Introduction to Laboratory Tests

Objectives  Introduction of basic lab tests and their use in clinical practice  Review of normal values and test interpretation  Application of the nursing process when assessing lab values

Introduction  Purpose of Understanding Basic Lab Tests  Provide education to patient and family  Plan nursing care  Communicate significant alterations in test outcomes to appropriate personnel

Labs tests do not stand alone!  Tell of:  Health or disease in the blood and tissue of a person  Help complete the picture of what’s going on with a patient  Guide treatment plans

Overview of the clinical laboratory  A place where blood, body fluids, and other biological specimens are tested, analyzed, or evaluated

Mechanics of analyzing blood proteins

Mechanics of analyzing blood proteins

Mechanics of analyzing blood proteins

Collection of blood samples and nursing responsibilities  Use correct blood tubing  Correct patient identification  Correct blood sample  Properly labeled specimen  Laboratory requisition completed and sent  Any food restrictions  Drug considerations

Patient and Clinical factors that can affect test results:  Time of day  Fasting  Postprandial  Supine, upright  Age, gender  Climate  Effects of drugs  Effects of diet

H EMATOLOGY : D EFINITION  The branch of medicine concerned with studying:  Formed elements of blood  Blood-forming tissues

H EMATOLOGY I NCLUDES :  Formed elements include:  Red blood cells  Hemoglobin (Hgb)  Hematocrit (Hct)  White blood cells  Platelet

Hematology: Purpose of Testing  Determine well-being of patient  To detect diseases:  Anemias  Leukemias  Other blood disorders  To evaluate success of treatment

H EMATOLOGY B ASICS  What does blood do?  What is blood?

Functions of Blood  Respiratory  Transports O 2 from lungs to tissues  Transports Co 2 from tissues to lungs  Nutrition  Transports nutrients from gut to tissues

Functions of Blood  Excretory  Transports waste from tissues to kidneys (urea, uric acid, water)  Regulatory  Water content of tissues  Body temperature  Protective (antibodies, WBC, etc.)

Functions of Blood  Acid-base balance  Coagulation

Composition of Blood  6% - 8% of total body weight  Normal adult’s blood volume  5 liters  Made up of cellular elements (RBC, WBC) suspended in a fluid (plasma)

Composition of Blood

Composition of Plasma:  50% - 60% of total blood volume  90% water  6 – 8% plasma proteins

Composition of Plasma  1% Electrolytes  Na+, Cl-, K+, Co 2  Other:  Glucose, amino acids  Hormones  Wastes  Blood gases

Cellular Components of Blood  Called blood cells and include:  Red blood cells (erythrocytes)  White blood cells (leukocytes)  Platelets (thrombocytes)

Cellular Components of Blood

R ED BLOOD CELLS  Most numerous  1 drop of blood contains how many RBC’s?  ___________  Live an average of 120 days  Spleen helps remove old RBC’s 250 million!

Red blood cells  Primary function:  Transport O 2 to tissues and Co 2 to lungs  Done via the hemoglobin molecule  Red color of blood  Arterial blood - bright red (oxyhemoglobin – has bound O 2 )  Venous blood – dark red (deoxyhemoglobin – has released O 2 )

Venous vs. Arterial Blood

Arterial vs. Venous circulation

Blood test for RBC  A count of actual (or estimated) number of RBC’s per cubic mm of whole blood  Normal values:  Male: 4.5 to 6.0 million/cu mm bld  Female: 4.0 to 5.5 million/cu mm bld

Clinical significance of RBC  To detect problems such as:  Anemia  Hemorrhage  Red Cell Indices  Used to determine type of anemias & includes:  MCV (Mean Corpuscular Volume  MCH (Mean corpuscular Hemoglobin  MCHC (Mean corpuscular Hemoglobin Concentration

Clinical significance of RBC  Increase:  severe COPD,  severe dehydration  Decrease  Anemia  Hemorrhage  Renal disease  More

Hemoglobin (Hb or Hbg)  Measures total amount of Hgb in blood  Most common clinical lab  Primary component of RBC  Oxygen-carrying molecule  Binds O 2 and transports from lungs to tissues  In tissues – O 2 released, Hbg binds CO 2 and carries back to lungs

Hemoglobin (Hb or Hbg)  Indirectly evaluates oxygen capacity of blood  Important to detect blood loss and anemia

Hemoglobin  Made of:  Globin (contains 4 protein chains)  Heme (attached to chains)  Contains iron  2/3 of body’s iron is in the heme

Hemoglobin  Females:  Up to middle age: 12 – 16 g/dL  After middle age: 11.7 – 13.8 g/dL  Males:  Up to middle age: 14 – 17.4 g/dL  After middle age: 12.4 – 14.9 g/dL  Critical: 20 g/dL

Hematocrit  Measure of RBC percent of total blood vol  Indirect measure of RBC # & volume  Part of “routine” testing and anemia evaluation  Normal: 36 – 48%  Critical: 60%

W HITE B LOOD C ELLS  Least numerous cells  Include a variety of cells:

White Blood Cells  Functions:  Immunity  Prevent infection  Fight invader cells  WBC’s do most of their work in the tissues; are transported via the blood

Blood test for WBC  Each microliter of blood contains 5,000 – 10,000 WBC’s  Differential cell count (“diff”)  Evaluates distribution and shape of WBC’s

WBC differential  Useful for infection, neoplasm, allergy & immunosuppression evaluations  Normal:  Neutrophils (50 – 70%)  Lymphocytes (20 – 40%)  Monocytes (2 – 8%)  Eosinophils (0 – 5%)  Basophils (0 – 2%)

Other WBC conditions:  Leukocytosis – abnormally large number of leukocytes  WBC count of ≥ 10,000 cells/mm3  Lymphocytosis – form of leukocytosis due to increase in numbers of lymphocytes  Left shift – increase in the number of immature neutrophils (bands/stabs) found in the blood

P LATELETS  Help stop bleeding  Life span of approximately 10 days  Form a plug in injured vessels  Release:  Chemicals  Enzymes

Platelets  Normal values of platelet count:  150,000 – 350,000 per mm3 (cubic mm)  Thrombocytopenia  Decreased platelet count < 100,000  Many meds can ↓ platelet count

O THER H EMATOLOGY TESTS TO MEASURE COAGULATION  Prothrombin Time (PT or Pro Time)  Measures Phase III of the clotting process (see clotting cascade)  Normal values: seconds  Produced by the liver  Requires vitamin K for synthesis  Used when patient is on Coumadin

 Partial Thromboplastin Time (PTT)  Similar to PT; used in Heparin therapy  Also detects clotting abnormalities  PTT: 60–70 seconds  APTT (Activated PTT) – similar to PTT but more sensitive  APTT: seconds

Chemistry  Measures electrolytes, chemicals, metabolic end products & substrates

Basic Metabolic Panel (BMP)  Consists of Glucose, Blood Urea Nitrogen (BUN), Creatinine, Na +, K +, Cl -, Bicarbonate (HCO 3 - ), Ca 2+

Glucose  Direct measure of blood glucose  Commonly used to evaluate diabetic pts  Part of “routine” testing  Normal: mg/dL  Critical: 400 mg/dL (♂) or 400 mg/dL (♀)

BUN  Measures urea nitrogen in blood  End product of protein metabolism (produced in liver)  Indirect measure of renal function & glomerular function (excretion)  Measure of liver metabolic function  Part of routine labs

 Usually interpreted along with Cr (less accurate than Cr for renal disease)  Normal: mg/dL  Critical: > 100 mg/dL

Creatinine  Measures serum creatinine  Catabolic product of creatine phosphate (skeletal muscle contraction)  Excreted entirely by kidneys → direct measure of renal function  Minimally affected by liver function  Elevation occurs slower than BUN

Creatinine  Normal: 0.44 – 1.03 mg/dL  Critical: > 4 mg/dL

Na +  Measures serum sodium level  Major cation in EC space  Balance between dietary intake and renal excretion  Normal: 136 – 146 mEq/L  Critical: 160 mEq/L

K+K+  Measures serum potassium level  Major cation within cell  Normal: 3.4 – 5.2 mEq/L  Critical: 6.5 mEq/L

Cl -  Measures serum chloride level  Major anion in EC space  Helps maintain electrical neutrality; follows sodium  Normal: 98 – 108 mEq/L  Critical: 115 mEq/L

HCO 3 -  Measures CO 2 content of blood  Major role in acid-base balance  Regulated by kidneys  Used to evaluate pt pH status & electrolytes  Normal: 22 – 32 mEq/L  Critical: < 6 mEq/L

Ca 2+  Measures serum calcium level  Direct measurement  Used to evaluate parathyroid function & Ca metabolism  Normal: Total = 8.3 – 10.3 mg/dL, Ionized = 4.5 – 5.6 mg/dL  Critical: Total 13 mg/dL, Ionized 7 mg/dL

Other labs:

Albumin  Measures amount of albumin in blood  Formed within liver & comprises 60% of total protein in blood  Maintains colloidal osmotic pressure & transports blood constituents  Measure of both hepatic function and nutritional state  Normal: 3.5 – 5 g/dL  ↑: dehydration  ↓: malnutrition and other

Total Protein  Measures total protein in blood  Combination of prealbumin, albumin & globulins  Normal: 6.4 – 8.3 g/dL

ALT  Found predominantly in liver  Injury/disease to parenchyma → release into blood  ID & monitor hepatocellular diseases of liver  If jaundiced, implicates liver rather than RBC hemolysis  Normal: 4 – 36 international 37°C

AST  Found in highly metabolic tissue (cardiac & skeletal muscle, liver cells)  Disease/injury → lysing of cells & release into blood  Elevation proportional to # of cells injured  Used for evaluation of suspected coronary artery disease or hepatocellular disease  Normal: 0 – 35 units/L

Urinary Analysis (UA)  Provides information about kidneys & other metabolic processes  Used for diagnosis, screening & monitoring  Frequently used to test for urinary tract infections (UTIs)

UA Normal Values  Appearance: clear  Color: amber yellow  Odor: aromatic  pH: 4.6 – 8  Protein: 0 – 8 mg/dL  Specific gravity: –  Leukocyte esterase: negative  Nitrites: none  Ketones: none

UA Normal Values cont.  Bilirubin: none  Urobilinogen: 0.01 – 1 Ehrlich unit/mL  Crystals: none  Casts: none  Glucose: negative  White Blood Cells: 0 – 4/low-power field  WBC casts: none  Red Blood Cells (RBCs): ≤ 2  RBC casts: none

General Nursing Implications  Report any abnormal findings to the health care provider  Educate the patient and/or family  Prepare the patient for further testing or surgery, as indicated  Provide emotional support to the patient and family

Case study  Your patient, Mr. Jones, a 54-year- old male was admitted this morning with GI bleeding. It is 11:30 p.m. and his CBC results from earlier this evening (5:00 p.m.) have just been placed on his chart. The results reported on the lab slip are within “normal” range.

 However, the results are in the “low normal” range. The RBC count is 4.6, the total Hgb is 14.5, and Hct is 42.5.

Case study continues  The patient has become slightly lethargic, sleepy, and slightly pale. The lab test results were not called to the doctor because they were within the normal limits. However, this was at 5:00 p.m. and it is now 11:30 p.m. What do you do? Do you call the doctor at 11:30 p.m.? Do you wait until the morning when another CBC is scheduled?

Important “Rules of Thumb:”  Even with “normal” results, still assess the patient for:  Abnormal signs/symptoms  If abnormal:  Check for adverse S/S related to the abnormal values

Important “Rules of Thumb:”  Look for “trends” in lab results  Example:  Hemoglobin – normal but slowly going down.  What could this indicate? _____________________ Slow GI bleed

Important “Rules of Thumb:”  Assess for patient factors that may indicate a problem  Use your assessment skills and nursing process at all times; do not rely solely on the lab value.