosphatasia, a hereditary disease with a mutation in the tissue-nonspecific ALP gene. It manifests as persistently low enzyme activity, bone pain, poorly healing fractures, and early tooth loss. Persistently low ALP with no obvious cause is a reason to discuss this diagnosis with a doctor.

Follow-up workup algorithm

The logic of action for any deviation is the same: first repeat the test under proper conditions, then determine the source of the enzyme. The key step is assessing GGT. A parallel rise in ALP and GGT points to the liver, while an isolated rise in ALP points rather to bone.

If a bone cause is suspected, the doctor may order a separate bone ALP test, the markers P1NP and CTX, and also assess vitamin D and parathyroid hormone. If there is bone pain against the background of training, imaging is appropriate to rule out a stress fracture.

In the case of a liver cause it is important to tell the doctor honestly about all drugs and supplements, including unlicensed ones. This determines whether rare diseases will be sought or whether it will be enough to stop taking the toxic substance and monitor the values over time.

Treating ALP on your own with supplements without finding out the cause is not advisable. Taking zinc or vitamin D makes sense only with a confirmed deficiency, and an excess of zinc by itself can disrupt copper metabolism.

When to see a doctor urgently

Most ALP deviations do not require emergency care, but some combinations of symptoms call for a prompt consultation. These include yellowing of the skin and sclera, dark urine, pale stool, skin itching, and pain in the right upper quadrant.

Immediate examination is also needed for localized bone pain that worsens during exercise and does not go away at rest, especially in runners and players of team sports. These are the classic signs of a stress fracture.

• jaundice, dark urine, discolored stool;
• severe skin itching without a rash;
• persistent bone pain that does not disappear at rest;
• very high ALP (several times above normal) in an adult.

You should also see a doctor if ALP deviates persistently over several tests even without symptoms. Systematic monitoring makes it possible to notice in time both liver and bone disorders that develop slowly.

Athletes who use prescription drugs should remember that tests are only part of monitoring. The absence of complaints does not mean the absence of damage to the liver or other organs.

Editorial conclusions

Alkaline phosphatase above or below normal is not a diagnosis but a clue to where to look next. In athletes it is most often physiological causes or the conditions of testing, but persistent deviations require a search for the source.

The most useful tool is combining ALP with GGT, bilirubin, mineral metabolism markers, and a dietary assessment. This approach makes it possible to notice cholestasis, micronutrient deficiency, or energy depletion in time.

For a deeper understanding of the topic, the editorial team offers materials on what the alkaline phosphatase test shows, on bone turnover markers in athletes, and on relative energy deficiency syndrome RED-S.

References

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