Top 10 laboratory tests: blood will tell - includes related information - part 1

FDA Consumer, July-August, 1989 by Dixie Farley

Significance of results: Too much circulating potassium--hyperkalemia--is due most frequently to kidney disease that interferes with potassium excretion. Also, a deficiency in adrenocortical hormone can lead to hyperkalemia. Abnormally high potassium levels can result from a severe burn or crushing injury. In these cases, potassium is released from damaged cells more quickly than the kidneys can eliminate it; the shock that may accompany severe trauma compounds the problem by slowing kidney function. Twenty-four hours after such an injury, the situation is reversed as fluid enters the circulation to bring potassium levels down. Too much potassium can cause diarrhea, irritability, muscle cramps, and ultimately irregular heartbeat and death.

Too little potassium is called hypokalemia, which can lead to or result from alkalosis, an abnormal alkaline state. Among other causes of hypokalemia are prolonged intravenous feeding of a potassium-free solution, liver disease associated with alcoholism, and excessive potassium loss from chronic diarrhea or long-term use of diuretics. Severe depletion can lead to death. Symptoms of potassium loss include weak pulse, falling blood pressure, and weakness.

Chloride, a Team Player

Measurement: The amount of chloride in serum.

Normal range: 97 to 108 mEq/L.

Use: Problems develop less often with chloride than other electrolytes. Any that do show up usually are related to abnormal levels of other electrolytes. Hence, this test is used in conjunction with a test for another electrolyte.

Comments: The primary anion in the fluid outside cells, chloride teams with sodium (table salt is sodium chloride) to regulate fluid pressure across cell membranes.

Significance of results: Chloride levels decrease when the body has lost excessive fluid. This causes bicarbonate to increase to maintain the necessary anion level in serum, which, in turn, can lead to alkalosis. Symptoms of alkalosis include nervousness and numbness or tingling in the hands or feet.

Chloride is elevated in kidney inflammation, overactive thyroid, anemia, and heart disease.

Sodium and Fluid Balance

Measurement: The amount of sodium concentration in plasma.

Normal range: 136 to 145 mEq/L.

Use: Candidates for sodium testing include older people who may not drink enough water, people who may be dehydrated, patients taking certain drugs (lithium, for example), and patients who have experienced a rapid change in weight or mental status. People with a chronic illness such as kidney failure, congestive heart failure, or cirrhosis also may need periodic sodium testing. This test is not a measure of total body sodium, so it is not intended to show, by itself, whether a patient should alter sodium intake. Water retention can, in fact, cause a low plasma sodium level when the total body sodium actually is increased.

Comments: Sodium's major role is to maintain fluid balance. It accounts for 90 percent of the cations in fluid outside of cells. Sodium attracts water; hence, increased sodium concentration draws water out of cells, causing them to shrink and sometimes malfunction. To compensate, the adrenal gland secretes less of the hormone aldosterone, and that causes the kidneys to step up sodium excretion. When sodium concentration is low, the process is reversed: Elevated secretion of aldosterone causes the kidneys to reabsorb sodium, which leads to water retention.