Phosphate

Question 1

Distribution of phosphate in the body

Answer 1

80% in bone; 20% in soft tissue; <1% in serum/plasma (round 30% is inorganic phos.)

Question 2

Functions of phos

Answer 2

Component of DNA and RNA, coenzymes, reservoirs of energy, indirectly affects oxygen release from hgb.

Question 3

Where does phos come from in the blood?

Answer 3

Absorbed in the intestine from diet, released from cells into blood, loss from bone to blood.

Question 4

How is phos regulated in the body?

Answer 4

By renal excretion or re-absorption

Question 5

How is phos regulated by the kidneys?

Answer 5

• PTH: increases renal excretion (lowers blood levels)
• Vit D: increases absorption in intestine, reabsorption in kidney (incr. blood level)
• Acid-base status
• Calcitonin: stimulates excretion (sends phos + Ca back to bone)
• Excess GH: helps reg. bone growth, increases blood level by decreasing renal excretion.

Question 6

What can result from hypophosphatemia?

Answer 6

ATP depletion

Question 7

20-40% of patients with what disorders are likely to have hypophosphatemia?

Answer 7

Diabetic ketoacidosis, COPD, asthma, malignancy, inflammatory bowel disease, anorexia nervosa, alcoholism.

Question 8

Hypophosphatemia can also be caused by:

Answer 8

• Increased renal excretion

- Decreased intestinal absorption

Question 9

What is the mortality rate in patients with severe hypophosphatemia?

Answer 9

30%

Question 10

What causes hyperphosphatemia?

Answer 10

• Hypoparathyroidism
• Increased intake
• Increased release of cellular phosphate (severe infection, intensive exercise, neoplastic disorders, lymphoblastic leukemia, intravasular hemolysis)

Question 11

What are the samples to determine inorganic phosphorous?

Answer 11

Serum/lithium heparin plasma (oxalate, citrate, EDTA plasma interfere)

Question 12

What interfers with testing?

Answer 12

Hemolysis; because there is a higher [ ] in the cells it would be increased
Prolonged storage

Question 13

How does the circadian rhythm affect phosphorous testing?

Answer 13

• Highest levels in late morning

- Lowest levels in the evening

Question 14

Which type of urine is best for testing inorganic phosphorous?

Answer 14

24hr due to diurnal variation

Question 15

How is inorganic phosphorous measured colorimetrically?

Answer 15

• There is a formation of ammonium phosphomolybdate complex

- Measured by UV at 340nm or reduced to molybdenum blue and read at 600-700nm

Question 16

Reference ranges for phosphate

Answer 16

Serum:

• Neonate: 1.45-2.91
• child <15: 1.07-1.74
• Adult: 0.78-1.42

Critical: <0.33 >3.00

24hr urine: 13-42mmol/day

Question 17

How do calcium and phosphate relate?

Answer 17

Inversely:
Increased Ca-decreased phos
Decreased Ca-increased phos