Both Phosphorous (P) and Parathyroid Hormone (PTH) are important for healthy bones and their blood levels are regularly monitored for people with stage 5 chronic kidney disease (CKD). Healthy bones contribute to a healthy life, so read on for more information!
Phosphorus is a mineral that is found in many foods and is abundant in the body. It is estimated that 85% of the P found in your body is located in the bones and teeth, making it an important indicator of bone health. PTH is secreted from the parathyroid glands, which are small glands located behind the thyroid gland in your neck and control the body’s calcium and phosphate levels in the blood.
How do P & PTH relate to chronic kidney failure?
When the kidneys are not functioning properly, as in CKD, they don’t produce enough Vitamin D. Vitamin D helps remove excess phosphorous (P) in the body, excessive plasma phosphorous can lead to low blood plasma calcium levels. Low calcium levels trigger the parathyroid glands to make more PTH, if this cycle is repeated enough, the parathyroid glands become hyperactive which leads to secondary hyperparathyroidism (SHPT).
Secondary hyperparathyroidism occurs when the parathyroid glands release too much PTH in the blood.
Note: It is common for people with CKD to have SHPT develop over time, as kidney function declines. Discuss with your nephrologist how best to manage this.
What are the main consequences of high PTH levels?
Bone health issues. Potential fractures, bone and joint pain.
In order to correct for the low plasma Calcium levels, PTH will pull calcium from the bones to compensate, which can result in weakening of the bones, increased bone and joint pain, and can lead to broken bones. This of course will directly affect your day to day life. Dealing with a broken bone on top of dialysis is not a good experience. At the most dangerous levels, observational studies have shown that CKD patients who have values at the extremes (less than 2 or greater than 9 times the upper normal limit of the assay), have an increased risk of death*
What should your P & PTH target levels be when you are on dialysis?
Phosphorus levels should be between 3.5-5.5 mg/dL
PTH levels are recommended to be between 150-300 pg/mL
Please note: The reference range for parathyroid hormone (PTH) is dependent on the type of test used and what it detects. Intact PTH detection is the most widely used assay today, with that said assay kits from different manufacturers measure varying types and amounts of these circulating fragments, comparing different types of tests can lead to inconsistent results. More information from NKF can be found here.
Bottom line on test results:
Keep track of your blood test results. Discuss result ranges with your nephrologist and dialysis center.
Variability in test results are seen between labs, and can be dependent on the actual type of test used (there are multiple manufacturers for different tests).
Keeping track of your test results and knowing your own baseline levels is very important particularly if you travel to other dialysis centers or have a hospital visit.
How to manage and treat secondary hyperparathyroidism (SHPT)?
1. Phosphorous level management
Keep your phosphorus levels between 3.5 - 5.5 mg/dL
Manage your diet by eating foods low in Phosphorous, and don’t cheat as much as you might like to!
Consult your dietician to create diet that works for you
Take phosphate binders with meals (5-10 min before or after) as needed
FYI- Phosphate and phosphorous are often used interchangeably in regards to test results
2. Medication Options: Consult with your physician to determine the best option(s)
Vitamin D mimics or analogs: Zemplar® (paricalcitol) and Hectorol® (doxercalciferol) are two examples. These are provided in both capsule or injection form. Reminder: Active Vitamin D absorbs calcium and decreases release of PTH
Vitamin D supplements (example: calcitriol)
Sensipar® (cinacalcet) decreases PTH production by directly working on parathyroid and decreasing serum calcium. It is taken in pill form
Parsabiv® (IV version of Sensipar) given at end of dialysis treatment via IV 3 times a week. Newest FDA approved treatment (Feb 2017)
Kidney Transplant for those with SHPT - only if the underlying problem cannot be fixed by methods above.
Important Note: PTH testing is only done every 3 months by most dialysis centers, if you find your PTH levels are fluctuating a lot per test result, you can ask for more regular test results. Consult with your nephrologist.
What if PTH levels are too low?
Bone fractures are still a concern. If the intact PTH levels are less than 100 pg/ml, this can result in low bone turnover (also known as adynamic bone disease) and bone weakening and bone fractures can occur. Consult with your physician, and eat phosphorous rich foods. This is one of the only times you will probably get permission to eat badly! Take advantage.
Be proactive, know what your phosphorus and PTH levels are, follow prescribed treatments and avoid food high in phosphorus to help your overall health.