Blood composition depends on three major factors:
Diet, cellular metabolism, and urinary output.
How much blood plasma is filtered from the kidney's 2 million nephrons in 24 hours?
150 to 180 liters.
How much urine is produced in 24 hours?
1.0 to 1.8 liters.
Color of urine
Freshly voided urine is generally clear and pale yellow to amber in color. This normal yellow color is due to urochrome, a pigment metabolite arising from the body's destruction of hemoglobin (via bilirubin or bile pigments). As a rule, color variations from pale yellow to deeper amber indicate the relative concentration of solutes to water in the urine. The greater the solute concentration, the deeper the color. Abnormal urine color may be due to certain foods, such as beets, various drugs, bile, or blood.
Odor of urine
The odor of freshly voided urine is slightly aromatic, but bacterial action gives it an ammonia-like odor when left standing. Some drugs, vegetables (such as asparagus), and various disease processes (such as diabetes mellitus) alter the characteristic odor of urine. For example, the urine of a person with uncontrolled diabetes mellitus (and elevated levels of ketones) smells fruity or acetone-like.
pH of urine
Ranges from 4.5-8.0, but its average value, 6.0, is slightly acidic. Diet may markedly influence the pH of urine. For example, a diet high in protein (meat, eggs, cheese) and whole wheat products increases the acidity of urine. Such foods are called acid ash foods. On the other hand, a vegetarian diet (alkaline ash diet) increases the alkalinity of the urine. A bacterial infection of the urinary tract may also result in urine with a high pH.
Specific gravity of urine
Specific gravity is the weight of a specific volume of liquid when compared with an equal volume of distilled water. SG of water is 1.000, because 1 ml weighs 1 g. Since urine contains dissolved solutes, it weighs more than water, and its customary specific gravity ranges from 1.001 to 1.030. Urine with a specific gravity of 1.001 contains few solutes and is considered very dilute. Dilute urine commonly results when a person drinks excessive amounts of water, uses diuretics, or suffers from diabetes insipidus or chronic renal failure. Conditions that produce urine with a high specific gravity include limited fluid intake, fever, and kidney inflammation, called pyelonephritis.
Kidney stones. If urine becomes excessively concentrated, some of the substances normally held in solution begin to precipitate or crystallize, forming these.
Normal constituents of urine (in order of decreasing concentration)
Water, urea, sodium, potassium, phosphate, and sulfate ions; creatinine; and uric acid. Much smaller but highly variable amounts of calcium, magnesium, and bicarbonate ions are also found in urine. Abnormally high concentrations of any of these urinary constituents may indicate a pathological condition.
Condition in which glucose is present in the urine. Indicates abnormally high blood sugar levels. Normally, blood sugar levels are maintained between 80 and 100 mg/100 ml of blood. At this level, all glucose in the filtrate is reabsorbed by the tubular cells and returned to the blood. Glycosuria may result from carbohydrate intake so excessive that normal physiological and hormonal mechanisms cannot clear it from the blood quickly enough. In such cases, the active transport reabsorption mechanisms of the renal tubules for glucose are exceeded-- but only temporary.
Occurs in conditions such as uncontrolled diabetes mellitus, in which the body cells are unable to absorb glucose from the blood because the pancreatic islet cells produce inadequate amounts of insulin, or there is some abnormality of the insulin receptors. Under such circumstances, the body cells increase their metabolism of fats, and the excess and unusable glucose spills out in the urine.
Condition in which albumin is present in the urine. Abnormal. Albumin is the single most abundant blood protein and is very important in maintaining the osmotic pressure of the blood. Albumin, like other blood proteins, is too large to pass through the glomerular filtration membrane. Thus, albuminuria is generally indicative of abnormally increased permeability of the glomerular membrane. Certain nonpathological conditions, such as excessive exertion, pregnancy, or overabundant protein intake, can temporarily increase the membrane permeability, leading to physiological albuminuria. Pathological conditions resulting in albuminuria include events that damage the glomerular membrane, such as kidney trauma due to blows, the ingestion of poisons or heavy metals, bacterial toxins, glomerulonephritis, and hypertension.
Condition in which excessive amounts of ketone bodies are present in the urine. Ketone bodies (acetoacetic acid, beta-hydroxybutyric acid and acetone) normally appear in the urine in very small amounts. Usually indicates that abnormal metabolic processes are occurring. The result may be acidosis and its complications. Ketonuria is an expected finding during starvation, or diets very low in carbohydrates, when inadequate food intake forces the body to use its fat stores. Ketonuria coupled with a finding of glycosuria is generally diagnostic for diabetes mellitus.
The appearance of red blood cells, or erythrocytes in the urine. Almost always indicates pathology of the urinary tract, because erythrocytes are too large to pass through the glomerular pores. Possible causes include irritation of the urinary tract organs by calculi (kidney stones), which produces frank bleeding; infection or tumors of the urinary tract; or physical trauma to the urinary organs. In healthy menstruating females, it may reflect accidental contamination of the urine sample with the menstrual flow.
The presence of hemoglobin in the urine. A result of the fragmentation, or hemolysis, of red blood cells. As a result, hemoglobin is liberated into the plasma and subsequently appears in the kidney filtrate. Hemoglobinuria indicates various pathological conditions including hemolytic anemias, transfusion reactions, burns, poisonous snake bites, or renal disease.
Nitrites in the urine
The presence of urinary nitrites might indicate a bacterial infection, particularly E. coli or other gram-negative rods. Nitrites are valuable for early detection of bladder infections.
The appearance of bilirubin (bile pigments) in urine. An abnormal finding and usually indicates liver pathology, such as hepatitis, cirrhosis, or bile duct blockage. Bilirubinuria is signaled by a yellow foam that forms when the urine sample is shaken. Urobilinogen is produced in the intestine from bilirubin and gives feces a brown color. Some urobilinogen is reabsorbed into the blood and either excreted back into the intestine by the liver or excreted by the kidneys in the urine. Complete absence of urobilinogen may indicate renal disease or obstruction of bile flow in the liver. Increased levels may indicate hepatitis A, cirrhosis, or biliary disease.
The presence of white blood cells or other pus constituents in the urine. It indicates inflammation of the urinary tract.
Hard-ended cell fragments, usually cylindrical, which are formed in the DCT and collecting ducts and then flushed out the urinary tract. Hyaline casts are formed from a mucoprotein secreted by tubule cells. These casts form when the filtrate flow rate is slow, the pH is low, or the salt concentration is high, all conditions which cause protein to denature. RBC casts are typical in glomerulonephritis, as RBCs leak through the filtration membrane and stick together in the tubules. WBC casts form when the kidney is inflamed, which is typically a result of pyelonephritis but sometimes occurs with glomerulonephritis. Degenerated renal tubule cells form granular or waxy casts. Broad waxy casts may indicate end-stage renal disease.
Chemical substances that form crystals or precipitate from solution; for example, calcium oxalates, carbonates, and phosphates; uric acid; ammonium ureates; and cholesterol. Also, if one has been taking antibiotics or certain drugs such as sulfa drugs, these may be detectable in the urine in crystalline form. Normal urine contains very small amounts of crystals, but conditions such as urinary retention or UTI may cause the appearance of much larger amounts (and their possible consolidation into calculi). These tend to be more minute than the organized (cellular) sediments.
Include epithelial cells (rarely of any pathological significance), pus cells (WBCs), RBCs, and casts. Urine is normally negative for organized sediments, and the presence of the last three categories mentioned, other than trace amounts, always indicates kidney pathology.