Interpreting Lab Results: A Primer

Interpreting Lab Results: A Primer

Tracy Call-Schmidt

Nurses encounter laboratory studies daily. Not only must they be able to understand the rationale for testing, but they must be able to evaluate results and modify care accordingly. Thus, reviewing the interpretation of the most commonly ordered laboratory tests is useful for developing and maintaining clinical competence. Tests such as complete blood count (CBC), potassium (K+), sodium (Na+), blood urea nitrogen (BUN), and creatinine levels (Cr) are among the most frequently ordered studies. In this overview, these tests and their interpretation, as well as nursing interventions that will help patients adapt to changes and reach homoeostasis, are described. Case studies will demonstrate clinical rationale and application, which will underscore how laboratory data should be used to monitor patients and intervene appropriately.

Serum Sodium

Sodium is the most abundant electrolyte in the extracellular fluid and plays an important part in fluid balance (Chernecky, 1993). The kidneys either conserve or excrete sodium, depending on the body’s needs. Serum sodium (Na+) measures the amount of Na+ present in the blood. Na+ levels will increase when there is a large loss of water without a loss of Na+ (for example, dehydration and diabetes insipidus). Na+ levels will also increase when there is an excessive intake of Na+ (for example, salty food intake and intravenous sodium chloride administration). In addition, vomiting can cause an increase in Na+ levels but a depletion of water (Corbett, 1992; Kee, 1994). Elevated sodium is known as hypernatremia.

Na+ levels will rise when both water and electrolytes are lost (for example, vomiting, diarrhea, and excessive nasogastric suctioning). On the other hand, Na+ may be depleted or decreased when the body is over-hydrated, and serum Na+ is diluted. Na+ may be decreased when the kidneys excrete Na+ excessively (for example, ketoacidosis or renal failure). A decreased sodium level is called hyponatremia. Normal values are presented in Table 1 (Chernecky, 1993; Corbett, 1992; Kee, 1994).

Table 1.

Normal Laboratory Values

Test Normal Range

Serum sodium (Na) 135-145 mEq/L

Potassium (K) 3.5-5.0 mEq/L

White blood cells (WBC) 4.5-11 x 10 UL

Creatinine (CR) 0.7-1.3 mg/dL Male

0.6-1.1 mg/dL Female

0.3-1.0 mg/dL Newborn

Blood urea nitrogen (BUN) 5-20 mg/dL Adult

4-6 mg/dL Infant

Tammy Snick, a 22-year-old female, presents to the floor after being admitted for observation overnight. She has had vomiting and diarrhea for the last 2 days and has been unable to keep anything down. She has also had a fever of 101.8 F for the last 2 hours. For the past 2 days she has been taking antipyretics to decrease her fever. Tammy seems anxious and is complaining of muscle twitches and a headache that “won’t go away.” Her blood pressure is 92/50 mmHg and her radial pulse is thready and quick (102 beats per minute). You notice her skin turgor is decreased and her skin feels cool and clammy. Dr. Job orders a sodium level. The resulting value is 129 milliequivalent per liter (mEq/L). Tammy is diagnosed with hyponatremia, which was caused by her vomiting and diarrhea which depleted her body of water and essential electrolytes.

In this scenario, several nursing interventions are considered. When a patient has hyponatremia (Na deficiency), input and output (I & O) should be monitored carefully (Leahy & Kizilay, 1998). Fluid excess can be a serious problem. Watch for evidence of edema, weight gain, and increased urinary output. These patients may need Na replacement and fluid restrictions. Sodium must be replaced slowly because if replaced in large doses it can cause circulatory overload (Ignatavicius, 1995). Certain medications, such as diuretics, can cause sodium to be depleted. Nurses must keep this in mind when they are reviewing patients’ medication regimen.

When a patient’s lab values show hypernatremia (Na excess), there are nursing interventions that are helpful in preventing future problems. Assess the patient for signs and symptoms of thirst, decreased urinary output, elevated temperature, and dry mucous membranes (Swearingen, 1994). These signs and symptoms indicate possible dehydration. Daily weights and strict monitoring of (I & O) recordings can help assess dehydration. In addition, devices such as central venous pressure monitors or wedges on a Swanz-Ganz catheter can be used to more accurately help assess fluid status (Baldwin, 1995). If the patient is hypernatremic, fluid replacement or Na restriction may be ordered. The patient’s fluid status is assessed carefully to watch for and prevent over hydration.

Central devices provide more accurate means to monitor fluid status. Central venous pressure (CVP) is a measurement which reflects blood pressure in the vena cava and the right atrium. It provides the nurse with information regarding blood volume and right ventricular end-diastolic pressure and function (Hudak, Gallo, & Morton, 1997). The CVP monitor can be attached to a machine to create a wave form for hemodynamic monitoring. CVP is measured in centimeters of water pressure. Normal values range between 5 cm to 8 cm (Hudak et al., 1997).

A pulmonary artery pressure monitor (PA), or Swan-Ganz, is used to monitor and assess right ventriclar function and cardiac output. The results obtained using a PA monitor assist in the diagnosis of cardiac and pulmonary dysfunctions (Hudak et al., 1997). The CVP and PA catheter are usually used in intensive care settings.

Serum Potassium

Serum potassium (K+) measures the amount Of potassium present in the blood. K+ is the most abundant electrolyte in intracellular fluid and plays an essential role in monitoring normal cardiac and neuromuscular functioning (Ignatavicius, 1995). It is also responsible for equilibrating the body’s proper acid/base balance. Hyperkalemia is the condition that results when potassium becomes elevated and can occur due to many causes. These include increased oral intake, intravenous infusion, or medications. Inadequate urinary output, such as seen in renal failure, can cause K+ levels to rise. Medications, such as diuretics, or metabolic changes, such as acidosis, elevate K+ levels in the body (Swearingen, 1994; Tierney, McPhee, & Papadakis, 1997).

When the body has a deficiency of potassium, hypokalemia occurs. This can be due to decreased intake of potassium or an excessive loss of potassium from the gastrointestinal tract, as seen in vomiting. In addition, medication, such as corticoid steroids, can deplete potassium. Hyperkalemia is seen with metabolic alkalosis when hydrogen is shifted out of the cell in exchange for potassium which enters the cell (Corbett, 1992). Normal potassium levels are presented in Table 1 (Chernecky, 1993; Corbett, 1992; Kee, 1994).

The relationship between Na+ and K+ is reciprocal. When serum Na+ falls, as with acute renal failure, serum K+ rises. When serum K+ falls, as with vomiting, serum Na+ rises (Baldwin, 1995; Kee, 1994).

John Holby, a 52-year-old male, is 2 days postcardiac surgery. While performing morning assessment the nurse compares John’s blood pressure of 110/80 with his usual blood pressure is 142/90. He states that he is feeling dizzy and sick to his stomach this morning and does not wish to have breakfast. He seems more irritable and fatigued than usual. Last night he was given 40 milligrams of furosemide (Lasix[R]) and voided 1 liter of urine. John’s ST segment is depressed compared to yesterday. The physician is notified of these changes, and a stat serum potassium (K+) level is ordered; the patient is monitored closely. John’s serum K+ is 3.0 mEq/L, and he is diagnosed with hypokalemia. This was attributed to the liter of fluid that was lost through diuresis. John’s signs and symptoms, such as hypotension, EKG changes, and nausea alerted the nurse to changes in potassium levels.

When K+ levels are low (hypokalemia), patients’ EKG rhythm should be monitored carefully. This is especially important for patients who are on digoxin, because digoxin can become toxic in the presence of low serum K+ (Tierney et al., 1997). Signs and symptoms of hypokalemia, such as muscle weakness, respiratory problems, and decreased abdominal bowel sounds, should be assessed and reported promptly (Corbett, 1992). When giving potassium IV, the solution must be diluted because concentrated K+ can damage veins (Wieland & Ciranowicz, 1995). Urinary output should also be checked every 1 to hours or as ordered by the physician or hospital protocol. Standing protocols for when to check K+ and its replacement when low are common. Nurses should familiarize themselves with unit and institutional policies.

Several nursing interventions are indicated when changes in potassium levels are dangerous for patients (Swearingen, 1994). Nurses must report signs and symptoms of potassium level alterations immediately. The patient with hyperkalemia may become irritable or restless and may complain of nausea, diarrhea, and cramping in the abdomen. As severity increases, the patient can have difficulty breathing and EKG changes resulting in paralysis and even death (Swearingen, 1994; Tierney et al., 1997).

Medications such as calcium gluconates, sodium bicarbonate, glucose, and insulin or a Kayexalate[R] enema can be used to decrease potassium levels (Corbett, 1992; Leahy & Kizilay, 1998). If K+ levels are dangerously high, the patient may need dialysis to rid the body of the excess K+ (Ignatavicius, 1995). Keep in mind that by administering these medications or dialysis, the patient is at risk for developing a hypokalemia. Whether potassium is high or low, dietary or supplemental teaching may be needed (Leahy & Kizilay, 1998). Consulting with a dietician can help nurses teach patients and their families about how to make good food choices that fit into their lifestyles.

Complete Blood Count

A complete blood count (CBC) is a valuable tool because of the vast amount of information it conveys. The components of a CBC and normal ranges are noted in Table 2 (Chernecky, 1993; Corbett, 1992; Kee, 1994). The red blood cell (RBC) count indicates how many RBCs are present in the blood at a given time (Chernecky, 1993). An excess of RBCs, called polycythemia, can be related to several factors, some of which are normal. Individuals who live in higher altitudes or undergo extensive physical training can have polycythemia. Polycythemia vera (primary polycythemia) is a condition of unknown etiology that causes the bone marrow to produce RBCs at an increased rate. Secondary polycythemia produces the same result but is thought to be caused by a secondary disease process such as COPD or CHF. RBCs can also be decreased due to factors such as anemia, cancers in which the bone marrow is suppressed, or a lack of production of erythropoietin (a hormone made by the kidney that stimulates RBC production) (Kee, 1994).

Table 2.

Normal Lab Values in a CBC

Hematocrit (Het)

40%-54% Male

38%-47% Female

Hemoglobin (Hbg)

13.5-18.0 g/dL Male

12-16 g/dL Female

Red Blood Cell Count (RBC)

4.6-6.2 x 106/UL Male

4.2-5.4 x 106/UL Female

Lee Turbin, a 52-year-old male, uses oxygen daily. He was admitted to the ICU because his blood oxygen saturation at Dr. Brown’s office was 82% on 2 liters of oxygen. His skin has a cyanotic tint, and his blood pressure is 182/110. Mr. Turbin’s fingernails have a clubbed appearance, and he has 3+ edema in his feet and ankles.

The nurse auscultates Mr. Turbin’s lungs, which are clear in all lobes. His breath sounds are decreased in the bases bilaterally. His respiratory rate is 18, and he seems to be in no apparent distress. His chest has a barrel-like shape. His heart sounds are regular but distant and no murmurs are heard on auscultation. A history of congestive heart failure (CHF) and chronic obstructive pulmonary disease (COPD) are reported. Dr. Brown orders a complete blood count along with a variety of other tests. His results are as follows: Hb 20g/dL, Hct 56%, and RBC 6.8/UL. Secondary polycythemia is diagnosed and attributed to COPD and CHF. Mr. Turbin’s body has compensated for hypoxemia by increasing RBC production (Cahill, 1996).

Several nursing interventions are warranted. An increase in RBC count results in an increased viscosity or thickening of blood which places the patient at high risk for venous thrombosis (Baldwin, 1995). An intervention that prevents this complication is adequate hydration (Leahy & Kizilay, 1998). Dehydration can be prevented by monitoring patients’ I & O and daily weight changes and intervening appropriately. When patients are kept NPO for surgery for an extended period of time, the risk of dehydration is increased (Swearingen, 1994).

Red Blood Cell Indices

Several different RBC indices are used in diagnosis on anemia. Erythrocyte levels differentiate the type of anemia experienced by patients. The mean corpuscular volume (MCV) describes average red blood cell size. The mean corpuscular hemoglobin (MCH) indicates the amount of hemoglobin present in each red blood cell. The mean corpuscular hemoglobin concentration (MCHC) indicates what portion of each red cell is occupied by hemoglobin. If the MCV is normal, cell size is considered normal or normocytic. This is seen when blood is lost from the body, as with a large hemorrhage, but there is no change in the cell size. If the MCV is decreased, the cell is classified as microcytic or small cell size which can be caused by a dietary deficiency of iron. If the MCV is elevated, the cell size is increased or macrocytic (large cell size). The MCH or MCHC determines the coloring of the cell. If these values are normal, the cell will be described as normochromic. If color is decreased, the cell is described as hypochromic, such as in iron deficiency anemia. If color is increased, the cell is described as hyperchromic. Hyperchromicity is very rare because cells can only hold a finite amount of hemoglobin (Kee, 1994). Table 3 lists normal red blood cell indices and the classes and types of anemias are depicted in Table 4 (Chernecky, 1993; Corbett, 1992; Kee, 1994).

Table 3.

Normal Values: Red Blood Cell Indices

Mean corpuscular volume (MCV) 80-96

Mean corpuscular hemoglobin (MCH) 27-31

Mean corpuscular hemoglobin concentration (MCHC) 32-36 g/dL

Table 4.

Classes and Types of Anemias


Blood loss or sickle cell


Iron deficiency anemia


Folic acid deficiency and

pernicious anemia

Hematocrit is defined as the percentage of blood cells within the blood plasma. Hemoglobin is defined as the amount of the heme protein in the blood (Chernecky, 1993). The hematocrit increases when the plasma volume in the body decreases (for example, burns), or if there is a rise in the RBCs (for example, with transfusions). A decrease in the hematocrit may be due to increased volume in the body (for example, excessive IV fluids) or a lack of RBCs (for example, with bone marrow suppression) (Swearingen, 1994). A common cause of lowered hematocrit is loss of blood. Hemoglobin can also be decreased because of blood loss, but many other diseases or physiological processes can cause this (for example, sickle cell anemia or pregnancy) (Corbett, 1992). Elevated hemoglobin is not a common finding and treatment is not essential.

Nursing interventions are used to restore patients’ blood values. In acute situations, the patient’s fluid status is assessed to check for dehydration or overhydration (Leahy & Kizilay, 1998). Checking for blood loss (such as occult blood in stool, weakness, or visible bleeding) and signs and symptoms of shock are a must. Signs and symptoms of shock include: hemorrhage, hypotension, olguria or anuria, confusion, irritability, restlessness, unconsciousness, tachycardia, and cool and clammy skin (Swearingen, 1994; Tierney et al., 1997). It is important to note that laboratory results can be misleading. If the patient is bleeding actively or being aggressively rehydrate Hct drawn an hour ago may reflect the Hct at the present time (Corbett, 1992; Kee, 1994).

If the Hct is chronically low the patient may be completely asymptomatic because of compensatory adjustments by organs and systems to chronic blood serum changes (Kee, 1994; Tierney et al., 1997). Some chronic low Hcts can be raised by assuring adequate protein in the diet. It is helpful to discuss this with the dietitian to help determine the best mode of action for the patient. Daily iron supplements may be ordered, but patients should be informed that the supplements can be constipating and can cause the feces to turn black in color (Leahy & Kizilay, 1998). Reviewing medication and instructions is a necessity. Patients should be informed that the absorption of iron is increased when taken on an empty stomach and/or with products, such as orange juice, containing vitamin C (Swearingen, 1994). In addition, patients should not take antacids, cholesterol-lowering drugs, or tetracycline at the same time as iron because these drugs bind iron and prevent its absorption in the gut (Kee, 1994; Tierney et al., 1997). Iron supplements are usually taken for 3 months to restore blood levels and then continued for a total of 6 months to assure levels stabilize. When the hematocrit drops, patients may experience respiratory troubles unrelieved by oxygen administration (Kee, 1994; Swearingen, 1994). These patients may require blood replacement to restore their oxygen carrying capacity. Patients should be monitored for dyspnea or respiratory problems, which should be reported promptly to the physician. Patients with a low hematocrit may be more prone to infection as well (Ignatavicius, 1995). As always, universal precautions and good handwashing techniques are in order. Interventions related to hemoglobin will be discussed with erythrocyte indices.

Molly Zible, a 34-year-old female, presents to the emergency room complaining of dyspnea when climbing stairs or exerting herself. She reports feeling fatigued and irritable over the last 3 months, and she states that her symptoms seem to be getting worse. In addition, she tells you that she has been having frequent headaches, and she “just can’t concentrate anymore.” She reports that she has had the flu and four or five colds in the past year, when she usually is sick about once a year. Embarrassed, she tells you she has been craving laundry soap and dirt recently (known as pica). She states that she feels increasing pain when swallowing. She adds that she has been experiencing some numbness and tingling in her arms and legs.

On examination, cracks at the corners of the patient’s mouth are observed. Her nails look spoon-shaped and are somewhat thin and brittle. She is alert and oriented but is easily distracted. Her heart rate is 115 beats per minute, paralleling her quick, bounding pulse. Her skin is pale and her blood oxygen saturation is 90% on room air. The physician orders a CBC and the results are as follows: Hb 8 g/dL, Hct 34%, RBC 4.0 million/ML, MCV 78 g/dL, MCH 24 pg, and MCHC 30 g/dL. Molly is diagnosed with iron deficiency anemia. She is treated with iron supplementation.

There are numerous nursing interventions indicated for patients diagnosed with iron deficiency anemia. Dietary teaching and iron supplementation should be provided. Anemia related to acute blood loss may require blood replacement. If anemia is due to a chronic process, such as sickle cell anemia, teaching the patient about the disease process and learning how to cope with chronic disease is warranted. When the anemia is related to folic acid deficiency, teaching about replacements and consulting with the dietician to discover ways to increase intake of needed nutrients will result in improvement. Pernicious anemia requires teaching patients or their caregivers how to give B12 injections and supporting patients’ adjustment to the knowledge that these injections must be given for life (Corbett, 1992; Ignatavicius, 1995). Anemias and their respective interventions differ significantly. By diagnosing the specific anemia type through laboratory data interpretation, interventions and quality of care can be improved dramatically.

White Blood Cells

White blood count (WBC) is the number of white blood cells in a uniliter of blood (see Table 1) (Chernecky, 1993; Corbett, 1992; Kee, 1994). It includes monocytes, granulocytes, leukocytes, neutrophils, basophils, and eosinophils. A detailed discussion of differential WBCs is beyond the scope of this article. An elevated WBC count is usually indicative of an infectious process (Baldwin, 1995). Although sometimes it is difficult to pinpoint the cause, interventions to protect patients and return them to health are ideal. First, patients must be protected from acquiring other infections, either by Universal Precautions, good handwashing, or recommended isolation procedures. Since some allergies and medications cause WBCs to rise, a thorough medical history is necessary (Corbett, 1992; Kee, 1994). Anti-infectives may be prescribed and nurses should be familiar with these drugs and the side effects that they may cause.

BUN and Creatinine

Blood urea nitrogen (BUN) is used to determine the amount of urea nitrogen present in the blood at a given time (Kee, 1994). This test is an indicator of how well the kidneys are functioning. It is important to remember that factors such as protein intake and abnormal fluid balance (dehydration or over hydration) can cause an abnormal BUN (Chernecky, 1993; Swearingen, 1994). BUN may be increased for the following reasons: (a) when the kidneys are damaged because the kidneys are unable to rid the body of excess waste products, (b) increased oral intake of protein because urea is the end product when protein is digested, and (c) protein from digested blood, as in a GI bleed (Chernecky, 1993). Dehydration elevates BUN levels. Shock and CHF can elevate BUN as well by decreasing circulation to the kidneys causing a decreased urinary output (Baldwin, 1995; Kee, 1994). Over hydration and pregnancy also decrease BUN because of the increase in circulating plasma volume (Corbett, 1992; Kee, 1994).

Creatinine (CR) is used to determine kidney function (Chernecky, 1993). Unlike BUN, creatinine results are affected minimally by protein or hydration status (Corbett, 1992; Kee, 1994). Creatinine is another waste product given off by skeletal muscles that is excreted by the kidneys. When creatinine is elevated, it is usually related to direct destruction of kidney nephrons (Corbett, 1992; Kee, 1994). A decrease in creatinine may be seen when muscles atrophy, such as in prolonged bed rest with inactivity (Swearingen, 1994). Nursing interventions for elevated or decreased creatinine levels are similar to those for altered BUN levels.

Monty Tos was admitted yesterday with a diagnosis of acute pyelonephritis. He has some nausea and diarrhea, and he is asking for assistance to the bathroom. He looks pale and seems irritable, and on examination, his blood pressure is 100/60 (which is quite low for him). His respirations exceed 26 breaths per minute. He states he has only been able to urinate once in the last 24 hours, and he is starting to get concerned. Tests reveal a blood urea nitrogen level of 28 mg/dL and a creatinine level of 2.2 mg/dL. Monty is treated for acute renal failure.

Nursing interventions for abnormal BUN and creatinine levels are based on the etiology of the abnormal values (Kee, 1994; Swearingen, 1994). The patient’s hydration status is assessed and is adjusted as needed. Dietary protein may be restricted if renal function is decreased. As a patient’s BUN increases, the patient may complain of nausea, vomiting, or fatigue (Ignatavicius, 1995; Swearingen, 1994). Changes in the level of consciousness require frequent neurologic checks and such increased safety measures as a side rails and restraints per hospital protocol.

When the client’s activities and fluids are decreased, there is an increased risk of constipation. Nurses must monitor bowel movements and give laxatives as ordered when needed (Leahy & Kizilay, 1998). If the BUN is increasing due to renal failure, medication levels in the bloodstream can increase (Hudak et al., 1997; Kee, 1994). The treatment team may need to adjust medication. Patients may accordingly have increased psychologic needs. They may feel hopeless, especially if they have been diagnosed with kidney failure and are trying to adjust to a chronic disease. Nurses work to help patients develop new coping mechanisms, reinforce existing effective coping mechanisms, and improve self-esteem (Ignatavicius, 1995).

Laboratory interpretation skills are vitally important for nurses, who must constantly reinforce and expand their expertise. By becoming familiar with commonly ordered tests and the indications of resulting data, nurses can intervene more effectively. A brief overview of the commonly ordered lab tests and values was presented here. Case studies were used to demonstrate variations in blood levels and their clinical consequences. Nurses use their laboratory interpretation skills to help identify or prevent patient problems and intervene appropriately. Increasing their knowledge of these tests assists nurses to correlate data regarding a patient’s history and symptoms, and to plan interventions to protect health and improve wellness.

Patients and families can increase their knowledge of these tests to help improve their understanding of how illnesses are diagnosed. Further, this information underscores the important role of testing in care intervention and evaluation.

As sodium is excreted through the kidneys, potassium is retained.

Example: Diabetic ketoacidosis

As sodium is retained in the body, it causes potassium to be excreted.

Example: Vomiting


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Tracy Call-Schmidt, MS, RN, FNP-C, is a Clinical Instructor, University of Utah College of Nursing, Salt Lake City, UT.

COPYRIGHT 2001 Jannetti Publications, Inc.

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