Laboratory Reference Values and Nursing Implications

Questions involving laboratory tests and procedures are included in most nursing examinations, especially the NCLEX-RN.

Patients with various medical conditions have needs that are distinct from one another. As if this is not enough of a challenge, you must also be familiar with the various laboratory tests that they must undergo and what the results of these tests may indicate.

Aside from preparing patients for the collection of specimens required for these tests, the nurse should also be aware of the safe ranges for the results of these tests. Knowledge of the normal values for these laboratory tests is important in ensuring that the healthcare team can make a safe clinical decision and that you are confident that the patient will not suffer from interventions caused by false-positive and false-negative results.

Conversely, these tests are also essential to help healthcare professionals know exactly what condition the patient has, the progress of therapies being prescribed to the patient, and whether the patient has developed any untoward reaction to treatment or is suffering from complications.

Most examinations and situations involving the care of patients with laboratory results do not include the reference (also called as “normal”) values for these tests, which means you should be familiar with these values and understand the implications of higher and lower numbers on these tests. This lecture note will help you become familiarized with the tests performed on patients and their reference values, procedures, and implications for patient care.

Different Types of Laboratory Tests

There are several types of laboratory tests being drawn for patients. These are usually grouped according to the type of specimens being drawn out and the primary purpose of obtaining them. Below are the most common:

1. Metabolic Tests. These tests are done to determine the fluid and electrolyte balance of a patient as well as to check for other metabolic parameters like blood glucose, protein, and liver enzymes. These can either be basic (also termed as BMP) or comprehensive (normally written as CMP).

a. BMP. A basic metabolic panel is usually done as part of a routine physical examination and includes 8 different tests. These are:

1. 1. 1. Glucose
      2. Calcium
      3. Sodium
      4. Chloride
      5. Potassium
      6. CO2
      7. Blood Urea Nitrogen (BUN) and
      8. Creatinine

b. CMP. Or a complete metabolic panel includes all of the tests that are part of the BMP plus liver function tests. In total, there are 15 tests that comprise the CMP: 8 from BMP and additional 7 tests, which are:

1. 1. 1. ALP
      2. AST
      3. ALT
      4. Bilirubin,
      5. Total Protein
      6. Albumin; and
      7. Globulin.

2. Complete Blood Counts. Usually written as CBC, this test aims to determine the number or amount of cells in the patient’s blood sample. Over 15 different parameters can be determined from the CBC; however, only some of them are commonly included in requests. These include:

a. Hemoglobin. the protein component of the red blood cells that help carry oxygenated blood throughout the body.

b. Hematocrit. This component determines the total amount of red blood cells present in a sample as compared to the total circulating blood volume. It is a good indicator of the hydration status of an individual.

c. White Blood Cells (WBC). The presence of WBC determines the ability of the body to fight off infections. An increased WBC count may indicate the presence of an infection, inflammation, or other conditions that may cause the body to produce additional white blood cells such as stress or an adverse effect on medications. Lowered WBC levels, on the other hand, may indicate immunosuppression. There are 5 types of WBCs that may be determined by a CBC:

1. 1. 1. Monocytes- responsible for fighting off infection and foreign bodies;
      2. Eosinophils- responsible for the allergic responses of the body and may also be increased during parasitic infections;
      3. Neutrophils- the components that help fight off bacterial infections;
      4. Basophils- also responsible for functioning during allergic responses or inflammation;
      5. Lymphocytes- plays a role in warding the body off from viral infections.

d. Red blood cell indices. These are various tests that determine the other components present in RBCs and help to diagnose further other conditions such as specific types of anemia, blood cell size, and cellular integrity.

1. Mean Corpuscular Volume (MCV). This helps determine the actual size of the red blood cells and can be useful in ruling out the presence of megaloblastic anemia.
2. Mean Corpuscular Hemoglobin (MCH). Specifically, it helps determine the amount of hemoglobin in a red blood cell and is useful in caring for patients with iron-deficiency anemia.
3. Red Cell Distribution Width (RDW). A test that helps measure the variation in the size of red blood cells in a sample.

e. Platelets. These blood components are responsible for clotting and usually measured among patients with bleeding or clotting problems. Lower values indicate bleeding tendencies, while elevated values are responsible for clotting problems.

3. Coagulation Studies. These tests help assess the presence of bleeding problems and are more specific than the platelet counts, which are done as part of the CBC. These are usually done for patients with hemolytic conditions or are taking anticoagulants.

1. PTT
2. INR
3. αPTT

4. Urine analysis (urinalysis). Usually done as part of routine tests for patients admitted, this helps determine the presence of urinary tract infections, potential kidney damage, and hydration status of a patient. It also helps determine the response of a patient with urinary tract infections to treatment regimens.

5. Arterial Blood Gases. ABGs are important to assess not only the fluid and electrolyte balance of the patients, but these values also help evaluate the presence of respiratory and metabolic conditions of patients.

6. Lipid Profile. These tests determine the amounts of cholesterol, triglycerides, and other lipoproteins in a blood sample and help determine the risks a patient has for coronary artery diseases.

7. Hemoglobin A1C. Usually performed to determine whether a patient can be diagnosed with diabetes, HbA1C measures patients’ blood glucose levels over a 3-4 month period. This time period is also the same length as the life cycle of a red blood cell. This test also helps determine a patient’s adherence to the treatment regimen or his response to therapy.

8. Tests to measure drug levels in the blood. Certain medications have to be monitored for therapeutic levels in the bloodstream and have to be watched for the risk of overdose. Common among these drugs are cardiac glycosides, lithium, carbamazepine, dilantin, and some emergency drugs.

Below is a table that includes the most commonly performed laboratory tests and normal ranges

Test	Abbreviation	Adult	Child
URINALYSIS
Color	N/A	Pale Yellow to Amber	Same as adults
Odor	N/A	Aromatic	Same as adults
Tubidity	N/A	Clear	Same as adults
Specific Gravity	Sp. Gr.	1.016 to 1.022	Same as adults
pH	pH	4.5 to 7.8	Same as adults
Glucose	N/A	>0.5 g/day	Same as adults
Red Blood Cells	RBC	less than 3 cells/HPF	Same as adults
White Blood Cells	WBC	less than or = 4 cells/HPF	Same as adults
Bacteria	N/A	None or >1000/ml	Same as adults
Casts	N/A	None to few	Same as adults
Crystals	N/A	None	Same as adults
Uric Acid	N/A	250 to 750 mg/24 hours	Same as adults
Sodium	Na	40 to 220 mEq/24 hour	Same as adults
Potassium	K	25 to 125 mEq/24 hours	Same as adults
Magnesium	Mg	7.3 – 12.2 mg/dL	Same as adults
HEMATOLOGIC – COMPLETE BLOOD COUNT (CBC)
Hemoglobin**	Hgb	Male: 14-18 g/dL Female: 12-16 g/dL Pregnant: less than 11 g/dL	1-6 yr: 9.5-14 g/dL 6-18 yr: 10-15.5 g/dL
Hematocrit**	Hct	Male: 42-52% Female: 37-47% Pregnant: >33%	1-6 yr: 30-40% 6-18 yr: 32-44%
White Blood Cell**	WBC	Both Sexes: 5-10 mm3	≤2yr: 6.2-17 mm3 ≥2 yr: 5-10 mm3
Platelet Count**	PLT	Both Sexes: 150-400 mm3	Same as adults
Mean Corpuscular Volume	MCV	80-100 fl	Same as adults
Red Blood Cell Distribution Width	RDW	11.5% to 14.5%	Same as adults
Mean Corpuscular Hemoglobin Concentration	MCHC	30-35g/dL	Same as adults
Mean Corpuscular Hemoglobin	MCH	0.4-0.5 fmol/cell	Same as adults
Neutrophils	N/A	2-8 x 10^9/L	Same as adults
Lymphocytes	N/A	1-4 x 10^9/L	Same as adults
Monocytes	N/A	0.2-0.8 x 10^9/L	Same as adults
Eosinophils	N/A	less than 0.5 x 10^9/L	Same as adults
Basophils	N/A	0–2% cells/mm³	Same as adults
ARTERIAL BLOOD GASES (ABGs)
Partial pressure of oxygen	PaO2	75 - 100 mmHg	Same as adults
Partial pressure of carbon dioxide	PaCO2	38 - 42 mmHg	Same as adults
Arterial blood pH	pH	7.38 - 7.42	Same as adults
Oxygen saturation	SaO2	94 - 100%	Same as adults
Bicarbonate	HCO3	22 - 28 mEq/L	Same as adults
HEMATOLOGIC – COAGULATION PANEL (COAGS)
Prothrombin Time	PT	Both Sexes: 11-12.5 sec Pregnant: decreased 1.5-2.5 times the normal control (on Coumadin)	Same as adults
International Normalized Ratio	INR	Normal is 0.9-1.2 seconds Desirable therapeutic level is 2-3 times the normal	Same as adults
Partial thromboplastin time	PTT	Both Sexes 60-70 sec Pregnant: decreased 1.5-2.5 times the normal control (on Heparin)	Same as adults
Activated partial thromboplastin time	APT	Both Sexes 30-40 sec 1.5-2.5 times the normal control (on Heparin)	Same as adults
BLOOD CHEMISTRY – BASIC METABOLIC PANEL (BMP)
Glucose	Glu	Both Sexes: 70-110 mg/dL	≤2 yr: 60-100 mg/dL ≥2 yr: 70-110 mg/dL
Sodium	Na	Both Sexes: 135-145 mEq/L	Same as adults
Potassium	K	Both Sexes: 3.5-5 mEq/L	3.4-4.7 mEq/l
Creatinine	N/A	Male: 0.6-1.2 mg/dL Female: 0.5-1.1 mg/dL	Child: 0.3-0.7 mg/dL
Chloride	Cl	Both Sexes: 95-105mmol/L
Blood Urea Nitrogen**	BUN	Both Sexes: 10-20 mg/dL	5-18 mg/dL
BLOOD CHEMISTRY- COMPLETE METABOLIC PANEL (CMP)
Alkaline Phosphatase	ALP	40-120 U/L
Asparatate Transaminase	AST	10-40 U/L
Alanine Transaminase	ALT	7 to 56 U/L
Bilirubin	N/A	2-20 µmol/L
Total Protein	CHON	60-80 g/L
Albumin	Alb	35-50 g/L
Globulin	N/A	IgM Component: 2.0-3.5 g/dL IgG Component: 75-300 mg/dL
BLOOD CHEMISTRY – LIPID PROFILE
Cholesterol**	N/A	Both Sexes: less than 200 mg/dL	120-200 mg/dL
BLOOD CHEMISTRY – MISCELLANEOUS
Glycosylated Hemoglobin**	Hgb A1C	less than 6%	Same as adults
THERAPEUTIC BLOOD LEVELS OF DRUGS
Digoxin	N/A	Both Sexes: 0.5-2ng/mL
Carbamazepine	N/A	Both Sexes: 4-10 mcg/mL
Gentamycin	N/A	5-10 mcg/mL (during peak); less than 2.0mcg/mL (valley)
Lithium	Li	0.8-1.5 mEq/L; critical 2.0 mEq/L
Phenobarbital	N/A	15-40 mcg/mL
Phenytoin	N/A	10-20 mcg/dL
Theophylline		10-20 mcg/dL
Tobramycin		5-10 mcg/mL (peak); 0.5-2.0 mcg/mL (valley)
Valproic Acid		50-100 mcg/mL
Vancomycin		20-40 mcg/mL (peak); 5-15 mcg/mL (trough
Table 1. Commonly-performed Laboratory Tests and Reference Values. (NOTE: Blank spaces for children’s’ results vary according to age of the child.)

Obtaining Samples from the Patient

Like any other procedure, you should remember that obtaining blood samples from a patient requires informed consent. Once this is obtained, you can then proceed to collect the specimen needed or prepare the patient for it. The following reminders should be observed:

1. Coordinate specimen collection with the laboratory. This helps in preserving the viability of the specimen and ensure that no sample goes to waste.

2. Prepare the patient for sample collection.

• If the specimen to be collected needs the patient to fast for 8-12 hours, inform him beforehand.
• Explain once again the test to be conducted and the specimen needed to be collected.
• Prepare the site where the specimen would be collected from. Cleanse with prescribed antiseptic if needed.

3. Instruct the patient what to do as the specimen is collected.

Procedures

Peripheral Vein

If collecting a peripheral vein sample:

1. Ask the patient to clench his hands and make a fist.
2. Locate the vein and pull the skin in the opposite direction.
3. Carefully insert the needle with the bevel facing up. Make sure that an angle of 15-30 degrees is observed as the needle is inserted.
4. Allow the blood to fill the syringe up to the desired level.
5. Remove the needle swiftly and apply pressure on the puncture site using a sterile gauze pad.
6. Secure the gauze with a bandage.
7. Transfer the blood sample to the prescribed tubing and label it appropriately.
8. Send the sample to the laboratory for analysis.

Central line

If the specimen is to be collected from a central line:

1. Wipe the port where the specimen is to be collected using a 70% alcohol solution.
2. Allow the port to air dry for a few seconds.
3. Draw out a few milliliters of blood from the port and discard.
4. Draw the intended amount of blood sample from the port and label it appropriately.
5. Flush out the port with 15-20mL of saline solution.
6. Send the specimen to the laboratory for analysis.

Arterial Blood Gas

If obtaining an arterial blood gas sample:

1. Instruct the patient that the vessel to be used in obtaining a sample is arterial, and the appearance of the blood may be brighter than the venous sample.
2. Place the patient’s palm up on a flat surface and position the wrist dorsiflexed at 45 degrees.
3. If the artery cannot easily be accessed at this position, place a towel or small pillow under the wrist for additional support.
4. Cleanse the puncture site with an antiseptic solution. This may either be 70% alcohol or iodine solution, depending on facility policy.
5. Air-dry the site for a few seconds and apply a local anesthetic such as a 2% lidocaine solution.
6. Palpate the pulse and puncture the site using a pre-heparinized syringe with a 23 or 25 gauge needle. Ensure that a 15-30 degree angle is obtained.
7. Draw up the recommended amount of blood sample and firmly place a sterilized gauze over the puncture site before withdrawing the needle.
8. Apply pressure over the site for at least 10-15 minutes to prevent bleeding.
9. Label the sample appropriately and send it to the laboratory for analysis.
10. If the sample cannot be immediately sent out, place it on a carrier filled with ice. The specimen would still be viable for a couple of hours, and the accuracy of the results would not be compromised.
11. Monitor the patients for signs of complications such as prolonged bleeding, infection, arteriospasm, or thrombosis.

Urine Specimen

For obtaining a urine specimen, give the patient the following instructions:

1. Inform what type of urine specimen would be collected. The most common method, however, is the midstream clean-catch specimen.
2. Instruct to clean the perineal area and cleanse the urethral opening. Use downward strokes in cleaning.
3. Ask to start the urinary stream, void a little to clean the urethral opening. (Note: the sample is not yet collected at this point).
4. Stop the flow temporarily and hold the collection container below the urethral opening and continue voiding.
5. Once the desired amount of sample is collected, seal the container.
6. Collect the specimen from the patient, label it appropriately, and send it for analysis.
7. If collecting from a catheter: Cleanse the collection port and insert the needle. Aspirate the desired amount of specimen. Transfer the specimen to the container, label, and send out for analysis.

Nursing Implications

One of the key roles that you must perform among these patients is to help ensure that the samples are collected and sent for analysis in the prescribed time. When time frames are not properly observed, this may result in specimens being discarded and the need to collect them again, causing unnecessary stress and expenses for the patient.

Moreover, you need to make sure that laboratory values are carefully monitored, and their implications for current or future care courses are considered. For example, for patients receiving treatment for urinary tract infection, they may need to have several urine samples drawn up for analysis of their response to treatment.

Also, note the patients’ reaction to the collection of specimens and ensure that any questions they may have about the test to be performed or how they are collected are answered. It is also your responsibility to inform other health team members of the results of tests being done to patients so that these are considered when making care plans for the patients. Bear in mind that the following considerations must be observed:

1. Relay all results to the physician as soon as they are available. Note significantly increased or decreased values, as well as formerly abnormal values that have normalized.

2. Compare previous results with present ones, if available. This helps in evaluating the care plan being implemented.

3. Observe patient preparation for tests to be conducted. Please note that some tests may have special considerations for patient preparation especially when they are under specific types of medication. For example:

• Occult Blood Test: Withholding iron supplements and dark-colored foods at least 3 days before testing.
• Lipid Profile, Fasting Blood Glucose: NPO at least 8-12 hours prior to drawing up of blood samples.
• Coagulation studies: Temporarily withholding anticoagulants to patients at least 72 hours prior to testing.
• Patients undergoing a test using dye: Assessment for allergy to iodine or other substances used as contrast media.

4. Determine patients’ risk for bleeding, infection, and other complications that may arise due to the collection of specimens and plan to avoid them.

5. Provide the patient and his significant others education about the testing, how the sample will be collected and the care needed to be provided to the patient before and after.

6. Ensure the viability of the sample being collected. Make sure that it is obtained from the right site, following the collection instructions, and sent to be analyzed in the prescribed time.

7. Provide care to the patient after specimen collection.

Conclusion

Laboratory tests are essential parts of the patient’s care plan because these can provide a multitude of information about the progress of care that the patient receives. It is important that you know not only how to collect them but also how they relate to the overall care plan of the patient.

Increased and decreased values are causes for concern and should be given attention, especially among patients with critical care conditions. Results should also be explained to the patient if needed, and what they can do to help ensure that their plan of care would be successfully implemented.

References

1. Basavanthappa, B., (2015). Medical Surgical Nursing. New Delhi: Jaypee Brothers Medical Publishers.
2. Billings, D. and Hensel, D., 2019. Lippincott Q & A Review For NCLEX-RN. 13th ed. St. Louis, MO., USA.: Wolters Kluwer Medical.
3. Hinkle, J.L. & Cheever, K.H. (2018). Brunner & Suddarth’s Textbook of Medical-Surgical Nursing (14th ed.). Philadelphia: Wolters Kluwer.
4. Morton, P., & Fontaine, D. (2018). Critical Care Nursing. Wolters Kluwer.
5. Potter, P.A., Perry, A.G., Stockert, P.A., & Hall, A.M. (2019). Essentials for Nursing Practice (9th ed.). St. Louis: Elsevier