Uric Acid Concentration in Serum and Urine

Study Notes

Uric acid levels are affected by exercise and diet containing purine
Normal uric acid excretion occurs through urine, and increased levels in blood are accompanied by increased excretion in urine
Elevated uric acid levels are seen in several diseases, including:
- Renal failure
- Leukemia
- Multiple myeloma
- Lymphoma
- Glycogenesis
- Chronic hemolytic anemia
- Pernicious anemia
- Lymphosarcoma
Specifically, uric acid levels can increase up to 6.5-12 mg/dl in gout, 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
50% of total plasma calcium exists in ionized form, which is functionally most active
Calcium binds to negatively charged sites on proteins in a pH-dependent manner
Alkaline conditions promote calcium binding and decrease free calcium, whereas acidic conditions decrease calcium binding and increase free calcium levels
Clinical significance:
- Calcium levels are increased in hyperparathyroidism
- Hypocalcemia is a more serious and life-threatening condition than hypercalcemia
- In rickets, the product of serum calcium and phosphorus decreases, usually below 30 mg/dl
- An increase in alkaline phosphatase activity is a characteristic feature of rickets

Phosphorus has two forms: organic and inorganic
Inorganic phosphorus is present in the blood as phosphates of alkaline and alkali earth metals (H2PO4 and HPO4-2)
The ratio of H2PO4 and HPO4-2 is pH-dependent
Organic phosphorus includes glycerophosphates, nucleotide phosphate, and hexose phosphate

Bilirubin metabolism involves the conversion of heme to bilirubin in reticuloendothelial cells
Unconjugated bilirubin is transported to the liver, where it is conjugated with glucuronic acid to form conjugated bilirubin
Conjugated bilirubin is water-soluble and excreted through the bile
Clinical significance:
- In hemolytic jaundice, unconjugated bilirubin is increased due to increased destruction of red blood cells
- In hepatic jaundice, conjugated bilirubin decreases along with decreased excretion of bilirubin
- In posthepatic jaundice, the concentration of conjugated bilirubin is increased compared to unconjugated bilirubin
- Total serum bilirubin amount >40 mg/dl indicates hepatocellular obstruction and not extrahepatic obstruction
- Urine bilirubin and urobilinogen are important in differential diagnosis of jaundice

These enzymes catalyze the reversible transfer of the α-amino group from amino acids to α-keto acids
They are present in almost all cells, but higher amounts occur mainly in the liver, brain, heart, and kidney
Two clinically important transaminases are:
- Glutamine oxaloacetate transaminase (SGOT), also called aspartate aminotransferase (AST)
- Glutamine pyruvate transaminase (SGPT), also called alanine aminotransferase (ALT)
The measurement of these enzymes is a useful diagnosis indicator of liver functions

ALP of normal serum in adults is mainly derived from the liver and bone, 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:
- Elevated ALP levels are seen in various diseases, including bone diseases and liver diseases