Physiologic Variables

Age

  • Blood component values vary considerably with age.

    • Newborns exhibit higher values of red blood cells (RBC) and white blood cells (WBC) compared to adults.

    • Kidney function, such as creatinine clearance, declines with age; these functions must be adjusted for age-related calculations.

    • Hormone levels, including estrogen and growth hormone (GH), are lower in older age.

Altitude

  • Results for blood analytes, especially RBC counts, vary with altitude.

    • Increased levels of RBC, hemoglobin (Hgb), hematocrit (Hct), C-reactive protein (CRP), and uric acid at high elevations due to decreased oxygen levels, stimulating RBC production.

    • Decreased levels include urinary creatinine (affecting clearance tests) and plasma renin.

  • Analytes typically take weeks to adapt to high altitude and can return to sea level levels within days.

Dehydration

  • Defined as a decrease in total body fluid; can occur due to vomiting or diarrhea, leading to hemoconcentration.

  • Hemoconcentration affects blood components, causing increased levels of RBCs, enzymes, iron (Fe), calcium (Ca), sodium (Na+), potassium (K+), and coagulation factors.

  • Test results on dehydrated patients may not represent their normal status; obtaining specimens can be challenging.

Diet

  • Ingestion of food and drink alters blood analyte composition, with effects that are usually temporary.

  • Chewing sugarless gum can also affect various analytes.

  • Fasting (8-12 hours; water allowed unless NPO) is recommended to minimize dietary effects on analytes.

    • Reference ranges are established for fasting; deviations can lead to erroneous results.

    • Fasting beyond 12 hours could cause electrolyte imbalances or heart rhythm disturbances.

Examples of Analytes Affected by Diet

  • High-protein diets: Increased ammonia, urea, and uric acid levels.

  • Caffeine intake: Increased cortisol and adrenocorticotropic hormone (ACTH) levels.

  • Carbohydrate intake: Increased glucose and insulin levels; returns to normal in about 2 hours.

  • Excessive fluid intake: Decreased hemoglobin; can alter electrolyte balance.

  • High-fat foods: Increased lipid levels; lipemia (cloudiness of serum) can occur due to high lipid content.

Diurnal/Circadian Variations

  • Many blood components display diurnal variations influenced by factors such as posture, activity, and time of day.

    • Melatonin increases at night in darkness and decreases during the day.

    • Maximum levels of renin and thyroid-stimulating hormone (TSH) are in the predawn hours; peak cortisol occurs around 8 AM.

    • Blood analytes like aldosterone, bilirubin, cortisol, insulin, and RBCs peak in the morning, while eosinophils and glucose show lowest morning levels.

Variations in Blood Component Levels

  • Variations can exceed 50% between morning and late afternoon.

Drug Therapy

  • Several drugs alter physiological functions and the concentrations of blood analytes.

    • Chemotherapy drugs can reduce WBCs and platelets.

    • Hepatotoxic drugs such as erythromycin and acetaminophen (Tylenol) increase liver enzyme levels.

    • Opiates elevate liver and pancreatic enzymes.

    • Oral contraceptives can affect various blood test results including increasing erythrocyte sedimentation rate (ESR) and lowering vitamin B12 levels.

    • Thiazide diuretics increase calcium/glucose and decrease sodium/potassium levels.

Exercise

  • Influences numerous blood components, elevating glucose, creatinine, insulin, and potassium levels; can decrease pH and PaCO₂.

  • Skeletal muscle enzymes (CK and LDH) increase and may remain elevated post-exercise.

  • Exercise may affect lipid levels and hemostasis; vigorous exercise can elevate total cholesterol.

  • Rest for about 24 hours before blood tests is recommended to normalize results post-exercise.

Fever

  • Alters hormone levels, including increasing cortisol.

Sex

  • Biological sex results in concentration differences for blood components; men typically have higher RBC, Hgb, and Hct levels compared to women.

Intramuscular Injection

  • Recent injections can elevate CK and LDH levels; recommend drawing blood prior to injections or at least 1 hour after.

Jaundice

  • Caused by increased bilirubin concentration; interpreted as icteric specimens, potentially interfering with tests reliant on color reactions.

Position (Posture)

  • Body position can influence concentrations of components before and during blood collection.

    • Moving from supine to upright decreases plasma volume by nearly 10%.

    • Standing can notably elevate potassium levels within 30 minutes due to release from muscles; specific tests need to be collected while the patient is in the same position as when reference ranges were established.

Pregnancy

  • Physiological changes during pregnancy require test comparisons against reference ranges for pregnant populations; hemodilution during pregnancy can lead to lower RBC counts.

Smoking

  • Nicotine affects various blood components, increasing levels of cholesterol, cortisol, and glucose—especially in diabetics.

  • Smokers generally show higher WBC counts and decreased immune responses with lower immunoglobulin levels.

Stress

  • Emotional stress can transiently elevate WBC counts and may result in decreased serum iron and increased various hormone levels.

Environmental Factors

  • Temperature and humidity influences blood tests; acute heat can increase plasma volume and sweating can cause hemoconcentration.

  • Location-based environmental factors should be considered when interpreting results from off-site collections, as specimens may require protection from temperature extremes during transport.

Problems and Interventions in Phlebotomy

Problem Sites

Burns, Scars, and Tattoos

  • Avoid difficult areas as they can affect blood draw success and cause suspicious artifacts in test results.

Damaged Veins

  • Sclerosed or thrombosed veins may yield erroneous results and should be avoided.

Edema

  • Swelling can lead to inaccurate results; veins are harder to locate, may risk tissue injury during collection, and slow healing.

Hematoma

  • Occurs when blood leaks during or post-venipuncture; risks invalid tests and may alter blood flow.

Mastectomy

  • Avoid drawing from the side where a mastectomy has been performed to prevent complications related to lymphostasis.

Obesity

  • Challenges with locating veins; proper tourniquet application is essential for successful venipuncture.

Paralysis

  • Avoid venipuncture on paralyzed limbs; complications may arise due to stagnant blood flow and risk of thrombosis.

Vascular Access Devices (VADs)

  • Blood draws should not occur from extremities with any VAD according to facility policies due to contamination and dilution risks.

Types of VADs

  1. Intravenous Line (IV): Quick delivery of fluids, medications; avoid drawing blood from limbs with IVs.

  2. IV Catheter Lock: Used for medication administration; discard blood from flush solutions before collection.

  3. Arterial Line: Provides blood pressure measurement; avoid tourniquets.

  4. Dialysis Shunt, Fistula, or Graft: Permanent surgical connection of artery and vein; avoid blood draws to protect the site.

Patient Complications and Conditions

  • Be aware of any complications from prior blood draws, patient allergies, and unexpected reactions.

Allergies to Equipment and Supplies

  • Adhesive, antiseptic, and latex allergies should be managed with alternatives if necessary.

Excessive Bleeding

  • Prolonged bleeding may occur; monitor until it stops, and escalate care as needed.

Fainting (Syncope)

  • Watch for signs of fainting during draws; routine inquiries about prior fainting history can assist in preparation.

    • If fainting occurs, lie the patient down, apply pressure to the site, and ensure a safe environment until recovery.

Nausea and Vomiting

  • Manage symptoms by halting draws if necessary; provide comfort and correct any potential dehydration risks.

Pain During Venipuncture

  • Proper technique and patient education can minimize pain; if pain or nerve involvement is suspected, terminate the draw and ensure appropriate follow-through.

Petechiae

  • Tiny spots caused by capillary damage could indicate bleeding risk at the site; treat with caution.

Seizures/Convulsions

  • Should a seizure occur, support the patient, step back from the procedure, and call for assistance.

Procedural Error Risks

  • Risks include hematoma, inadvertent arterial puncture, specimen hemolysis, contamination, and improper tube usage, all of which can drastically affect test results.

Hemoconcentration

  • Caused by prolonged tourniquet use, leading to increased large molecule values; prevent by keeping the tourniquet on less than one minute.

Hemolysis

  • Occurs from damaged RBCs, resulting in pink specimens; not all hemolyzed specimens are identifiable through visual inspection.

Specimen Contamination

  • Avoid contamination by ensuring proper technique and using the correct fluids or antiseptics.

Wrong or Expired Collection Tubes

  • Verify tubes before drawing; expired tubes can lead to erroneous results or compromised test integrity.

Troubleshooting Failed Venipunctures

  • If blood flow is not established: Check needle position, tube positioning, and vessel collapse.

    • Correct techniques to prevent and address common pitfalls during blood draws are essential for ensuring valid specimen collection competition-related issues.