Calcium and phosphorus are the most abundant inorganic salts in the human body and are important components of bones and teeth. Why do patients with chronic kidney disease (CKD) experience hypocalcemia? This is because calcitriol, the most important substance affecting calcium absorption, is converted in the kidney from the precursor 25-hydroxyvitamin D3. In CKD, insufficient synthesis of calcitriol leads to inadequate calcium absorption in the small intestine, causing hypocalcemia. Another reason is that hypocalcemia triggers hyperactivation of parathyroid hormone (PTH), which mobilizes calcium from the bones, temporarily increasing free calcium levels — but this is actually a palliative measure. Why do CKD patients experience hyperphosphatemia? The decline in glomerular filtration rate reduces phosphorus excretion, resulting in hyperphosphatemia.
Calcium homeostasis in the body is regulated by parathyroid hormone, calcitriol, and calcitonin. When calcium levels are low, PTH secretion increases, mobilizing calcium release from bones; calcitriol levels increase to stimulate calcium absorption; and calcitonin levels decrease to prevent free calcium from moving into bones and to promote calcium reabsorption.
If hypocalcemia without hyperphosphatemia and iPTH is not elevated: calcium supplementation is needed.
If hypocalcemia without hyperphosphatemia and iPTH is elevated: calcium supplementation plus calcitriol pulse therapy.
If hypocalcemia with hyperphosphatemia and iPTH is elevated: first supplement calcium and reduce phosphorus to 1.78 mmol/L, then calcitriol pulse therapy can be used, because calcitriol may increase phosphorus levels.
If hypocalcemia with hyperphosphatemia and iPTH is not elevated: use calcium acetate with meals to reduce phosphorus, and take calcium carbonate on an empty stomach or before sleep for calcium supplementation.
If hypercalcemia with hyperphosphatemia and iPTH is elevated: first use lanthanum carbonate or sevelamer carbonate to reduce phosphorus, and use cinacalcet to reduce iPTH and calcium (because it acts on calcium receptors on the surface of parathyroid cells, preventing reactive iPTH increase and reducing secondary hyperparathyroidism).
Note: Calcium supplementation may aggravate arterial calcification, so it is not recommended in cases of arterial calcification. Instead, calcitriol can be used to promote calcium absorption.
This is quite insightful. It reminds me of orthopedics, where many patients have osteoporosis and take calcium supplements, but the absorption is poor, leading to hypercalcemia
It should be related to the decline of kidney secretory function. At this time, adjusting to traditional Chinese medicine methods for kidney nourishment may work better (for convenience, commonly used patent medicine like Eucommia ulmoides Bone-Strengthening Granules). Perhaps the kidney-nourishing method plays a role in regulating calcitriol synthesis? This opens up a research idea (haven’t checked the literature yet to see if anyone has done this).
Speaking of calcium and phosphorus metabolism, I also recalled discussing this topic last year during my nephrology rotation with Professor Chen Zhenjie from the nephrology department, as a supplement. https://www.zhihu.com/question/36436732/answer/2598958753?utm_id=0
At this time, high calcium levels but still osteoporosis is firstly due to a decrease in calcitriol content (reduced renal secretion), leading to reduced calcium absorption function; secondly, it is because calcitonin cannot transfer calcium back into the bones and increases calcium reabsorption. Meanwhile, the impact of high calcium on the blood vessels of patients with vascular calcification should also be considered. There are two treatment methods at this stage: one is to use calcitriol to promote calcium absorption (after reducing phosphorus); the other is if the patient is diagnosed with bone pain caused by osteoporosis (only this diagnosis is reimbursed by medical insurance), calcitonin can be used. Traditional Chinese Medicine (TCM) kidney-tonifying is also a method. For patients with high calcium but osteoporosis, TCM kidney-tonifying combined with calcitriol treatment can be compared with calcitriol treatment alone. This could be considered a scientific research approach, haha.
