U of U PA School Calcium and Phosphorus

Where is phosphorus stored? What does it do?

Stored in bones as hydroxyapatite

Phosphorylates enzymes

Major intracellular cation in skeletal system

What amount of phosphorus is found in serum?

<1% of total amount

10% of that is bound to albumin

Why are phosphorus deficiencies less common?

Easily absorbed in GI tract from bood

Unbound form freely filtered at glomerulus and PCT

-Able to reabsorb high levels based on need

What can cause a phosphorus deficiency? (5)

Low vitamin D

Extreme starvation

Improper TPN

Refeeding syndrome

Respiratory alkalosis shifts phosphorus intracellularly

What does mild hypophosphatemia cause? Severe?

Mild - well tolerated, mostly asymptomatic

Severe

-Weakness

-Respiratory muscle weakness

-Hemolytic anemia

What are the normal serum levels of phosphourus?

3-4.5 mg/dl

What is the treatment for mild hypophosphatemia? What should be monitored with this?

Oral elemental phosphorus

-Often paired with sodium or potassium

Monitor BMP to avoid hypernatremia or hyperkalemia

What is the treatment for severe hypophosphatemia? What should be monitored with this?

IV dosing of phosphorus

Can cause hypocalcemia

Recheck levels after 6 hours of administration

When is hyperphosphatemia seen? What causes it?

Seen in CKD when GFR <25

Caused by decreased excretion of phosphorus within kidney

-Decreased GFR leads to decreased excretion

What does hyperphosphatemia cause?

Increased mortality and CV events

-Regardless of CKD status

Secondary hyperparathyroidism - renal atrophy in CKD

Phosphorus deposits -> calcification of vasculature

What is secondary hyperparathyroidism?

High phosphate and PTH

Low calcium

Low vitamin D

How does secondary hyperparathyroidism present?

Secondary chronic hypocalcemia

-Elevated phosphorus binds calcium causing decreased serum levels

Presents similarly to CKD

What can hyperparathyroidism cause?

Renal osteodystrophy

Calciphylaxis in CKD

What is the treatment for hyperphosphatemia?

Calcium carbonate to bind excess phosphate and mitigate hypocalcemia

-Give even if normal calcium levels

Sevelamer - PO4 binder

Vitamin D supplementation

What are normal serum total calcium levels?

8.4-10.2 mg/dl

How does hypocalcemia present?

Muscle tetany and neuronal hyperexcitability

-Paresthesias

-Chvostek sign - facial muscle twitch

-Trousseaus sign - wrist flexion with BP cuff

What is the treatment for hypocalcemia? How should it be monitored?

If symptomatic and severe

-IV calcium chloride or calcium gluconate

Reevaluate levels every 6 hours

Monitor electrolyte levels

-Potassium

-Phosphorus

-Magnesium

-Vitamin D

What can treatment for hypocalcemia cause?

Nausea

Hypertension

What is the treatment for asymptomatic or mild hypocalcemia? How should it be monitored?

Oral calcium and vitamin D

If acutely low reevaluate in 24 hours

If chronically low reevaluate weekly

Replace magnesium and potassium as needed

How does hypercalcemia present?

Bones (osteopenia, fractures)

Stones (kidney stones)

Abdominal groans (anorexia, constipation)

psychiatric overtones (weakness, fatigue, altered mental status)

What is the treatment for mild hypercalcemia?

Discontinue meds that can cause it

-Supplements

-Thiazides

-Lithium

What is the treatment for severe hypercalcemia?

NS to expand volume - 1st line

-Give lasix if volume overload

SQ calcitonin

IV bisphosphonates

Glucocorticoids

Why are glucocorticoids used in hypercalcemia?

Decrease intestinal calcium absorption and vitamin D synthesis

What is calciphylaxis? When is it seen most commonly?

Calcific uremic arteriopathy

-Calcium deposits on medial layer of small arteriaes causing small vessel stenosis

Seen in ESRD

What does calciphylaxis cause?

Painful cutaneous lesions due to tissue ischemia and infarct

Can lead to ulcers and infection

How is calciphylaxis diagnosed?

Vessel biopsy

Where does calciphylaxis most commonly affect?

Core adipose reguions

How is calciphylaxis treated?

Discontinue calcium supplements

Supportive wound care

How do loop diuretics affect calcium?

Block NKCC2 leading to increased renal calcium and sodium excretion

Can help in hypercalcemia

How do thiazide diuretics affect calcium?

Block NCC causing increased calcium reabsorption

Can help in hypocalcemia and prevent calcific kidney stones