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Bilirubin, a product of hemoglobin breakdown, is characterized by its yellow pigment. The presence of bilirubin in urine is always abnormal. It is important to note that unconjugated bilirubin cannot be excreted by the kidneys because it is bound to albumin and is not soluble in water. In the liver, bilirubin combines with glucuronic acid through the action of a glucuronyl transferase to form water soluble bilirubin diglucuronide. Under normal circumstances, conjugated bilirubin passes from the bile duct and then to the intestinal tract. Intestinal bacteria reduce conjugated bilirubin to urobilinogen. Approximately half of the urobilinogen is excreted in the feces; most of the other half is recirculated through the liver. A small amount of urobilinogen bypasses the liver and is excreted in the urine.

Bilirubin is formed as a result of the breakdown of hemoglobin from erythrocytes in the reticuloendothelial system. It becomes bound to albumin and transported through the blood to the liver. This free or unconjugated bilirubin is insoluble in water and cannot be filtered through the glomerulus of the kidney. In the liver, bilirubin becomes conjugated with glucuronic acid to form bilirubin diglucuronide. This conjugated bilirubin, which is also called direct bilirubin, is water soluble and is excreted by the liver through the bile duct and into the duodenum.

Many lipophilic substances, including fat-soluble vitamins, cholesterol, and triglycerides are essential for life. The body needs to be able to absorb and transport these substances. However, lipophilic substances are not water-soluble, and, since blood is aqueous, this presents a challenge. The body addresses this need by using 'carriers' which can bind or sequester lipophilic molecules to aqueous 'vehicles' and thus transport them through the aqueous environment of the blood. Small lipid-soluble hormone molecules like estrogen, testosterone or cortisone are carried through the blood by binding to carrier proteins. Cholesterol and triglycerides are carried through the body in small spherical particles which trap the lipophilic molecules in their centers. These particles have an outer shell that is polar on the surface so that the particles are soluble in the blood but they have a lipophilic core which can hold fat-soluble molecules.

Fibrin strands woven into the clot structure are cleaved into soluble fibrin fragments, and then removed by macrophages. The action of fibrinolysis also serves to restore blood flow into the area that had been sealed off, helping to promote further healing. Fibrinolysis is mediated by a proteolytic enzyme called plasmin. Plasminogen is the inactive precursor form of plasmin that is found in plasma. Plasmin takes on fibrinolytic properties after activation, digesting both fibrin and fibrinogen. Inhibitors act to control the process, serving as a check and balance system for fibrinolytic activities.

Leucine crystals indicate a problem with the metabolism of the amino acid leucine. These crystals are round to oval with radiating bands going from a center point out to the periphery, often referred to as a "wagon wheel." These crystals are soluble in hot alcohol and alkali.