Uric Acid Concentration in Serum and Urine

Study Notes

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

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

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.)

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

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

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