II. Blood chemistry

A. Blood Urea Nitrogen (BUN)

The normal value is 9 to 19 mg per 100 ml.

Principle: Urea is the end product of protein metabolism. Titration is the preferred method for its determination.

Interpretation: These values are raised in severe renal disease and lower in pregnancy and malnutrition.

Comment: NPN tests which arrive at essentially the same information should be eliminated in lieu of the BUN test.

B. Total serum protein.

This is composed chiefly of albumins, globulins, and fibrinogens. The nornal level is 6 to 7.8 grams per 100 ml.

Indications: The determination of total proteins supplies only limited information except in conditions of shock and dehydration, where concentrations increase, or in hemorrhage, where the level tends to decrease.

Total serum protein levels are low in the presence of kidney disease, liver disease, malnutrition, and protein loss in hemorrhagic shock. They are high in cases of chronic infections, early liver disease, reticuloendothelial disease, and dehydration.

Comment: This test may be used as a guide in parenteral fluid administration in an emergency.

C. Serum glocose (Fasting blood sugar)

The normal value is 80 to 120 mg per 100 ml.

Principle: Titration or colorimetry may be used. This determination is primarily a test for diabetes, but it may also reveal other pathologic processes.

Serum glucose levels are increased in diabetes mellitus, acromegaly, adrenal tumors, anoxia (that is, in general anesthesia, tetany, and epilepsy), brain injuries, and chronic hepatic dysfunction. Serum glucose levels are decreased in disease of the islets of Langerhans, hypopituitarism, and hypothyroidism.

Comment: Presumptive diagnosis may be made with values above 120 mg, but to confirm this diagnosis a glucose tolerance test may be necessary.

D. Carbon dioxide (capacity of plasma)

The normal is 25 to 31 mM per liter or 55 to 70 volumes per cent.

Indications: This test is used in cases of acid base imbalance.

Low carbon dioxide (acidosis) is found in hyperventilation (fever, hysteria, etc), Addison's disease, diarrhea, intestinal fistula, and diabetic acidosis. High carbon dioxide (alkalosis) is found in pulmonary disease (from hypoventilation) and intestinal obstruction.

E. Serum chlorides

The normal is 570 to 620 mg per 100 ml (also expressed in milliquivalents).

Indication: This test should be performed when an electrolyte imbalance is suspected.

Serum chloride levels are raised in kidney disease, excessive IV saline, and dehydration and water loss. Lowered serum chloride levels are found in cases of vomiting and diarrhea and diabetic acidosis.

F. Serum Sodium and Potassium.

The normal value for potassium is 4.0 to 5.0 m.e. per liter, and the normal value for sodium is 138 to 145 m.e. per liter.

Principle: There are many methods, but flame photometry is the most accurate.

Interpretation: These tests are usually employed with the prolonged use of intravenous feedings or in the presence of any electrolyte imbalance.

Sodium deficiency is seen in cases of lowered intake, excessive perspiration, gastrointestinal discharge, kidney disease, and Addison's disease. Potassium deficiency occurs in cases of vomitting and diarrhea, diabetic acidosis, and overexcretion.

There is a sodium increase in overadministration of saline and in dehydration (more water loss than sodium loss). There is a potassium increase in excessive loss of chlorine as potassium chloride, heart failure and shock with tissue anoxia, adrenal cortical insufficiency, and excessive intake.

Comment: In general, it may be stated that values for serum potassium increase as values for sodium decrease.

G. Serum calcium.

The normal is 9 to 11.5 mg per 100 ml.

Indication: Serum calcium should be determined whenever osteoclastic activity is suspected.

Serum calcium levels are reduced in hypoparathyroidism, bone disease, and vitamin D deficiency. These levels are elevated in hyperparathyroidism and hypervitaminosis D.

H. Serum phosphorus.

The normal is 3 to 4.5 mg per 100 ml.

Indications: In general, the indications for determining the serum phosphorus level are the same as for testing serum calcium.

Serum phosphorus levels are increased in nephritis, bone fractures, hyperparathyroidsm, and osteoclastic bone metastasis and decreased in vitamin D deficiency.

Comment: This test is usually run in conjunction with the serum calcium test, as is the alkaline phosphatase.

I. Alkaline phosphatase.

Alkaline phosphatase is the enzyme that splits the phosphate group in alkaline media. The normal value for adults is 1.5 to 4 Bodansky or 1.3 to 3.5 phenol units.

High alkaline phosphatase levels are seen in the presence of any bone disease, osteoblastic activity, liver disease, Paget's disease, rickets, osteomyelitis, and hyperparathyroidism.

Comment: A lowered alkaline phosphatase has little or no significance.