Phosphates are the naturally occurring form of phosphorus and are the second most abundant element in the human body after calcium. Like calcium, phosphates to require Vitamin D for its absorption. However, an abundance of phosphorus in Chronic Kidney Disease patients poses a serious concern as it lowers the calcium levels in the blood and can cause many other health ailments like cardiovascular calcification, metabolic bone disease and the development of secondary hyperparathyroidism (SHPT), etc.
Generally, phosphate is absorbed from digested food in the gut and in normal circumstances if there is higher than normal phosphate absorption, the kidneys are somehow able to cope with increased excretion. But if the kidney function gets hampered, even moderately raised phosphate absorption can lead to “hyperphosphatemia”. And that’s why the patients on dialysis are commonly seen affected with hyperphosphatemia.
What is Hyperphosphatemia?
Hyperphosphatemia is a condition commonly seen among Chronic Kidney Disease (CKD) patients, in which phosphate levels shoot up abnormally high. This can result from varying factors like increase in phosphate intake, decrease in phosphate excretion, or a disorder that shifts intracellular phosphate to extracellular space, but the health of our kidneys plays a crucial role as it is the kidneys that control the amount of phosphate in the blood.
Secondly, phosphate absorption can also be increased with Vitamin D which can lead to hyperphosphatemia through increased gut absorption of phosphate.
Some of the possible causes of hyperphosphatemia due to excessive phosphate intake include:
- Intravenous injection of phosphate
- Excessive intake of Vitamin D through diet or supplements, etc.
- Acute phosphorus poisoning
- Milk-alkali syndrome
What causes Hyperphosphatemia?
If the elimination of phosphate through the kidneys is diminished, especially when there is a high intake of phosphate in foods, Hyperphosphatemia may occur. This can be seen with kidney problems such as acute or chronic renal failure. Parathyroid hormone (PTH) secreted by the parathyroid gland also contributes to the regulation of phosphate. However, when PTH levels are low, then there is increased re-absorption of phosphate leading to retention (called Hypoparathyroidism).
Some of the possible reasons for Hyperphosphatemia due to decreased elimination of phosphate include:
- Kidney failure
- Magnesium deficiency
- Excess consumption of Vitamin D
- Use of bisphosphonates for osteoporosis treatment
- Multiple Myeloma
What are the signs and symptoms of Hyperphosphatemia?
Occasionally patients with Hyperphosphatemia report Hypercalcaemic symptoms such as muscle cramps, numbness or tingling. Other symptoms may include bone or joint pain, rashes, etc. More commonly, patients report symptoms related to the underlying cause of the hyperphosphatemia but these generally are uremic symptoms, such as fatigue, shortness of breath, anorexia, nausea, vomiting, disturbed sleep, etc.
How to diagnose Hyperphosphatemia?
Hyperphosphatemia is diagnosed with specific blood tests which measure the levels of:
- Blood urea nitrogen
- Vitamin D
- Parathyroid hormone (PTH)
How can Hyperphosphatemia be treated?
It is important to diagnose and find the underlying cause of Hyperphosphatemia so as to treat and restore normal phosphate metabolism. Various medications can help normalize the phosphate levels in the blood. Dietary modification or consuming a low-phosphorus diet is also necessary, especially in the case of kidney patients.
How can diet modification help in controlling Hyperphosphatemia?
A low-phosphate diet is an important part of the treatment and management of Hyperphosphatemia. Dietary change alone might be sufficient to restore blood phosphate levels, provided the kidneys are functioning efficiently.
Foods that should be strictly avoided, or at the least consumed in moderation include: manufactured drinks and foods such as soft drinks, chocolates, tinned milk, processed meat, processed cheese, ready-to-eat meals, ice creams, soups containing large quantities of beans, lentils, peas and milk, all of which are high in phosphorus.
Also, vegetables and legumes like asparagus, beans, broccoli, corn, mushroom, pumpkin, spinach, sweet potato, etc. should be consumed in restricted quantity.
Even foods like meat, fish, soft cheese (cottage cheese, mozzarella, etc.) should not be consumed more than one serving a month. However, it is advisable to consult a Nephrologist or renal dietician before making any major diet modifications or changes.
Multiple strategies can be implemented to control phosphate homeostasis in patients with CKD. Besides dietary restriction, removal of phosphates via dialysis or intensive (nocturnal or short daily) dialysis regimens can also be implemented. This modality of treatment also often proves beneficial.
The author, Dr. Sudeep Singh Sachdev, is a Consultant Nephrologist at Narayana Superspeciality Hospital, Gurugram.