Common Laboratory Tests

Let’s look at some nuances of 3 of most commonly ordered lab tests CBC (Complete Blood Count) BMP (Basic Metabolic Panel) Coagulation studies

CBC Complete blood count Peripheral venous blood is collected in a lavendar tube (contains the anticoagulant EDTA) and should be thoroughly mixed

What is measured? Red blood cell data –Total red blood cell count (RBC) –Hemoglobin (Hgb) –Hematocrit (Hct) White blood cell data –Total white blood cell count (WBC) –A white blood cell count differential may also be ordered Platelet Count (PLT)

Total Red Blood Cell Count Count of the number of circulating red blood cells in 1mm 3 of peripheral venous blood

Hemoglobin The hemoglobin concentration is a measure of the amount of Hgb in the peripheral blood, which reflects the number of red blood cells in the blood –Hgb constitutes over 90% of the red blood cells Decrease in Hgb concentration = –anemia Increase in Hgb concentration = –polycythemia

Hematocrit Hematocrit is a measure of the percentage of the total blood volume that is made up by the red blood cells

Centrifuged blood (normal) Red blood cells Buffy coat (WBCs and Platelets) Plasma Normal Hct in adult males 40-54% Normal Hct in adult females 34-51%

White Blood Cell Count A count of the total WBC, or leukocyte, count in 1mm 3 of peripheral blood A decrease in the number of WBCs = –Leukopenia An increase in the number of WBCs = –Leukocytosis

WBC Differential the percentage of each type of leukocyte present in a specimen is measured. –Neutrophils (includes bands) –Lymphocytes –Monocytes –Eosinophils –Basophils

Platelet Count (PLT) A count of the number of platelets (thrombocytes) per cubic milliliter of blood –A decreased number of platelets = Thrombocytopenia –An increased number of platelets = Thrombocytosis

Normal CBC CBC WBC [ ] k/ul RBC [ ] m/ul Hgb [ ] gm/dl Plt Count [ ] k/ul

One final CBC pearl Clinicians have a short-hand way to report CBC values: If we look again at the last CBC… WBC HgB HCT PLT

BMP (Basic Metabolic Panel)

BMP The BMP is a chemistry panel where multiple chemistry tests are grouped as a single profile The BMP includes electrolytes and tests of kidney function: –Sodium (Na) –Potassium (K) –Chloride (Cl) –Carbon Dioxide Content (CO2) –Blood Urea Nitrogen (BUN) –Serum Creatinine (Cr) –Serum glucose (Glu) –Total Calcium (Calcium)

BMP Peripheral venous blood can be collected in several types of tube –Light Green PST Plasma separating tube (PST) with the anticoagulant lithium heparin

Blood Urea Nitrogen The BUN measures the amount of urea nitrogen in the blood. –Urea is formed in the liver as the end product of protein metabolism and is transported to the kidneys for excretion.

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

Glucose Plasma glucose levels should be evaluated in relation to a patient’s meal postprandial fasting

Diagnosing Diabetes The criteria for the diagnosis of diabetes: –Fasting Plasma Glucose ≥110 mg/dL –2 hour Post-Prandial Glucose ≥200 mg/dl –Random Plasma Glucose >200 mg/dL in the presence of symptoms

Component Low High Units SODIUM MM/L POTASSIUM MM/L CHLORIDE MM/L BUN 7 22 MG/DL CREATININE MG/DL GLUCOSE MG/DL CALCIUM MG/DL

Coagulation Tests Coagulation tests measure your blood’s ability to clot, as well as how long it takes. Clotting disorders can cause a dangerous amount of bleeding or clotting.bleeding Conditions that cause coagulation problems include liver disease,and hemophilia. also useful in monitoring people who take medications

Types of Coagulation Tests Prothrombin Time (PT) Normal PT Values: seconds (this can vary slightly from lab to lab) measures how long it takes your blood to clot. Sometimes the PT test uses something called the international normalized ratio (INR) to compare results of different laboratories.

Types of Coagulation Tests International Normalized Ratio Blood Test-INR The INR is used to make sure the results from a PT test is the same at one lab as it is at another lab. The “normal” range for one lab would be different than a “normal” value from another lab, Normal INR Values: 1 to 2

Types of Coagulation Tests PTT(Partial Thromboplastin Time) determine if heparin (blood thinning) therapy is effective. Normal PTT Values: 30 to 45 seconds (this can value slightly from lab to lab)

Types of Coagulation Tests Platelet Count As part of a routine complete blood count (CBC); when you have episodes of unexplained or prolonged bleeding or other symptoms that may be due to a platelet disordercomplete blood count (CBC)