Week 4 Interpreting Common Labs: Ca, Mg, PO4, and Liver Function Tests Flashcards
Forms of Calcium in serum
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%)
What influences Calcium serum levels?
Hypoalbuminemia and acidemia influence serum levels
* Need to correct for hypoalbuminemia ( >35 g/L) for bound calcium (NOT ionized calcium)
Serum levels and causes with hypocalcemia
< 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
Serum level and causes of hypercalcemia
> 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
Treatment for hypo- and hypercalcemia
- 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
Forms of Mg in the body
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%)
Hypomagnesimea levels and causes
< 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
Assessing Mg status
Can measure 24 hour magnesium excretion or fractional clearance
* serum levels not necessarily predictive of severity of symptoms
Mg deficiency treatment
- usually prefer oral supplementation (15-20 mmol)
- May need to consider parenteral replacement: 25 mmol-one bolus is typically insufficient to correct deficits
Mg toxicity levels and causes
Typically in serum levels > 1.2 mmol/L (but rare)
* Renal tubule acidosis may be a cause (occurs with acute or chronic renal failure)
Normal phosphorous status
0.87 – 1.80 mmol/L (higher in children)
* PTH and Vitamin D important in maintaining over all balance in body
Hypophosphatemia levels and causes
typically defined serum <0.97 mmol/L
* re-feeding syndrome
* respiratory alkalosis
* increased insulin administration
* hyperparathryoidism
Treatment for hypo- and hyperphosatemia
- Hypo: 0.48-0.72 mmol/L
- Hyper: use of phosphorus binding agents: calcium carbonate.
Hyperphosphatemia levels and causes
> 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
Liver biochemical tests
- Aminotransferases: markers of hepato-cellular function (ALT and AST)
- Lactic acid dehydrogenase (LDH)
- Liver synthetic function
AST and ALT normal values
- ALT: < 40 U/L)
- AST: <36 U/L (specifically found in liver , heart, skeletal muscle, kidney, pancreas and RBC)
Lab assessment of LDH
45-85 U/L is normal
Interpretation of AST/ALT
- 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
Tests for cholestasis
- 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
What are alkaline phosphatase and gGT?
- 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
