Questions and Answers
What does an increased serum bilirubin indicate?
What is the significance of total serum bilirubin amount >40 mg/dl?
What is the importance of urine bilirubin and urobilinogen in differential diagnosis of jaundice?
What is the main function of transaminases?
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Which of the following is NOT a contributing organ to alkaline phosphatase in normal serum?
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What is the main source of alkaline phosphatase during childhood?
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What is the effect of magnesium ions on alkaline phosphatase?
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What is the significance of estimating AST and ALT enzymes in serum?
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Where are AST and ALT enzymes present in high concentrations?
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What happens to AST and ALT enzymes in urine unless a kidney lesion is present?
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Study Notes
Uric Acid Concentration in Serum and Urine
- Uric acid levels are affected by exercise and diet containing purine
- Normally, uric acid is excreted through urine, and increased levels in blood are accompanied by increased excretion in urine
- Uric acid levels are increased in several diseases, including:
- Renal failure
- Leukemia
- Multiple myeloma
- Lymphoma
- Glycogenesis
- Chronic hemolytic anemia
- Pernicious anemia
- Lymphosarcoma
- Gout (up to 6.5-12 mg/dl), where uric acid is deposited as crystals in joints
Estimation of Total Calcium in Serum and Urine
- Calcium is the most abundant mineral cation in the body, making up 1-1.5 kg of total body weight in adults
- About 50% of total plasma calcium exists in ionized form, which is functionally most active
- Calcium binds to negatively charged sites on proteins, which is pH dependent
- Ionized and citrate-bound calcium is diffusible from blood to tissues, while protein-bound calcium is not
- Clinical significance:
- Hyperparathyroidism: increased calcium levels, particularly ionized serum calcium
- Hypocalcemia: more serious and life-threatening condition than hypercalcemia
- Rickets: decreased product of serum calcium and phosphorus (usually below 30 mg/dl), with increased alkaline phosphatase activity
Estimation of Inorganic Phosphorus in Serum and Urine
- Phosphorus has two forms: organic (present in soft tissues, proteins, lipids, and nucleic acids) and inorganic (phosphates of alkaline and alkali earth metals)
- Inorganic phosphorus is present in serum and is measured
- Phosphorus is present in four forms in the blood:
- Inorganic phosphorus (H2PO4 and HPO4-2)
- Organic or ester phosphorus (including glycerophosphates, nucleotide phosphate, hexose phosphate, etc.)
Estimation of Total Cholesterol in Serum
- Cholesterol is a precursor of:
- Vitamin D
- Steroid hormones
- Bile acids
Estimation of Total and Direct Bilirubin in Serum
- Bilirubin is formed from heme in reticuloendothelial cells and is then transported to the liver, where it is conjugated to produce bilirubin monoglucuronide and diglucuronide
- Conjugated bilirubin is water-soluble and excreted through bile
- Bilirubin is reduced to urobilinogen in the intestine, which is then recycled through the body and excreted through urine
- Clinical significance:
- Hemolytic jaundice: increased unconjugated bilirubin due to increased destruction of red blood cells
- Hepatic jaundice: decreased conjugated bilirubin and decreased excretion of bilirubin
- Posthepatic jaundice (obstructive jaundice): increased conjugated bilirubin compared to unconjugated bilirubin
- Total serum bilirubin >40 mg/dl indicates hepatocellular obstruction and not extrahepatic obstruction
- Urine bilirubin and urobilinogen are important in differential diagnosis of jaundice
Determination of Alanine and Aspartate Transaminase Activity in Serum (AST & ALT)
- AST and ALT are enzymes present in specific tissues, catalyzing reversible transfer of α-amino group from amino acid to α-keto acid
- They are present in almost all cells, but higher amounts occur mainly in the liver, brain, heart, and kidney
- Clinical significance:
- Measurement of AST and ALT enzymes is a useful indicator of liver function
- High concentration in the liver and kidney, with trace amounts in other tissues
Estimation of Alkaline Phosphatase Activity in Serum
- ALP is mainly derived from the liver and bone in adults, with small amounts from the intestinal component
- During childhood, the majority of alkaline phosphatase is of skeletal origin
- During pregnancy, ALP is also contributed from the placenta
- ALP is activated by magnesium ions
- Clinical significance:
- Measurement of ALP activity is a useful indicator of liver and bone function
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Description
This quiz covers the clinical significance of uric acid levels in serum and urine, including factors that affect uric acid levels and diseases associated with increased uric acid levels.
