Kidney Disease and the Bones

Fragile; handle with care

I had dearly missed renal nursing. I was dying back to go back to the field . Time and again I looked at my papers and gazed at my previous work station and wondered when the sun would shine. It did and I got an opportunity to be in a renal department.

In Kenya, Nephrology/Renal nursing is comprehensive. It involves all facets of renal care to incorporate acute kidney injury and chronic kidney disease. Renal nurses get trained in all therapies or renal replacement. Understandably, we do not practice all of them. The most common ones are kidney transplant and hemodialysis.

That is why I was exhilarated to be placed in a dialysis unit at the new work station. I am getting impressed on a daily basis by the modalities of care some of which I only learnt in books. Care of the failing kidneys is one of the most fulfilling roles a nurse can ever take up.

After such a long break from renal nursing, it was pure serendipity to have one of my Facebook followers ask me what was wrong with his uncle because he has been getting bone problems while on dialysis.

It took me back to one of my patients in Nairobi. He had started hemodialysis at some decrepit private unit for an year before transferring to our newly established renal unit. He had since suffered poor mobility and couldn’t walk without crutches.

The relationship between our kidneys and the bones is an interesting one. Bones have many components top of which is Calcium. That is why the commercial taunts milk and other products as being a source of calcium for strong bones and teeth. That doesn’t mean strengthening teeth and bones are the only roles of calcium.

Without calcium, however, we get brittle bones which easily fracture. Our bodies absorb calcium from the small intestines. This is one source of calcium for our body cells. It is dependent on having sufficient calcium in our food which will be absorbed if we have sufficient blood flow in the gut.

However, this calcium cannot be absorbed without the presence of Vitamin D. Vitamin D from our diet must be in an active form for it to help in this role. The kidneys activate this Vitamin D. I hope I have not lost you.

When we have end stage kidney disease (where we are already on dialysis) this vital function of the kidneys is diminished. That means we do not have an active form of Vitamin D which will encourage our gut to absorb calcium to take to the kidneys.

Further, there is a close knit fellowship between Phosphate and Calcium. They have an opposite relationship. Let me explain. Over 85% of Phosphate is found in bones. It is important in different roles in the body part of which is making muscles contract together with other minerals.

The problem is that if Phosphate is too high in the body, it forms deposits in the body organs. It also causes bone and muscle problems. Now, kidneys regulate this balance of phosphate by secreting them in urine. That way we do not have too little or too high levels of this element.

In end stage renal disease, the kidneys do not make much urine and in other cases they do not make any urine at all. That leaves our levels of Phosphate at dangerously high levels. Our risk for heart attacks and strokes are increased. Our bones become even weaker.

I hope you can see that in this case we already have two mechanisms which are causing bone problems. That takes me to the third one.

There are four tiny weeny glands the size of a grain of rice on your neck. They are behind the big butterfly-shaped one called the thyroid gland. We all know something about the thyroid gland I suppose. If you have come across the word ‘goitre’ then you have surely handled the thyroid gland.

Let’s try something. Go to the mirror. Expose your beck if you have a scarf on. Do you see the voice box? Okay you may not if your neck is as well fed as mine. Ha ha. If you are a man, your thyroid gland is just below the Adam’s apple.

Which reminds me; men that have visible Adam’s apple are God’s gift to the universe. Favourite sons of the creator. Movers and shakers of my all things female. An Adam’s apple invites me to touch it or simply nibble at it. Yes I need prayers thank you.

I’m advertising this my other side. Folks, we start charging in mid-September. Also note it is NOT academic writing. Just speeches.

On the front part of your windpipe is where the thyroid gland is. It is shaped like a butterfly with two lobes. We will call them wings because yes we can.

Show me your butterfly

On the reverse side of this important gland, on every tip of the wings, we have other even smaller glands called the Parathyroid glands. As you can see from the diagram above, we have four tips of the thyroid gland. I mean, each of the two wings has two tips. One for the upper part and another for the lower part. That is for each wing. So we end up with four tips. Ask me to explain if this isn’t clear.

On the reverse side, each tip has a parathyroid gland embedded onto it. When we discuss Calcium and Phosphate, we must pay maximum respect to these four glands.

They look like mustard seeds don’t they? And so the Good Book says,” if you have faith the size of a mustard seed...”

Parathyroid glands produce a hormone called parathormone abbreviated as PTH. PTH is crucial for the regulation of calcium in our body. When calcium levels are low, PTH is secreted (released) by our parathyroid glands.

What PTH does is encourage bones to release the stored Calcium in form of calcium ions into the bloodstream. This, friends and family is the second source of Calcium. One is by our diet where the calcium is absorbed in the gut. The other is from bones under the influence of PTH. We could loosely say bones are our banks. They hold Calcium for us like banks hold money, and dish it to us in small doses should we need it.

When we talk about Vitamin D activation in the kidneys, there are two chemical steps involved. The first one is under the influence of this hormone we are calling PTH.

Excretion (removal from the body) of both calcium and phosphate is through urine and also being deposited (stored) in the bones. It is a cycle I know. Release, absorb, excrete, absorb. Repeat. Most body processes are cycles. This is because we must get things under control. Not too high and not too low. Just like the baby’s chair in Goldilocks’ story, we need everything to be just right.

When kidneys fail, we need to find a way to replace these metabolic and regulatory roles. We do so by administering Calcium and activated forms of Vitamin D supplements. We have medications that come as a combination of both to eliminate the need for multiple tablets.

The patient we had handled was never given these vital supplements and that explained his bone issues.As aforementioned in end stage kidney disease, there tends to be low calcium levels. What happens is that parathyroid glands continue to secrete PTH which draws calcium from the bones to the bloodstream.

Our tiny weeny glands do not know that the kidneys have failed. They sense a low Calcium in the blood and tell themselves that we need Calcium in the blood so we must release PTH to tell the bones to release the Calcium it has in store.

Remember we need calcium for other things not just healthy bones. This function ends up making already weak bones even weaker. A recent calcium supplement contains activated Vitamin D, calcium, and also prevents the parathyroid gland from releasing PTH.

That way we not only get free ions of Calcium in the blood to act on heart muscles and other cells, but also maintain the bound calcium in our bones. That is a win-win for the bloodstream and the bones.

We must look for a mechanism that will ensure that the body does not absorb too much phosphorus from the diet. This is where Phosphate binders come in. These tablets swallowed with food or snacks take ahold of the phosphorus found in our food and prevent it from being absorbed by the body. That way we do not end up with hyperphosphatemia (too much Phosphate in the blood).

Hemodialysis itself is another explanation for weak bones. When a patient’s blood is going through the artificial kidney (dialyser) it can easily clot. That would mean losing a lot of blood. Normally our bodies contain numerous substances to ensure that blood does not clot as it flows through our blood vessels.

One of the most important body’s natural anticoagulant is heparin. This substance is produced by the liver and stored in many cells of the body. It ensures that blood does not clot. What renal nurses do therefore is inject artificial heparin into the blood tubes on the dialysis machine to make sure that blood does not clot.

One of the side effects of this artificial heparin is weakening of bones or what we call osteoporosis. That is why advanced countries have migrated from the good old heparin and adopted a low molecular weight heparin form.

The latter ensures that heparin is administered but not continuously throughout the session of dialysis. That way we achieve anticoagulation without increasing the risk of osteoporosis.

We can improve the outcomes of patients with end stage renal disease by giving appropriate supplements. This goes hand in hand with monitoring laboratory values of the blood. Further, for everyone else whose kidneys are functional, I hope this will make you want to take better care of your kidneys. Stay hydrated.

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