Carbon Dioxide or Bicarbonate

Acid-base disturbances are often recognized by abnormalities in the carbon dioxide (CO2) content of blood, which is composed primarily of bicarbonate (HCO3-), with small amounts of carbonic acid and dissolved carbon dioxide. The reference range for CO2 is 22 to 29 mmol/L. A reduced serum bicarbonate concentration frequently suggests metabolic acidosis, particularly when combined with a low pH. An elevated serum bicarbonate level frequently occurs with metabolic alkalosis. Bicarbonate is often used as a buffer for excess acid production, and levels are reduced in metabolic acidosis. In the evaluation of acidosis, calculation of the serum anion gap is helpful in determining the cause of the acidosis, as follows:

The normal range is 10 to 12 mmol/L. An increased anion gap generally indicates the presence of metabolic acidosis with elevation of unmeasured ions, such as lactic acid, phosphates, sulfates, and ketoacids. A normal anion gap acido-sis is seen with bicarbonate losses and increased chloride resorption and most frequently occurs with chronic diarrhea, but also with certain types of renal tubular acidosis. Low anion gaps can occur with hypoalbuminuria, congestive heart failure, and occasionally, multiple myeloma.

An elevated serum bicarbonate level frequently occurs in the setting of metabolic alkalosis. Metabolic alkalosis can be generated by loss of acid, such as in vomiting, but normally the kidney corrects the abnormality promptly by excreting excess bicarbonate. To maintain a metabolic alkalosis, the kidney must not be able to excrete excess bicarbonate. This

Table 15-14 Common Causes of Leukocytosis or Leukopenia Stratified by White Blood Cell (WBC, Leukocyte)Type

Condition

Description

Leukocytosis

Neutrophilia

Infections, leukemia, rheumatic and autoimmune disorders, neoplastic disorders, chemicals, trauma, endocrine and metabolic disorders, hematologic disorders, drugs

Eosinophilia

Infectious diseases, parasitic infections, allergic diseases, myeloproliferative and neoplastic diseases, cutaneous diseases, gastrointestinal diseases

Basophilia

Allergic reactions, chronic myeloid leukemia, myeloid metaplasia, polycythemia vera, ionizing radiation, hypothyroidism, chronic hemolytic anemia, splenectomy

Monocytosis

Infections, neoplastic disorders, gastrointestinal disorders, sarcoidosis, drug reactions, recovering from marrow suppression

Lymphocytosis

Viral infections, lymphocytic leukemia, other infectious diseases, neoplastic disorders

Leukopenia

Neutropenia

Overwhelming bacterial infection, viral infection, drug reaction, ionizing radiation, hematopoietic diseases, hypersplenism, anaphylactic shock, cachexia, autoimmune disease

Eosinopenia

Acute stress (usually physical), acute inflammatory states, Cushing's syndrome, corticosteroids

Basopenia

Sustained treatment with glucocorticoids, acute infection or stress, hyperthyroidism

Monocytopenia

Onset of steroid therapy; hairy cell leukemia

Lymphocytopenia

Immunodeficiency disorders, adrenocortical hormone excess, chemotherapeutic drugs, irradiation, impaired drainage of intestinal lymphatics, advanced lymphomas and carcinomas

From Speicher CE. The Right Test, 3rd ed. Philadelphia, Saunders, 1998.

abnormality usually occurs in the setting of volume depletion, when sodium reabsorption is enhanced and the sodium must be accompanied by an anion to maintain electroneu-trality. In the absence of available chloride in the urine, bicarbonate is reabsorbed with sodium, thereby maintaining the alkalosis. As mentioned earlier, urine chloride levels can assist in determining the cause of the metabolic alkalosis.

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