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COMMON LABORATORY VALUES

COMMON LABORATORY VALUES

• Laboratory tests are an integral part of every day practice within health care.

• Lab work can help assess and diagnose patients with both acute and chronic illness.

COMMON LABORATORY TESTS

• Complete Blood Count with Differential

• Basic Metabolic Profile

• Iron Studies (TIBC, Ferritin)

• Thyroid Studies (TSH, Free t4)

• Vitamin D

• Lipid Panel


• Complete Blood Count with Differential aka “CBC with Diff”• Components of a CBC with differential:

• Total red blood cell count (RBC)• Hemoglobin (Hgb)• Hematocrit (Hct)• Mean Corpuscular volume (MCV)• Red blood cell distribution width (RDW)• Total white blood cell count (WBC)• A count (%) of each type of white blood cell (Neutrophils,

Lymphocytes, Monocytes, Eosinophils, Basophils)• Platelet count

(The Mayo Clinic, 2016; Up to Date, 2016)


• What does each finding mean?

• Total red blood cell count (RBC)- The count of the number of circulating red blood cells in 1 mm3 of peripheral venous blood.

• Hemoglobin (Hgb)- The measure of the amount of Hgbin the blood. Hgb constitutes over 90% of red blood cells.


• A decrease in Hgb concentration means the patient is anemic.• Anemia can be due to iron/B12/folate deficiency, blood

disorders or other underlying pathology.

• And increase in Hgb concentration means the patient is polycythemic. • Polycythemia can result from a large number of causes, including

cancer, lung disease, heart defects and other underlying pathologies. Smoking and many lung conditions can cause an elevated Hgb due to chronic hypoxia.


• Hematocrit- The measure of the percentage of the total blood volume that is made up by the red blood cells.

• Mean corpuscular volume (MCV)- a measure of the average size of a red blood cell. The MCV is important in classifying anemias:

• Normal MCV = normocytic anemia• Decreased MCV = microcytic anemia• Increased MCV = macrocytic anemia


• Red blood cell distribution width- An indication of the variation of the red blood cell size (anisocytosis).• In general an elevated RDW (more variation in the size of the

RBC’s) is associated with anemias with various deficiencies such as iron, B12 or folate deficiencies.


• What does each type of anemia mean?

Macrocytic Anemia-

• In adults, common causes of macrocytic anemia are:• Medications (ex: Zidovuidine, Hydroxyurea), folate deficiency,

abnormal RBC maturation (Ex: Leukemia), alcohol abuse, liver disease and hypothyroidism

• In children common causes of macrocytic anemia are: • Medications (anticonvulsants, Zidovudine and immunosuppresents),

Vitamin B12 and folate deficiencies, liver disease and hypothyroidism



Microcytic Anemia-

• In adults, common causes of microcytic anemia are:• Reduced iron availability (iron deficiency, copper deficiency), Alpha

or beta thalassemia and anemia of inflammation (chronic disease).

• In children common causes of microcytic anemia are: • Iron deficiency and thalassemia



Normocytic Anemia-

• In adults, common causes of normocytic anemia are:• Systemic disorders, chronic renal disease

• In children common causes of normocytic anemia are: • Hemolytic disease, blood loss, infection and medication


• Testing for iron deficiency:

Total Iron Binding Capacity (TIBC)- Will be elevated when a patient is anemic.

Ferritin- The cellular storage protein for iron. Iron deficiency results in a low ferritin level. Iron deficiency is the only clinical situation in which extremely low values of serum ferritin are seen


• White Blood Cells-

• Lymphocytes- Comprise about 30-40% of circulating white blood cells. • Atypical and an elevated number of lymphocytes can often be

seen following viral infections.

• Other causes of atypical lymphocytes or lymphocytosis can be lymphoma or leukemia. • If a patient has lymphocytosis in addition to thrombocytopenia,

neutropenia or anemia, this is concerning for malignancy. Patient should be referred immediately for hematology/oncology evaluation.


• Neutrophils- 40-60% of circulating white blood cells.

• Neutrophils mature in the following order: Myeloblast -> promyelocyte -> myelocyte -> metamyelocyte -> band -> mature neutrophil.

CBC/blood smear results with any cells seen that are less mature than a myelocyte are almost always associated with hematological malignancy. This warrants immediate hematology/oncology referral.

An increased number of bands is called a “left shift” and is often associated with infection.


• A low level of neutrophils is Neutropenia. A low level of neutrophils can increase the risk of infection. • Neutropenia can be caused by malignancy, immunosuppression

or be idiopathic.

• An elevated Neutrophil count (Neutrophilia) is most commonly seen with infections, stress, smoking and after exercise.


• Basophils- Comprise <1% of total WBC. An elevated basophil count is most commonly associated with myeloproliferativedisorders, hypersensitivity or inflammatory reactions, hypothyroidism, and certain infections.

• Eosinophils- Normally present in small numbers (< 5% of WBC’s). Elevated level can indicate allergic state or parasitic infection. Less commonly it can indicate a malignancy.

• Monocytes- The largest of the WBC’s. Elevated monocyte level is most commonly associated with infections, autoimmune disorders, malignancy and blood disorders.


Platelets

• Thrombocytopenia- (low platelet count)- Most commonly seen due to medications (antibiotics, antiepileptics), infection, blood disorders and liver disease.

• The presence of a very high platelet count, extremely large platelets, and/or megakaryocyte fragments is abnormal and often associated with an underlying malignancy.


• Basic Metabolic Profile• Comprised of:

• Sodium (Na)• Potassium (K)• Chloride (Cl)• Carbon Dioxide Content (CO2)• Blood Urea Nitrogen (BUN)• Serum Creatinine (Cr)• Serum Glucose (Glu)• Total Calcium (Calcium)


• Sodium (Na)• Hyponatremia- Sodium is low. This is not a common finding and is

often associated with heart failure, burns, malnutrition and severe diarrhea.

• Hypernatremia- Sodium is elevated. This is commonly associated with three main issues:

• Un-replaced water loss- diarrhea/vomiting, excessive sweating, diabetes insipidus, diabetic ketoacidosis

• water loss into cells- usually transient, typically induced by severe exercise or electroshock induced seizures.

• sodium overload- salt poisoning, hypertonic saline administration


Potassium (K)

Hypokalemia- A low level of potassium. Hypokalemia is most commonly caused by the use of diuretics, severe burns, Cushing’s syndrome, acute GI illness, hyper-aldosteronism, and renal disease.


Potassium (K)

Hyperkalemia- Elevated potassium, caused by three main mechanisms:

●Excessive increase in potassium intake●Trans-cellular movement of intracellular potassium into the extracellular space●Decreased renal excretion of potassium


Potassium (K)

●Excessive increase in potassium intake- typically caused by a high potassium containing medication or IV fluid.

●Trans-cellular movement of intracellular potassium into the extracellular space- metabolic acidosis or breakdown of normal tissue or rapid cell lysis causing potassium to be

released into the extracellular space; ex. Renal failure, tumor lysis, rhabdomyolysis.

●Decreased renal excretion of potassium- Kidney disease


Potassium (K)

*Remember: In children, psuedohyperkalemia can occur due to the small needle size which can cause the blood sample to hemolyzeresulting in a falsely elevated potassium level.


• Chloride

• Elevated Chloride Level- Dehydration, excessive salt intake, kidney disease, hyperparathyroidism

• Low Chloride Level- occurs when there is too much water in the body (ex: syndrome of inappropriate antidiuretic hormone), Addison’s disease, Metabolic Alkalosis, heart failure.


• Carbon Dioxide Content (CO2)aka “bicarb”

-Bicarbonate is an electrolyte, a negatively charged ion that is used by the body to help maintain the body's acid-base (pH) balance.

-Acidosis and alkalosis describe the abnormal conditions that result from an imbalance in the pH of the blood caused by an excess of acid or alkali (base).

-Any disease or condition that affects the lungs, kidneys, metabolism, or breathing has the potential to cause acidosis or alkalosis.


• Carbon Dioxide Content (CO2)aka “bicarb”

- Elevated CO2 can be caused by: Dehydration, Chronic diarrhea, kidney disease, Addison’s disease, Diabetic Ketoacidosis

-Low CO2 can be caused by: severe prolonged vomiting, lung disease (ex: COPD), heart failure, kidney disease


• Blood Urea Nitrogen (BUN)

• Urea is formed in the liver as the end product of protein metabolism and is transported to the kidneys for excretion.

• Nearly all renal diseases can cause an inadequate excretion of urea, which causes the blood concentration to rise above normal(thus an elevated BUN).

• The BUN is interpreted in conjunction with the creatinine test –these tests are referred to as “renal function studies”.


• Serum Creatinine

Creatinine is a catabolic product of creatine phosphate used in skeletal muscle contraction.

Creatinine, as with blood urea nitrogen, is excreted entirely by the kidneys and blood levels are therefore proportional to renal excretory function.

An elevated Creatinine level is related to kidney disease or decreased kidney function.


• Glucose- This is one of the most commonly ordered blood tests.

• Hyperglycemia (Elevated Glucose)- most commonly caused by underlying diabetes, but can also be a result of significant stress on the body or sepsis.

• Hypoglycemia (Low glucose)- Can be caused by underlying diabetes, long term or excessive fasting, underlying neurogenic disorder or severe illness/sepsis.


• Serum Calcium• The total serum calcium is a measure of both

• Free (ionized) calcium • Protein bound (usually to albumin) calcium• Calcium level is most influenced by parathyroid hormone (PTH),

vitamin D, the calcium ion, and phosphate.

Hypercalcemia (elevated calcium)- primary hyperparathyroidism and malignancy are the most common causes.

Hypocalcemia (low calcium)- Disorders of PTH and Vitamin D are the most common causes.


• Thyroid Studies• The Thyroid gland produced T3 and T4. The thyroid gland is stimulated

to produce these by Thyroid Stimulating Hormone (TSH) that is released by the pituitary gland.

●A high TSH is often accompanied by a low Free T4. This is because the body will typically increase the TSH to help increase a low T4 level. This is typically indicative of hypothyroidism.

-If TSH and T4 are both low, this is indicative of a pituitary problem.

●Serum TSH low and T3/T4 are elevated, this is indicative of hyperthyroidism.


Vitamin D

• Low Vitamin D- most commonly caused by decreased intake or absorption, reduced sun exposure.

• High Vitamin D- Very rare, typically seen when a patient has ingested a high amount of vitamin d (dose error or “fad” diet with high doses of supplements)


Thyroid Studies

The Thyroid gland produced T3 and T4. The thyroid gland is stimulated to produce these by Thyroid Stimulating Hormone (TSH) that is released by the pituitary gland.

-A high TSH is often accompanied by a low Free T4. This is because the body will typically increase the TSH to help increase a low T4 level. This is typically indicative of hypothyroidism.

-If TSH and T4 are both low, this is indicative of a pituitary problem.

-Serum TSH low and T3/T4 are elevated, this is indicative of hyperthyroidism.


Lipid Panel

A lipid panel is comprised of:

Cholesterol- Total cholesterol

Triglycerides- Fat in the blood from meals or made by liver in response to sugars and fats. This can be elevated if the patient ate a high fat meal before the blood draw.

HDL (High density lipoprotein)- the “good” cholesterol, removes excess cholesterol and moves it to the liver

LDL (Low density lipoprotein)- The “bad” cholesterol, deposits excess cholesterol in the walls of blood vessels

Non HDL- Total cholesterol minus the HDL

Chol/HDL Ratio – Total cholesterol divided by HDL.

REFERENCES

Up to Date (2016). Lab results retrieved from uptodate.com Accessed February 20th, 2016.

The Mayo Clinic (2016). Diseases and Conditions retrieved from themayoclinic.org accessed February 20th, 2016

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