During a dehydrated state, there is less water in the body. The concentration of blood constituents increases. The laboratory tests may present a misleading picture of the individual’s nutritional status. There are three types of dehydration based on serum sodium:
•Hypertonic dehydration
•Isotonic dehydration
•Hypotonic dehydration
Hypertonic dehydration occurs when body water losses are greater than sodium losses. This can be due to reduced oral intake, excessive losses from sweating or prolonged high fever. The sodium concentration rises in the extracellular compartment, which draws water osmotically from the intracellular fluids. A summary of laboratory tests used to diagnose different types of dehydration follows on Table 4. Additional information about each laboratory test is in the next section of this text.
Isotonic dehydration occurs when the body loses equal amounts of sodium and water. Gastrointestinal disturbances causing extreme diarrhea and/or vomiting can trigger isotonic dehydration. This type of dehydration is often seen with food borne illness or severe bleeding. The serum sodium levels, serum osmolality and specific gravity levels are within normal ranges. These individuals are not thirsty and do not sense the need for more fluid. Both fluid and sodium are needed to rehydrate the patient. Refer to Table 4.
Hypotonic dehydration occurs when the body sodium loss exceeds water loss. This is sodium depletion or hyponatremia. It occurs in the patient who is taking diuretics, on sodium restricted diets, experiencing diarrhea or vomiting, has excessive sweating, a renal sodium-wasting syndrome or a combination of these contributors. There is typically a reduction in extracellular fluid volume. The laboratory tests indicate abnormally low serum sodium levels. Treatment includes giving water-electrolyte solutions to rehydrate the patient. Refer to Table 4.
Table 4. Screening for Dehydration
| Lab Test | Hypertonic | Isotonic | Hypotonic |
| Osmolality (S) | >Normal | WNL | < Normal |
| Sodium, (S) | > Normal | WNL | < Normal |
| Hemoglobin | > Normal | > Normal | > Normal |
| Hematocrit | > Normal | > Normal | > Normal |
| Albumin, (S) | > Normal | > Normal | > Normal |
| BUN | > Normal | > Normal | > Normal |
| Urine Specific Gravity | > Normal | > Normal | < Normal |
Key: WNL= within normal limits
Assessment FOR Overhydration
Overhydration occurs when there is an increase in the extracellular fluid volume. The fluid shifts from the extracellular compartment to the interstitial fluid compartment. This is called edema and is typically caused by one of these mechanisms:
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•Lymphatic obstruction (following surgery)
•Organ failure (kidney or liver)
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Overhydration is categorized by serum sodium concentration levels which reflect the composition of the fluids retained. Each type of overhydration presents different pathophysiologic effects. There are three types of overhydration:
•Isotonic overhydration
•Hypertonic overhydration
•Hypotonic overhydration
Overhydration or edema is commonly seen in patients with congestive heart failure, low blood pressure, renal insufficiency, liver failure (ascites) and physical inactivity. The fluid retention is usually a symptom of a bigger medical problem.
Edema is usually treated with loop diuretics. Overdose of loop diuretics can cause extracellular fluid depletion and a potassium deficiency. The success of loop diuretics is measured by a significant weight loss and a decrease in edema. Laboratory tests will change rapidly as edema diminishes. Typical lab values seen in edema are summarized in Table 5. Additional information about each laboratory test is in the next section of this text.
Table 5. Screening for Overhydration
| Lab Test | Hypotonic | Isotonic | Hypertonic |
| Osmolality (S) | < normal | WNL | > normal |
| Sodium, (S) | < normal | WNL | > normal |
| Albumin (S) | < normal | WNL or slightly low | < normal |
| H/H | < normal | WNL or slightly low | < normal |
| BUN | < normal | WNL or slightly low | < normal |
Key: WNL= within normal limits
Assessment of Protein Status
Assessment of protein status is essential for baseline assessment and to predict risk for malnutrition and skin failure. A patient’s protein status is a reflection of the body’s ability to synthesize dispensable amino acids (DAA) and to absorb and utilize indispensable amino acids (IDAA). As the protein status declines the patient is at higher risk for infection, delayed wound healing and new skin breakdown. The traditional method to estimate visceral protein status is using a variety of lab test results including retinol binding protein level, prealbumin (transthyretin) and serum albumin. However all of these measures are negative acute phase proteins and are dramatically affected by inflammatory processes. Changes in these values do not appear to reflect changes in nutritional status. For more information refer to Protein, Blood, for more information on retinol binding protein, prealbumin and albumin.
Nitrogen Balance Studies
Nitrogen balance studies reflect the balance between exogenous nitrogen intake (by mouth or parenteral) and renal removal of nitrogen containing compounds (urinary, fecal, wound and other nitrogen sources). Nitrogen balance studies are often part of research studies to determine if the endogenous protein is being utilized. However, in a healthcare setting, nitrogen balance studies are not a measure of protein anabolism and catabolism because true protein