A balanced view of calcium and
phosphate homeostasis in
chronic kidney disease
Calcium balance in normal individuals and in patients
with chronic kidney disease on low- and high-calcium
diets
Calcium balance in chronic kidney
disease: walking the tightrope
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Here is a suggested answer:
Balance studies are labor-intensive and demanding. Accurate intake and output measurements, steady-state conditions, and a crossover design to exclude individual variability are necessary. Moreover, due to the occasional removal/retention of calcium dialysate in patients receiving dialysis, long-term precise calcium balance research was never possible in dialysis. Recently, the potential use of naturally occurring calcium isotopes could open the door for more understanding of calcium balance in patients with CKD (1).

1- Shroff R, Lalayiannis AD, Fewtrell M, Schmitt CP, Bayazit A, Askiti V, Jankauskiene A, Bacchetta J, Silva S, Goodman N, McAlister L, Biassoni L, Crabtree N, Rahn A, Fischer DC, Heuser A, Kolevica A, Eisenhauer A. Naturally occurring stable calcium isotope ratios are a novel biomarker of bone calcium balance in chronic kidney disease. Kidney Int. 2022 Sep;102(3):613-623. doi: 10.1016/j.kint.2022.04.024. Epub 2022 May 27. PMID: 35644284.
– Probably because balance studies are labor-intensive and demanding.
– Balance studies thus require sufficient equilibration time. (Around 90 days) and accurate measurements of intake and output.
– Balance can be assessed only when patients are in steady state
1-Because balance studies are labor intensive and demanding
2-The participants should be in a steady state to assess the balance
Gold-standard balance studies are scarce in CKD because they are so labor-intensive and so demanding of participants and investigators
These studies are different in timing and follow-up. Short periods of follow-up, not well-documented parameters of ca/P, and the time needed for a steady state of sustained calcium balance is not easy. It is difficult to conduct studies in this field because patients will have many confounding and we need very large numbers in all stages of CKD. Rather we need to adjust for individual variations of the study population’s vitamin D, PTH basal biochemical variables etc.
why the studies on calcium balance in patients with CKD are very limited.1- studies investigating calcium balance in CKD are scant, maby balance studies are labor-intensive and demanding, costy
2-many factors affect these studies Age, bone disease, exersis , different hormones
( hormones such as pth, vid d..,)
3-duration needed to reach equilibrium
4-cant determine actual elemental ca intake and fecal loss
Why the studies on calcium balance in patients with CKD are very limited? Calcium homeostasis is not well understood in CKD patients .
Variety of CKD-MBD which needs specific investigations like isotope and bone biopsy .
Studies on Ca balance are deficient as it is complexed and costly, need time, as Calcium homeostasis is affected by other factors like PTH, vitamin D level, to confirm that pts in neutral calcium balance and normal vitamin d level Before starting, currently no definite time to return to steady state following changes in dietary calcium,
CKD affect intestinal motility mostly has constipation and increased transit time, unethical to expose CKD pts to high Ca diet with susceptible soft tissue calcification
This because Accurate balance can be assessed only after participants have had adequate time to equilibrate into a steady state.
One review of 210 studies suggested that the mean duration when balance was achieved was 90 days.It is unlikely that bone had achieved a steady state within the brief 1-week time span in this study.
Gold-standard balance studies are scarce in CKD because they are so labor-intensive and so demanding of participants and investigators.
management of calcium is complex and need expertises especially that calcium is afffected by many factors is CKD patient because of their comorbidties and medications
calcium balence in CKD is complex, affected by dysregulated hormones that affect calcium absorption, calcium adsorption, and low gfr that affect calcium excretion. inaddition most of ckd already receiving medications affect calcium homestasis
The study on calcium balance are scant because they are labor intensive and are demanding
As the classical calcium balance study the calcium appearant absorption (intake minus the fecal calcium) and net retention (intake minus fecal minus urinary) and corresponding coefficient.
So need for more investigation which is costly.
In my opinion since it needs calcium balance during all stages of CKD patients and balance calcium in dialysis and dietary intake of calcium.
and as the ckd progresses the calcium excretion become less
The Calcium and phosphate
Response to hypocalcemia;
This tight homeostasis is interrupted early in CKD, with resultant secondary hyperparathyroidism and CKD-MBD.
Hill et al;
This study;
needs a long duration of time.
cost effectiveness ( more lab investigation and radiology)
Mostly due to ca in body present by different form and many hormones and factor affecting their level and metabolism also in ckd pt many factors affecting their level and these studies need a lot of money
Why the studies on calcium balance in patients with CKD are very limited.
Studying Ca metabolism is very difficult and needs a steady state for a long duration of time.
As the study conducted by Spiegel and Brady included 6 patients with stage 3 and 4 CKD, although they reached a good and helpful conclusion, there is still an obstacle to taking their findings as given findings especially the steady state of the CA and the duration besides the small number of patient that was involved in the study.
why the studies on calcium balance in patients with CKD are very limited.
1-they are so labor-intensive and so demanding of participants and investigators
2- the best and accurate method for calculation of calcium distribution in tissue is isotoptechnique has limitation
CKD patients have a abnormal calcium metabolism compared to non ckd individuals. Studies are scarce as it hard to set up studies and also to measure intake and output of calcium as well as to define steady state for calcium metabolism.
It might not be cost effective to do a study
Ca homeostasis is not an easy marker to measure in CKD, and studies are lacking for several reasons
Calcium homeostasis is not well understood in patients with chronic renal disease, due to the fact that calcium shortage is a stimulant for secondary hyperparathyroidism and, as a result, bone loss, while calcium excess promotes extraosseous calcifications. so the studies will be difficult to apply.
Understanding calcium balance is particularly important in CKD. However, there is scarcity of calcium balance studies. In your opinion why the studies on calcium balance in patients with CKD are very limited.
Understanding calcium balance is particularly important in CKD. However, there is scarcity of calcium balance studies. In your opinion why the studies on calcium balance in patients with CKD are very limited.
Thanks Dr Omar.
1. measurement of calcium balance can be challenging and requires expertise, what makes it difficult to conduct large studies2.research funding 3. CKD patients have too much comorbidities , what makes it difficult to contribute the effects of calcium alone on outcomes.
Thanks, Dr Nour. Moreover, they need a steady state condition.