OVERVIEW

What is hypophosphatemia?

Hypophosphatemia refers to a condition where blood phosphorus levels fall below 0.8 mmol/L (equivalent to 2.5 mg/dL).

If blood phosphorus drops below 0.32 mmol/L (equivalent to 1 mg/dL), it is classified as severe hypophosphatemia.

Hypophosphatemia can result from insufficient phosphorus intake, excessive phosphorus excretion, or phosphorus shifting into cells. Symptoms may include irritability, confusion, muscle weakness and pain, nausea, and vomiting. Treatment involves addressing the underlying cause and phosphorus supplementation.

Is hypophosphatemia common?

Hypophosphatemia is not uncommon and can occur in people of all ages and genders. Severe hypophosphatemia is relatively rare.

SYMPTOMS

What are the symptoms of hypophosphatemia?

Mild to moderate hypophosphatemia may have no discomfort symptoms. Severe hypophosphatemia can cause discomfort symptoms, including:

• Neurological symptoms: Irritability, mental disturbances, and in more severe cases, stupor or coma.
• Muscle symptoms: Muscle weakness and muscle pain.
• Hematological symptoms: Reduced immunity and susceptibility to bleeding.
• Gastrointestinal symptoms: Loss of appetite, nausea, and vomiting.

What other diseases can hypophosphatemia cause?

Severe hypophosphatemia can lead to metabolic encephalopathy, heart failure, respiratory failure, intestinal obstruction, and rhabdomyolysis. Additionally, long-term hypophosphatemia may cause rickets and osteomalacia.

Can hypophosphatemia cause sequelae?

Long-term hypophosphatemia may result in rickets and osteomalacia, leading to joint swelling, hunchback, pigeon chest, bow legs, bone pain, limping, muscle weakness, impaired cardiopulmonary function, and even loss of mobility.

CAUSES

What are the causes of hypophosphatemia?

There are three main causes of hypophosphatemia:

• Phosphorus shifts from the blood into cells: Commonly seen in patients with diabetic ketoacidosis or nonketotic hyperosmolar syndrome, alcoholics, and hyperparathyroidism patients after parathyroidectomy (i.e., "hungry bone syndrome").
• Inadequate phosphorus intake or reduced intestinal absorption: Often occurs in patients with insufficient phosphate intake combined with chronic diarrhea/steatorrhea, vitamin D deficiency, or preterm infants exclusively breastfed.
• Increased urinary phosphorus excretion: Frequently observed in patients with hyperparathyroidism, X-linked hypophosphatemic rickets, or Fanconi syndrome.

Additionally, severe burns, post-transplant status, rapid large-volume fluid infusion, diuretic use, and intravenous iron supplementation can also lead to hypophosphatemia.

Is hypophosphatemia hereditary?

A very small proportion of hypophosphatemia cases are hereditary, such as X-linked hypophosphatemic rickets.

Is hypophosphatemia contagious?

No.

DIAGNOSIS

What tests are needed for hypophosphatemia?

Hypophosphatemia can be diagnosed simply by checking blood phosphorus levels. A blood phosphorus level < 0.8 mmol/L indicates hypophosphatemia.

However, merely diagnosing hypophosphatemia is insufficient—it is crucial to identify the underlying cause. Therefore, the following additional tests are required:

• Blood tests: Electrolytes, osmolality, blood glucose, blood ketones, vitamin D, parathyroid hormone, kidney function, creatine kinase, blood gas analysis, etc.
• Urine tests: Urine protein, urine ketones, 24-hour urinary phosphorus/calcium, etc.
• Imaging tests: Including bone X-rays, parathyroid ultrasound, etc.

TREATMENT

Which department should I visit for hypophosphatemia?

Endocrinology or General Internal Medicine.

How is hypophosphatemia treated?

• Addressing the cause: Identifying and treating the underlying cause is essential for curing hypophosphatemia. Some patients may recover spontaneously after the cause is resolved without additional treatment.
• Phosphorus supplementation:
• Mild hypophosphatemia (serum phosphorus 0.64–0.8 mmol/L): Increase phosphate intake through dietary adjustments, such as consuming more dairy, fish, and nuts.
• Moderate to severe hypophosphatemia (serum phosphorus < 0.64 mmol/L): In addition to dietary changes, oral phosphate supplements like potassium phosphate or sodium phosphate may be used. Patients with severe symptoms and serum phosphorus < 0.32 mmol/L may require intravenous sodium phosphate solution.

What are the common side effects of hypophosphatemia medications?

The primary medications for hypophosphatemia are phosphate salts, such as sodium phosphate and potassium phosphate. Oral phosphate supplements rarely cause side effects, but intravenous phosphate therapy may lead to complications like hypocalcemia, kidney failure, or life-threatening arrhythmias.

To avoid severe side effects, doctors monitor serum phosphorus levels every 6 hours. Once levels reach 0.48 mmol/L, treatment is switched to oral phosphate supplements.

Does hypophosphatemia require hospitalization? What should be noted during hospitalization?

Patients with severe symptoms and serum phosphorus < 0.32 mmol/L require hospitalization for intravenous phosphorus supplementation.

During hospitalization, patients should cooperate with doctors for necessary tests and frequent blood draws during phosphorus replacement therapy.

DIET & LIFESTYLE

What should patients with hypophosphatemia pay attention to in their diet?

• Reduce or avoid alcohol consumption.
• Increase intake of phosphate-rich foods such as milk and dairy products, fish, dried shrimp, sunflower seeds, pine nuts, sesame seeds, almonds, etc.

Does hypophosphatemia affect fertility?

Hypophosphatemia can affect fertility because the phosphorus required by the fetus is entirely supplied by the mother. It is recommended to actively treat the underlying condition, correct hypophosphatemia as soon as possible, and plan pregnancy after recovery.

Does hypophosphatemia affect daily activities such as exercise or high-altitude travel?

Short-term hypophosphatemia can be quickly resolved with treatment and does not affect daily activities. However, long-term hypophosphatemia leading to rickets or osteomalacia may impair physical mobility. If cardiopulmonary function is compromised, high-altitude travel is also not advisable.

PREVENTION

Can hypophosphatemia be prevented?

• Maintain a diverse and balanced diet.
• Avoid excessive alcohol consumption.
• Actively treat conditions such as chronic diarrhea, steatorrhea, hyperparathyroidism, and vitamin D deficiency.
• In addition to breastfeeding, premature infants should supplement essential nutrients under medical guidance.
• Diabetic patients should maintain good blood sugar control.