Week 4 Interpreting Common Labs: Ca, Mg, PO4, and Liver Function Tests

Question 1

Forms of Calcium in serum

Answer 1

Protein bound or total calcium (40%)
* 2.20 -2.70 mmol/L

Ionized (50%)
* 1.18-1.29 mmol/L (capillary)
* 1.14-1.29 mmol/L (venous)

Complexed to anions (10%)

Question 2

What influences Calcium serum levels?

Answer 2

Hypoalbuminemia and acidemia influence serum levels
* Need to correct for hypoalbuminemia ( >35 g/L) for bound calcium (NOT ionized calcium)

Question 3

Serum levels and causes with hypocalcemia

Answer 3

< 1.85 mmol/L
* Hypoparathryoidism
* ↓ 1,25 (OH)-vitamin D production (renal or liver disease)
* Malignancies of prostate and breast
* Acute Pancreatitis
* Often coincident with hypomagnesemia

Question 4

Serum level and causes of hypercalcemia

Answer 4

> 2.70 mmol/L (3-4 mmol/L; severe)
* Primary Hyperparathryoidism
* Malignancy (bone)
* Thiazide diuretics
* Granulomatous disease (e.g., sacroidosis, TB, leprosy)
* Excess thyroid hormone
* Excessive vitamin D supplementation

Question 5

Treatment for hypo- and hypercalcemia

Answer 5

• Hypo: IV administration of 15 mg/kg over 4-6 hrs (elemental calcium will ↑ total serum Ca by 0.5-0.75 mmol/L)
• Hyper: treatment depends on causes

Question 6

Forms of Mg in the body

Answer 6

Normal body content: 100 mmol
Normal serum concentration: 0.70-1.0 mmol/L
* Plasma (free (50-70%)
* bound to albumin (20-35%)
* bound to anions (8-10%)

Question 7

Hypomagnesimea levels and causes

Answer 7

< 0.5 mmol/L
* Hypocalcaemia + hypokalemia commonly occur at the same time
* May have normal or low PTH (? PTH resistance)
* Medications can cause hypo-magnesiumia (e.g immunosuppressive therapy such as tacrolimus)
* Other causes: renal diuresis, DM with glycosuria, renal disease with magnesium wasting, hypophosphatemia, hyperthyroidism, alcoholism,
* RFS

Question 8

Assessing Mg status

Answer 8

Can measure 24 hour magnesium excretion or fractional clearance
* serum levels not necessarily predictive of severity of symptoms

Question 9

Mg deficiency treatment

Answer 9

• usually prefer oral supplementation (15-20 mmol)
• May need to consider parenteral replacement: 25 mmol-one bolus is typically insufficient to correct deficits

Question 10

Mg toxicity levels and causes

Answer 10

Typically in serum levels > 1.2 mmol/L (but rare)
* Renal tubule acidosis may be a cause (occurs with acute or chronic renal failure)

Question 11

Normal phosphorous status

Answer 11

0.87 – 1.80 mmol/L (higher in children)
* PTH and Vitamin D important in maintaining over all balance in body

Question 12

Hypophosphatemia levels and causes

Answer 12

typically defined serum <0.97 mmol/L
* re-feeding syndrome
* respiratory alkalosis
* increased insulin administration
* hyperparathryoidism

Question 13

Treatment for hypo- and hyperphosatemia

Answer 13

• Hypo: 0.48-0.72 mmol/L
• Hyper: use of phosphorus binding agents: calcium carbonate.

Question 14

Hyperphosphatemia levels and causes

Answer 14

> 1.80?
* Exogenous phosphorus load in GI tract (vitamin D overdose)
* decreased urinary excretion secondary to renal failure
* cellular release (tumor lysis syndrome)
* acidosis
* Hypocalcaemia can follow

Question 15

Liver biochemical tests

Answer 15

• Aminotransferases: markers of hepato-cellular function (ALT and AST)
• Lactic acid dehydrogenase (LDH)
• Liver synthetic function

Question 16

AST and ALT normal values

Answer 16

• ALT: < 40 U/L)
• AST: <36 U/L (specifically found in liver , heart, skeletal muscle, kidney, pancreas and RBC)

Question 17

Lab assessment of LDH

Answer 17

45-85 U/L is normal

Question 18

Interpretation of AST/ALT

Answer 18

• NAFLD: ALT/AST ratio > 1; typically not reflective of disease severity; typically ALT in 40-100 U/L; high levels do not necessarily mean more severe disease!
• Alcoholic Liver Disease: ALT/AST ratio < 1; gGT may be predictive of severity of liver disease
• Viral Hepatitis: low rise in AST/ALT. Serum levels more indicative of disease severity.
• Fulminant Liver Failure: acute increases in AST/ALT: > 1000-2000 U/L

Question 19

Tests for cholestasis

Answer 19

• Alkaline phosphatase 25-100 U/L
• gGT; g-glutamyltransferase female <75 U/L; male 55 U/L
• Measures of serum total, conjugated, unconjugated and delta bilirubin < 17 μmol/L (total)
• Serum bile acids (Fasting: < 1.3 μmol/L; Post-prandial < 5.5 μmol/L)
• Urinary and biliary bile acid analysis

Question 20

What are alkaline phosphatase and gGT?

Answer 20

• alkaline phosphatase: enzyme found in lining in GI tract; several parts of the body; Zn-dependent protein-consider growth
• gGT; gamma-glutamyltransferase: enzyme in liver; bile duct paucity