Each blood collection situation is unique. A competent phlebotomist must not only possess the technical skills necessary to collect a quality specimen, but must also understand the numerous patient variables, complications, and procedural errors that can affect the integrity of the specimen or the health and safety of the patient to avoid or reduce any negative impact.
Factors Include:
Age
Some physiologic functions such as kidney function decrease with age in adults. For example, creatinine clearance, a kidney function test, is directly related to the age of the patient, which must be used in calculating test results.
Diet
Some laboratory tests are affected by ingestion of certain foods, which must be eliminated from the diet for several days before the test specimen is collected. For example, some methods that detect occult (hidden) blood in stool specimens also detect similar substances in meat and certain vegetables. Therefore a special diet that eliminates these foods must be followed for several days before the specimen is collected.
Fluid intake can also affect blood composition. Excessive fluid intake may cause decreased Hgb levels and alter electrolyte balance. Consumption of caffeine has been demonstrated to affect cortisol levels. Recent alcohol ingestion may also affect test values, especially glucose values.
Altitude
Decreased oxygen content of the air at higher altitudes causes the body to produce more RBC’s to fulfill the body’s oxygen requirements; the higher the altitude, the I greater the increase. Thus RBC counts and related determinations such as hemoglobin (Hgb) and hematocrit (Hct) will have higher normal ranges at higher elevations.
Daily Variations
Many blood constituents exhibit daily variations or normal fluctuations throughout the day. Factors that play a role in daily variations include activity, eating, daylight and darkness, and being awake or asleep. White blood counts, eosinophil counts, and iron levels are lower in the morning than in the afternoon. Cortisol, insulin, potassium, and testosterone levels are highest in the morning. Daily variations can be large. For example, cortisol levels and iron levels can differ by 50% or more between 8 AM and 4 PM.
Dehydration
Dehydration (a decrease in total body fluid) that occurs with persistent vomiting or diarrhea, for example, causes hemconcentration, a condition in which blood components that cannot easily leave the blood stream become concentrated as a result of the smaller plasma volume. Hemconcentration falsely increases some blood components such as RBCs, enzymes, iron, calcium, and sodium. In addition, it is often difficult to obtain a blood specimen from a dehydrated patient.
Fever
Fever affects the levels of a number of hormones. Hypoglycemia caused by fever increases insulin levels followed by a rise in glucagon levels. Fever also increases cortisol levels and may disrupt its normal diurnal variation.
Drug Therapy
Many drugs alter physiologic functions. In most instances, the effect is desired. In some individuals, however, there are unwanted physiologic effects called side effects or sensitivities. For’ example, thiazide diuretics often cause increased calcium levels and may cause low potassium levels. Chemotherapy drugs often cause a decrease in the cells of the blood, especially WBCs and platelets. Numerous drugs are toxic to the liver, causing an increase in liver enzymes such as serum glutamic-oxaloacetic transaminase (aspartate transaminase), alkaline phosphatase, and lactate dehydrogenase- (LDH/LD). Steroids and diuretics can cause pancre’atitis and an increase in serum amylase and lipase values.
Drugs may also interfere with the performance of the test in the laboratory, causing false increases or decreases in test results. Many lab test procedures are based on fluorescent, chromogenic (color-producing), peroxide-generating, or reagent-binding reactions. A drug may compete with the test reagents for the substance being tested causing a false-negative or false low result, or the drug may enhance the reaction, causing a false-positive or false high result. An acronym used for substances that interfere with the testing process is CRUD, which stands for “compounds reacting unfortunately as desired.” The College of American Pathologists (CAP) has developed guidelines for reducing interference from drugs that are known to interfere with testing procedures.
Drugs known to interfere with urine testing should be avoided for 48 to 72 hours before urine sample collection. It is up to the physician to recognize or eliminate drug interferences; however, it is helpful to the technician or technologist performing the test in the laboratory if the phlebotomist notes on the lab slip when he or she observes medication being administered just before blood collection.
Smoking
Nicotine affects a number of blood components. The extent of the effect depends upon the number of cigarettes smoked. Patients who smoke before specimen collection may have increased cortisol levels and white blood counts. Chronic smoking often leads to decreased pulmonary function and increased hemoglobin levels.
Exercise
The effect of exercise on blood composition depends upon the duration and intensity of the activity and the physical condition of the patient. However, even moderate muscular activity will elevate levels of a number of blood components, such as lactic acid, creatinine, protein, and certain enzymes. Levels of these substances return to normal soon after the activity is stopped, with the exception of enzymes such as creatine kinase and LDH, which may remain elevated 24 hours or more.
Gender
A patient’s gender or sex has a determining effect on the concentration of numerous blood components. Most differences are apparent only after sexual maturity. Differences are reflected in separate normal values for male and female patients. For example, RBC, Hgb, and Hct normal values are higher for males than females.
Pregnancy
Pregnancy causes physiologic changes in many body systems. Consequently, results of a number of laboratory tests must be compared to normal ranges established for pregnant populations. For example, body fluid increases, which are normal during pregnancy, have a diluting effect on the red blood cells, leading to lower red blood counts.
Stress
Emotional stress in the form of fear or anxiety has been shown to cause short-lived elevations in WBC counts, decreases in serum iron, and increases in adrenal hormone values. For example, studies on crying infants demonstrated marked increases in WBC counts. Counts returned to normal within 1 hour after crying stopped. For this reason, it is best if complete blood count (CBC) or WBC specimens are obtained after the infant has been sleeping or resting quietly for at least 30 minutes. If a specimen is collected while an infant is crying, it should be noted on the report.
The field of psychoneuroimmunology (PNI) deals with the study of interactions between the rain, the endocrine system, and the immune system. PNI studies have demonstrated that receptors on the cell membrane of WBC’s can sense stress in a person and react by stimulating an increase in cell numbers.
Position
A patient’s body position both before and during venipuncture influences blood composition. Going from a supine (lying down on the back) position to standing causes the water or plasma portion of the blood to filter into the tissues, resulting in a decrease in plasma volume and an increase in nonfilterable elements, or substances such as proteins, iron, calcium, and blood cells, that cannot easily pass through the walls of the blood vessels. For example, the RBC count on a patient who has been standing for approximately 15 minutes will be higher than the basal state RBC on the same patient.
Basel State
The ideal time to collect blood from a patient is when the patient is in a basal state.
Basal state is the condition of the body when a patient has refrained from strenuous exercise and has not ingested food or beverage except water for 12 hours (fasting). Collecting a basal state specimen minimizes or eliminates the effects of diet, exercise, and other controllable factors on test results and also provides the ideal specimen for establishing reference ranges or normal values for laboratory tests on inpatients.
Certain Medications
