Inorganic Phosphorus/Bicarbonate

Inversely related

What is the relationship between phosphorus and calcium?

85% in bones, 15% in ECF

Where is phosphorus mainly found in the body?

Organic phosphate (intracellular) and inorganic phosphate (blood buffer)

In what forms does phosphorus exist?

Jejunum

Where is phosphate maximally absorbed?

Required for insulin-mediated glucose entry via phosphorylation

Why is phosphate important in glucose metabolism?

Potassium

What ions enter cells along with glucose?

Acts as a buffer

What is the role of inorganic phosphate in blood?

• Free: 55%

• Complexed: 35%

• Protein-bound: 10%

What are the forms of phosphate in blood?

55%

Free inorganic phosphate

35%

complexed inorganic phophate

10%

Protein bound phosphate

2.7–4.5 mg/dL

Normal phosphorus level in adults?

4.5–5.5 mg/dL

Normal phosphorus level in children?

Hyperphosphatemia and hypophosphatemia

What are conditions of abnormal phosphate levels?

What happens in phosphate deficiency?

ATP depletion

Transcellular shifts

What is a major cause of hypophosphatemia?

PTH, calcitonin, growth hormone

What hormones affect phosphate levels?

Yes

Is fasting required for phosphate testing?

To prevent inaccurate results

Why should serum be separated immediately?

Fiske-Subbarow method (ammonium molybdate)

Method for phosphate determination?

Intracellular cation

What type of ion is magnesium?

4th most abundant cation
2nd abundance to potassium

Magnesium rank in abundance in the body?

Bones

Where is most magnesium stored?

Enzyme activator

What is magnesium’s role in enzymes?

Maintains structure of DNA, RNA, ribosomes

Role in genetic material?

Important in transmission

Role in neuromuscular function?

Role in the heart?

Regulates potassium movement across myocardium

Decreased cellular K+ (faulty Na-K pump)

What happens when Mg is low?

Vasodilation, decreases uterine hyperactivity

What is magnesium’s effect in eclampsia?

55%

Ionized (free) Mg

30%

Protein-bound Mg

15%

Complexed Mg

1.2–2.1 mEq/L

Normal magnesium level?

• AAS

• Calmagite

• Formazan dye

• Methylthymol blue

• Dye-lake method

Methods for magnesium determination?

2nd most abundant ECF anion

What is bicarbonate?

90%

What % of total CO₂ is bicarbonate?

Main role of bicarbonate?

Major blood buffer

Exchange of bicarbonate and chloride to maintain neutrality

What is the chloride shift?

usable buffer

What does bicarbonate convert CO₂ into?

Decreases by 6 mmol/L/hour

What happens if sample is left uncapped?

ISE, enzymatic

Methods for bicarbonate measurement?

21–28 mEq/L

Normal bicarbonate level?

Difference between measured cations and anions

What is the anion gap?

Unmeasured anions vs unmeasured cations

What does it reflect?

Increased acidity (metabolic acidosis)

What does high anion gap indicate?

What does low anion gap indicate?

Decreased acidity

Quality control for electrolyte analyzers

Why is anion gap important in lab tests?