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Interpreting common lab values.

This independent study has been developed to enhance the ability to interpret four common lab tests as well as blood gas findings. 1.05 contact hour will be awarded.

The Ohio Nurses Association (OBN-001-91) is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's Commission on Accreditation.

(Expires 1/2018).


1. Please read carefully the attached article entitled "Interpreting Common Lab Values," and answer the post-test questions.

2. Return the following to the Indiana State Nurses Association, 2915 N. High School Road, Indianapolis, IN 46224.

--The post-test;

--completed registration form;

--and evaluation form.

The post-test will be reviewed. If a score of 70 percent or better is achieved, a certificate will be sent to you.

If a score of 70 percent is not achieved, a certificate will not be issued. A letter of notification of the final score and a second posttest will be sent to you. We recommend that this independent study be reviewed prior to taking the second post-test. If a score of 70 percent is achieved on the second post-test, a certificate will be issued.

If you have any questions, please feel free to call Marla Holbrook at 317-299-4575 or

The author of this study is Barbara Walton, MS, RN. The author and planning committee members have declared no conflict of interest.

Outcome: Enhance the ability to interpret four common lab tests as well as blood gas finding.

Disclaimer: Information in this study is intended for educational purposes only. It is not intended to provide legal and/or medical advice.

DIRECTIONS: Read the following case studies. Answer the questions regarding each case study and then review the correct answer and its explanation. At the end of the program, complete the post-test by circling the one correct answer for each multiple-choice question.


Mrs. J. has brought her 4 year old son, Todd, to the office with complaints of persistent nose bleeds. She states he has a nose bleed at least once a day and she has noticed that he seems to have more bruises on his arms than usual. Your physical exam reveals several ecchymotic areas on both arms in various stages of healing. He denies any trauma to the areas, stating that they "just happen." His last nose bleed was yesterday around noon. He denies nose picking or other trauma. He states, in fact, that he was just "watching TV" when his nose began to bleed yesterday. His mother states the bleeding is always profuse, usually from both sides of the nose and it generally takes about 15 minutes to get it stopped. His vital signs are: T 98.6, B/P 80/60, HR 100, R 22. Ht 42 inches, and wt 45 lbs.

1. In light of your findings and the patient's history, what blood studies would you expect the physician or APN to order?


If you answered CBC with diff, PT, PTT, and platelets you are right on target! Let's take a look at why these tests would be ordered.

By definition, epistaxis is bleeding from the nose caused by irritation, trauma, coagulation disorders, or chronic infection. The history obtained from the patient and his mother rules out trauma and irritation, leaving coagulation disorder and infection as strong possibilities. He also has several bruises which may hint at some hematologic problem. His lab results are:


RBC         4.0 million
MCV         80
MCH         27
Hgb         9.4
Hct         31%
Platelets   80,000
WBC         75,000


Neutrophils   65%
Lymphocytes   32%
Monocytes     3%
Eosinophils   3%
Basophils     .5%

2. Identify which of the above lab values are normal or abnormal by placing an N or an A next to each result.


Let us now review your answers about whether or not these are normal lab values.

RBC: 4.0 million

This is a low normal value for a child 4 years of age. Normal value is 4.5-5.2 million, although values for all lab findings may vary slightly from lab to lab.

MCV: 80

The mean corpuscular volume of the red blood cell determines the size and volume of each red blood cell. The normal for this patient would be 80. If you marked it normal you were right!

MCH: 27

This is the mean corpuscular hemoglobin and determines the hemoglobin content in RBCs. (Hemoglobin of 100 ml of RBCs). Todd's value is normal.

These corpuscular tests are helpful when diagnosing certain types of anemias, hepatic disease, iron deficiency, malaria and many other disorders that affect the hematologic system.

Hgb: 9.4

This determines the amount of hemoglobin in a given volume of blood. A four year old child should run between 9.4 and 15.5. Todd is on the low side of normal.

Hct: 31%

The hematocrit determines the percentage of blood composed of RBCs. Todd should fall between 31% and 44%. Again, our patient is on the low end of normal.

Platelets: 80,000

The platelet count determines the number of platelets in 1 mm3 of blood. Normal platelet count would be about 250,000. Did you mark this test result as abnormal? Since platelets play a significant role in coagulation, this may be part of the reason for Todd's bruises and his frequent epistaxis.

WBC: 75,000

The WBC gives us the number of white blood cells in 1 mm3 of blood. Normal for Todd should be 5700-13,000. His WBC is extremely elevated, more than would be expected if he just had an infection. Our next step is to look at the differential to see if it will tell us more about Todd's problem.

Neutrophils: 65%

In a WBC differential, 100 or more white cells are classified into two major types of leukocytes: granulocytes (neutrophils, eosinophils, basophils) and nongranulocytes (lymphocytes and monocytes). Neutrophils play an important role in fighting bacterial infection in the body. Large numbers of neutrophils can be produced by the bone marrow in response to infection. Soon, however, our body runs out of mature neutrophils and begins pushing immature ones into our system. Immature neutrophils (called blasts, bands or stabs) are not as effective as mature neutrophils. An increase in the immature neutrophils is called a "shift to the left." Normal neutrophil count for Todd would be about 5060. His is elevated, indicating either a ferocious infection or a problem with the white cells themselves.

Eosinophils: 3%

Eosinophils elevate in times of allergic reaction. Normal is 1-3% of the WBC. Todd is normal here.

Basophils: .5%

Basophils work in hypersensitivity reactions and enhance the inflammatory response. Normal value is 0-0.75%. Todd falls within normal limits.

Lymphocytes: 32%

Usually about 30% of the total white blood cell count is lymphocytes. They play a major role in cell-mediated and humoral immunity and are divided into T-cell and B-cells. This is an abnormal elevation for Todd.

Now let us put all this information together. Todd has a grossly elevated WBC with a pronounced "shift to the left." The lymphocyte count stands out as well. His platelet count is decreased and his H/H is borderline low. All of this data may indicate that Todd is experiencing acute leukemia and that is the reason for his frequent epistaxis and many bruises. However, further testing would be indicated, especially a blood smear which would show numerous blast (immature) cells. A bone marrow biopsy might also be scheduled and would also reveal massive blast cells.


Ms. S. is a 24 year old female who presents to the office with complaints of severe diarrhea. She states she has been having at least ten bowel movements per day. She describes them as watery brown, somewhat mucousy and in large amounts. She also states she has severe cramping with them. She claims she has never experienced this in the past. Your physical examination reveals a very thin, pale woman with dry mucus membranes and poor skin turgor. She is 5'7" tall and weighs 105 pounds. She states this is ten pounds below her usual weight.

She is on no medications and states she thought she just had the "flu" but became concerned when it did not clear up in a few days.

Vital signs are T 99, HR 100, RR 24, B/P 90/60 in the upright position.

1. Given this information, what blood chemistries would you expect to be ordered?


Most of you would agree that the physician or APN would probably order at least serum electrolytes, BUN and creatinine in addition to a stool culture.

Ms. S's blood chemistries were:

Na    130
Cl    92
K     3.0
CO2   22
Cr    1.0
BUN   20

2. Take a moment now to write N for normal or A for abnormal next to each of the values.

Let us now take a look at each value and see what information it gives us.

Na: 130

If you labeled this as abnormal, you are right. Normal serum sodium for adults is about 135145. Again, it is important for you to familiarize yourself with the values used at your lab since they may vary slightly from lab to lab.

Cl: 92

This is abnormally low. The normal range is 97-107.

CO2: 22

This falls within the normal limits of 22-30.

Cr: 1.0

A normal creatinine is .5-1.1.

BUN: 20

This is an elevated level since the normal is about 5-18.

You probably had no problem recognizing the abnormal values with this patient. Now let us put all the values together so that we can draw some conclusions about Ms. S's problem.

Your examination of the patient revealed signs of dehydration. She has dry mucus membranes and poor skin turgor. Her heart rate is 100 and her B/P 90/60. She also has a recent weight loss of ten pounds. As we look at the lab values to validate our assessment we see that she has a low Na and Cl level and an elevated BUN. These can be indicators of dehydration.

There are several subgroups of water-sodium imbalances: osmolar imbalances, which have to do with the amount of water in the body in relation to the number of solutes, and volume imbalances, in which sodium, chloride and water work together as a team. This patient has a typical hypovolemia characterized by loss of Na, Cl, and water together. The BUN also reveals some information. An elevated BUN unaccompanied by an elevation in the creatinine can often be found when patients are hypovolemic or in a starvation state where protein begins to be catabolized (broken down) for energy. Our patient fits this picture as well.

A low serum potassium can be accounted for by the large volumes of diarrhea. Classically, diarrhea causes at least three major fluid and electrolyte imbalances: dehydration, NA deficit, and K deficit. The body has compensatory mechanisms such as fluid shifts, aldosterone and ADH secretion which attempt to deal with the fluid and electrolyte disturbances caused by diarrhea. In this patient's case, these mechanisms were not enough to correct her problems.

Our initial lab values show dehydration, hyponatremia, hypochloremia, and hypokalemia. These are the results of the patient's problem but do not give us the full picture. More information is needed to further identify the cause of her diarrhea. She may be suffering from her first episode of ulcerative colitis. In the meantime, you could expect the physician or APN to treat the fluid and electrolyte disturbances because further depletion could result in severe complications such as cardiac dysrhythmias and renal failure.


Mr. M. is a 59 year old male who has been under the care of your physician group for several years. He has a long history of emphysema, having been a 50 pack/yr smoker. During the last year he has been hospitalized twice for respiratory failure, the last time resulting in a two week stay in the intensive care unit on a ventilator. For the last two months, Mr. M. has been relatively well. He has presented himself to the office for a routine check-up. He is 5'9" and weighs 180 pounds. Vital signs are T 98, HR 100, RR 38, B/P 150/90. He denies shortness of breath but appears to be working hard at his breathing, using all of his accessory muscles. His lips and nailbeds are slightly cyanotic. The physician orders a set of arterial blood gases. You accompany Mr. M. to the lab next door and await the results.

His ABGs were:

               Normal Value

pH      7.30   7.35-7.45
PaO2    50     90-100
PaCo2   65     40
HCO3    20     24

1. What is your interpretation of these values? Discussion

There are four major acid-base disorders: respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis. Typically the interpretation of blood gases is a simple process. The chart below gives you a "quick look" method:

Resp acidosis    PaCO2 rises and pH falls
Resp alkalosis   PaCO2 falls and pH rises
Met acidosis     HCO3 falls and pH falls
Met alkalosis    HCO3 rises and pH rises

Note that the PaO2 does not play a role in delineating acid-base imbalance. However, it is an important indicator of oxygenation and should be evaluated within the context of the acid-base balance.

2. Interpret the following blood gases.

      pH    PaCO2   HCO3   Interpretation

a.   7.50    32      28
b.   7.29    40      15
c.   7.24    60      26
d.   7.46    30      23

Here are the answers:

a) metabolic alkalosis

b) metabolic acidosis

c) respiratory acidosis

d) respiratory alkalosis

Of course, blood gas interpretation is not always so easy since the body has compensatory mechanisms which try to return the body to a normal pH. These mechanisms do not always work, especially in patients who have been in chronic acid-base imbalance.

Let us go back now and look at Mr. M. Did you interpret his blood gases as respiratory acidosis? If you did, you were correct. Patients with emphysema have lost their gas-exchange surface because of the loss of the elastic recoil of the alveoli. The result is air-trapping and destruction of the alveolar wall. These patients usually compensate over time for the CO2 retention that takes place and they become members of what is often called the 50/50 club. This means that their bodies adjust to a 50 PaO2 and a 50 PaCO2. It is when the PaCO2 begins to rise above the PaO2 that respiratory failure ensues. Even though Mr. M. is denying any shortness of breath, his ABGs indicate that soon his respiratory status will degenerate. He requires immediate intervention such as low flow oxygen therapy and breathing treatments which will help him blow off some of this excess CO2.


Mrs. H. is a 50 year old owner of a small business. She presents at the office with complaints of a burning, stabbing pain in her lower pelvis that is only relieved when she urinates. She states that she gets up frequently at night to go to the bathroom because the pain awakens her. During the day she states she has to go to the bathroom ten or fifteen times. She has decreased the amount of fluids she drinks to try to alleviate the problem but believes that it has just gotten worse. She claims to have had this problem for about two weeks.

As you would expect, the physician orders a urinalysis and urine culture and sensitivity. Here are the results of those tests:

Urine C/S reveals more than 100,000/ml bacterial colonies


Color           Dark Yellow
Appearance      Cloudy
Albumin         Negative
Bilirubin       Negative
Glucose         Negative
Ketones         Negative
Nitrite         Positive
Occult blood    Negative
pH              5.6
Odor            Fetid
Protein         1+
Specific grav   1.020
Urobilinogen    Negative Cells:
Erythrocytes    2
Leukocytes      7
Epithelium      8
Casts           Moderate
Crystals        Small amount
Bacteria        Large amount
Parasites       None

1. Next to each finding, place an N for normal or an A for abnormal.


Now let's take a look and see how many you marked correctly.


Several of the tests included in the urinalysis are normal. Those that are abnormal, are: appearance, nitrite, odor, protein, leukocytes, and bacteria.

Urine C/S

As you know, more than 100,000/ml bacterial colonies indicate a severe infection and possibly cystitis.

Let's now take a look at each of Mrs. H's abnormal findings.


Normal appearance of urine is clear to faintly hazy. Mrs. H's urine is obviously cloudy, indicating that perhaps she has bacteria and/or protein in it.


Normally we oxidize ingested nitrite and excrete it as nitrate. The presence of nitrite in the urine usually indicates a urinary tract infection with organisms that change nitrate back to nitrite.


When urine has a certain odor, it may indicate some disorder. A fishy or fetid odor indicates urinary tract infection.


Most labs will state that there should be no protein in the urine. However, some sources state that a small amount of protein in the urine can be regarded as normal. If protein is present, it should be quantified whenever the random urine sample is positive for more than a trace of protein. Mrs. H. has 1+ protein which would indicate some urinary tract disease. With her accompanying symptoms this is another piece of data to support severe cystitis.


The presence of leukocytes in the urine is abnormal. Their presence indicates inflammation and/or infection.


Normally there should be no bacteria or less than 1000/ml. Mrs. H. has a large amount of bacteria present. This finding, along with all the other abnormalities, require that a urine C/S be done.

As we put together both the lab data and the clinical signs and symptoms, we quickly recognize that Mrs. H. is probably suffering from a severe case of cystitis.

We have now covered common lab tests and ABGs. Proceed to the post-test to complete this self-study packet.

Selected References

Desai, Samir. Clinicians Guide to Laboratory Medicine. MD2B Publishers, Houston TX, 2009.

Keogh, Jim. Nursing Laboratory Diagnostic Tests Demystified. McGraw-Hill, NY, 2009.

Thompson, McFarland, Hirsch and Tucker. Mosby's Clinical Nursing, Third edition. St. Louis, Mosby-Year Book Inc., 1993.

Interpreting Common Lab Values

Post-Test and Evaluation Form

DIRECTIONS: Please complete the post-test and evaluation form. There is only one answer per question. The evaluation questions must be completed and returned with the post-test to receive a certificate.

Name: --

Date: -- Final Score: --

Please circle one answer.

1. Which of the following sets of lab tests would be ordered when trying to identify a bleeding problem?

a. Na, C1, CO2

b. K, Ca, BUN

c. PT, PTT, platelets


2. Which of the following sets of lab tests would be ordered when a patient has been experiencing fluid loss through diarrhea or vomiting?

a. PT, PTT, platelets

b. Na, CL, K, BUN

c. arterial blood gases


3. The presence of many immature neutrophils in a WBC deferential is called:

a. a shift to the right

b. thrombocytopenia

c. a shift to the left

d. leukocytopenia

4. A normal serum sodium (Na) for an adult is:

a. 135-145

b. 5,000-10,000

c. 2-5

d. 20-60

5. An elevation in the BUN without an elevation in the serum creatinine can indicate:

a. kidney disease

b. cardiac dysfunction

c. protein breakdown

d. hypervolemia

6. Which of the following blood gas values indicate respiratory acidosis?

a. pH 7.40, PaCO2 40, HCO3 24

b. pH 7.48, PaCO2 28, HCO3 16

c. pH 7.32, PaCO2 40, HCO3 16

d. pH 7.30, PaCO2 50, HCO3 23

7. Which of the following blood gas values indicate metabolic acidosis?

a. pH 7.40, PaCO2 40, HCO3 24

b. pH 7.48, PaCO2 28, HCO3 16

c. pH 7.32, PaCO2 40, HCO3 16

d. pH 7.30, PaCO2 50, HCO3 23

8. In a random urinalysis, which of the following values is considered normal?

a. trace of albumin

b. positive for nitrites

c. specific gravity of 1.020

d. positive for ketones

9. The presence of leukocytes in the urine may indicate

a. urinary tract infection

b. poor glomerular filtration

c. inadequate fluid intake

d. dysfunction of the bone marrow

10. A urine culture and sensitivity indicates clinically significant bacteriuria when there are how many bacterial colonies grown?

a. 20,000/ml

b. 50,000/ml

c. 75,000/ml

d. 100,000/ml


1. What one strategy
will you be able to use
in your work setting?

2. Was this independent study an   Yes   No
effective method of learning?

If no, please comment:             []    []

3. How long did it take you
to complete the study, the
post-test, and the evaluation
form? --

4. What other topics would you like to see addressed
in an independent study?


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Title Annotation:Independent Study
Publication:ISNA Bulletin
Date:Nov 1, 2016
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