Chemistry- Lesson 7 PDF

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LESSON 7: PATIENT PREPARATION  Pre-analytical/ pre-collection variables  In preparing a patient for phlebotomy, care should be taken to minimize physiologic factors related to activities that might influence laboratory determinations. These include diurnal variation, exercise, fasting, diet, ethan...

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LESSON 7: PATIENT PREPARATION

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Pre-analytical/ pre-collection variables 

In preparing a patient for phlebotomy, care should be taken to minimize physiologic factors related to activities that might influence laboratory determinations. These include diurnal variation, exercise, fasting, diet, ethanol consumption, tobacco smoking, drug ingestion, and posture.

DIURNAL VARIATION 

This may be encountered when testing for hormones, iron, acid phosphatase, and urinary excretion of most electrolytes such as sodium, potassium, and phosphate

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Physical activity can have different effects on analyte concentrations – volume shifts between the vascular and interstitial compartments, volume loss by sweating and changes in hormone concentration. Changes are related to increased metabolic activities for energy purposes and usually return to pre-exercise levels soon after exercise cessation. Physical activity can have different effects on analyte concentrations – volume shifts between the vascular and interstitial

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diet 

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exercise 

compartments, volume loss by sweating and changes in hormone concentration. Changes are related to increased metabolic activities for energy purposes and usually return to pre-exercise levels soon after exercise cessation.

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An individual’s diet can greatly affect laboratory test results. The effect is transient and is easily controlled. Certain foods or diet regimens may affect serum or urine constituents. Increased after eating: glucose and cholesterol Eating a meal, depending on fat content, may elevate plasma potassium, triglycerides, alkaline phosphatase, and 5hydroxyindoleacetic acid (5-HIAA). Physiologic changes may include hyperchylomicronemia, thus increasing turbidity of the serum or plasma and potentially interfering with instrument readings. Long-time vegetarian diets are reported to cause decreased concentrations of lowdensity lipoproteins (LDLs), very-lowdensity lipoproteins (VLDLs), total lipids, phospholipids, cholesterol, and triglycerides. Vitamin B12 deficiency can also occur. A high meat or other protein-rich diet may increase serum urea, ammonia, and urate levels. High protein, low carbohydrate diets, such as the Atkins diet,

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greatly increase ketones in the urine and increase the serum blood urea nitrogen (BUN). Foods with a high unsaturated-tosaturated fatty acid ratio may show decreased serum cholesterol Diet rich in purines will show an increased urate value. Foods such as bananas, pineapples, tomatoes, and avocados are rich in serotonin. When ingested, elevated urine excretion of 5-HIAA may be observed. Beverages rich in caffeine elevate plasma free fatty acids and cause catecholamine release from the adrenal medulla and brain tissue. Serum LD activity, cortisol production, and glucose increase in obesity. Plasma insulin concentration is also increased, but glucose tolerance is impaired. In obese men, testosterone concentration is reduced.

Posture/position 

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Posture of the patient during phlebotomy can have an effect on various laboratory results. Elements that are affected by postural changes are albumin, total protein, enzymes, calcium, bilirubin, cholesterol, triglycerides, and drugs bound to proteins. Patient should be seated/supine for atleast 15-20 minutes before blood collection to prevent hemodilution or hemoconcentration

IgM are lower in smokers, and IgE levels are higher.

Tourniquet application 

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It is recommended that tourniquet application should not be more than one minute. Prolonged tourniquet application results to hemoconcentration and anaerobiosis. The pressure from the tourniquet causes biological analytes to leak from the tissue cells into the blood. Increased levels: potassium (1 mmol/L), proteins (albumin), enzymes, lactate, cholesterol and ammonia Decreased levels: Venous pO2 and pH

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Tobacco smokers have high blood carboxyhemoglobin levels, plasma catecholamines, and serum cortisol. Changes in these hormones often result in decreased numbers of eosinophils, while neutrophils, monocytes, and plasma fatty free acids increase. Chronic effects of smoking lead to increased Hb concentration, erythrocyte (RBC) count, MCV, and leukocyte (WBC) count. Increased plasma levels of lactate, insulin, epinephrine, and growth hormone and urinary secretion of 5-HIAA are also seen. Vitamin B12 levels may be substantially decreased and have been reported to be inversely proportional to serum thiocyanate levels. Smoking also affects the body’s immune response. Immunoglobulin IgA, IgG, and

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Alcohol ingestion  

Increased level of urate, triglyceride and GGT Causes decreased blood sugar level (hypoglycemia) in cases of chronic alcoholism

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Stress/anxiety 

Tobacco smoking (nicotine) 

Arterial puncture technique

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Mental and physical stresses induce the production of adrenocorticotropic hormone (ACTH), cortisol, and catecholamines. Total cholesterol has been reported to increase with mild stress, and HDL cholesterol to decrease by as much as 15%. Hyperventilation affects acid-base balance and elevates leukocyte counts, serum lactate, or free fatty acids.

drugs 

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Medications affecting plasma volume can affect protein, BUN, iron and calcium concentrations Hepatotoxic drugs can elevate liver function enzymes Diuretics can cause decreased plasma sodium and potassium Opiates cause increased liver and pancreatic enzymes

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The artery to be punctured is identified by its pulsations, and the overlying skin is cleansed with 70% aqueous isopropanol solution followed by iodine. A non-anesthetized arterial puncture provides an accurate measurement of resting pH and partial pressure of carbon dioxide (pCO2) in spite of possible theoretical error caused by patient hyperventilation resulting from the pain of the arterial puncture. The use of butterfly infusion sets is NOT recommended. Using 19-gauge versus 25gauge needles does not vary the pCO2 or the partial pressure of oxygen (pO2) by more than 1 mm Hg. The amount of anticoagulant should be 0.05 mL liquid heparin (1000 IU/mL) for each milliliter of blood. Using too much heparin is probably the most common preanalytic error in blood gas measurement. Before blood is collected from the radial artery in the wrist, one should do a modified Allen test to determine whether the ulnar artery can provide collateral circulation to the hand after the radial artery puncture. The femoral artery is relatively large and easy to puncture, but one must be especially careful in older individuals because the femoral artery can bleed more than the radial or brachial. Because the bleeding site is hidden by bedcovers, it may not be noticed until bleeding is

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massive. The radial artery is more difficult to puncture, but complications occur less frequently. The major complications of arterial puncture include thrombosis, hemorrhage, and possible infection. When performed correctly, no significant complications are reported except for possible hematomas. Unacceptable sites are those that are irritated, edematous, near a wound, or in an area of an arteriovenous (AV) shunt or fistula

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Collection of blood below the IV line must be written on the laboratory requisition form to inform the staff in the chemistry section. IV fluid contamination: An increase of infused substances such as glucose, chloride, potassium and sodium with a decrease in urea and creatinine As little as 10% contamination with 5% dextrose will increase glucose in a blood sample by 500 mg/dL or more.

Notes to remember: venipuncture 

Venipuncture is accomplished using a needle/adapter assembly attached to an evacuated glass/plastic test tube with a rubber/plastic stopper. Blood may also be collected in a syringe and transferred to the appropriate specimen container (evacuated tube system). A syringe may be helpful when procuring a specimen from the hand or ankle, or from small children. In addition, patients with small or poor veins may experience collapse of veins with use of an evacuated tube system.

precaution  

The sites adjacent to IV therapy should be avoided (Stop IV line for 5-10 minutes) However, in conditions were both arms involved in therapy and the IV cannot be discontinued for a short time, a site below the IV line should be sought; the initial sample (5 mL) drawn should be discarded.

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Disinfection of the site for puncture 

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Tourniquet Application  

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If blood pressure cuff is used s a tourniquet, it is inflated up to 60 mmHg. Prior to blood collection, ask the patient for latex sensitivity to avoid allergic reactions. If a patient is allergic to latex, it is very important that all materials with such content be removed and should not be brought into the room If tourniquet is closer to the site, the vein may collapse as blood is above the intended venipuncture site. According to CLSI, when a tourniquet is used during preliminary vein selection, it should be released and reapplied after 2 minutes. Tourniquet is applied to obstruct the returns of venous blood to the heart and distend the veins, and it is discarded after each phlebotomy.

Studies have shown that reusable tourniquets have the potential to transmit bacteria, including methicillin-resistant Staphylococcus aureus (MRSA)

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NO traces of alcohol remain on the skin because it may cause hemolysis, and may contaminate glucose testing For ethanol testing, benzalkonium chloride solutions (Zephiran chloride, 1:750) should be used for skin cleansing 70% alcohol followed by an iodophor is the most common form of skin cleansing before drawing blood for culture. According to the CLSI, chlorhexidine gluconate is the recommended blood culture site disinfectant for infants 2 months and older and patients with iodine sensitivity.

Needle specifications  

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The color coding for needles indicates the gauge. The gauge of the needle is inversely related to the size of the needle, the larger the gauge number, the smaller the needle bore and length. Needle length: 1 inch or 1.5 inches - 2123 gauge ½ to ¾ inch – butterfly needle

immediately apply pressure and report the case to the supervisor

Tubes for Blood Collection 

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Blood collected in a syringe must be transferred into an evacuated tube using a syringe transfer device attached to the tube, and not by “direct transfer” from a syringe into an evacuated tube. Never transfer blood collected in an additive tube into another additive tube, even if the additives are the same. Different additives may interfere with each other or the testing process. If the additives are the same, an excess of the additive is created, which can negatively affect testing.

Other significant information  

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Wear gloves before phlebotomy and change between patients Using a needle smaller than 23 gauge increases the chance of hemolyzing the specimen If the needle or lancet touch any surface before blood collection, replace it with a new one Geriatric, oncology or other hematologic patients can have fragile veins, so it is preferable to use a winged blood collection set or syringe to minimize vessel wall injury and hemolysis Traumatic draw as a result of vessel wall injury can cause increase CK, myoglobin and potassium If a phlebotomist accidentally punctures an artery instead of a vein, he should

Sites to be avoided: 1. 2. 3. 4. 5. 6.

Intravenous lines in both arms Burned or scarred areas Areas with hematoma Thrombosed veins Edematous arms Partial/radical mastectomy on one or both arms 7. Arms with arteriovenous (AV) shunt or fistula 8. Cast on arm

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Late General Complications- serum hepatitis and AIDS

Causes of hemolysis 1. 2. 3. 4.

Complications of venipuncture Immediate Local Complication 1.

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Hemoconcentration- is an increase in the amount of formed elements in blood resulting either from a decrease or increase in plasma volume Failure of blood to enter the syringe/vacutainer tube a. Excessive pulling of plunger b. Piercing the other pole of the vein c. Transfixation of vein d. Absence of vacuum Syncope (fainting)

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Using a needle that is too small Pulling a syringe plunger back too fast Expelling the blood vigorously into a tube Forcing the blood from a syringe into an evacuated tube Shaking or mixing the tubes vigorously Performing blood collection before the alcohol has dried at the collection site

Causes of hematoma 1. 2. 3. 4. 5. 6.

Late Local Complication

Thrombosis- is an abnormal vascular condition in which thrombus develops within a blood vessel of the body. Thrombophlebitis- inflammation of a vein often accompanied by a clot which occurs as a result of trauma to the vessel wall.

The vein is fragile or too small for the needle size The needle penetrates all the way through the vein The needle is partly inserted into the vein The needle is removed while tourniquet is still on Excessive probing Pressure is not adequately applied after venipuncture

Finger or heel stick puncture

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For routine assays requiring small amounts of blood, skin puncture is a simple method by which to collect blood samples in pediatric patients. In the neonate, skin puncture of the heel is the preferred site to collect a blood sample; in older children, the finger is the preferred site. The large amount of blood required for repeated venipunctures may cause iatrogenic anemia, especially in premature infants. Skin puncture is useful in adults with (1) extreme obesity, (2) severe burns, and (3) thrombotic tendencies, with point-of-care testing or with patients performing tests at home (blood glucose). Skin puncture is often preferred in geriatric patients because the skin is thinner and less elastic; thus a hematoma is more likely to occur from a venipuncture. Length of the lancet: 1.75 mm (preferred; to avoid penetrating the bone) Depth of incision:...