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Patient Preparation
Prior to blood collection, patients must be given correct instructions on how to prepare laboratory test. Utmost
care must be observed to minimize factors that may influence laboratory results.
Pre-analytical Variables-Factors contributing to the variations of results:
1. Exercise
 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 concentrations
 Transient increased in lactate, FA, ammonia
 Long-term increased in CPK, AST, LD and aldolase
 Increased in prolactin, testosterone and LH
 Elevated levels of proteins in urine (proteinuria)
 Vigorous hand exercise (fist clenching) increases potassium, lactate and phosphate
 Decreased plasma levels of FSH and LH in long distance athletes
2. Fasting
 8-14 hours: glucose, lipids and lipoproteins
 48 hrs fasting: increase bilirubin
 72 hrs fasing: may result to increase plasma TAG while glucose decreases in healthy women to 45mg/dL
 Basal state collection: glucose, cholesterol, TAG and electrolytes
 Basic metabolic panel: glucose, BUN, creatinine, Na, K, Cl, CO 2 and Ca
 Requires fasting specimen; FBS, GTT, TAG, Lipid and lipoprotein tests, gastrin and insulin
 Basal state collection is early morning blood collection, 12 hrs after the last ingestion of food.
3. Diet
 Metabolic products of food can increase in venous blood (high protein- increases urea)
 Glucose, lipids, catecholamines may show variation because of postabsorptive hormonal effects
 High CHON, Low CHO diets such as the Atkins diet- greatly increased Ketones in the urine
 Fat-rich food may increase K, ALP, TAG, and 5-HIAA
 Serotonin-rich food increase the urinary excretion of 5-HIAA
 Caffeine increases concentration of glucose; promotes the release of catecholamines from adrenal medulla
and brain tissue
 Increased in obese persons: LD, cortisol, glucose
4. Posture
 Preferred position during phlebotomy: Upright position or supine
 Patient should be seated/ supine for at least 15-20 mins before blood collection to prevent
hemoconcentration or hemodiluton
 Changing from a supine to shifting or standing position causes constriction of the blood vessels and
reduction of plasma volume- increased levels of albumin, enzymes and calcium
 Changing from sitting to supine causes shifting of water and electrolytes into tissue causing
hemoconcentration-increased levels of proteins, lipids, BUN, iron and calcium
 Changing from standing to supine causes extravascular water to transfer to the vascular system and dilutes
nondiffusable plasma constituents – decreased levels of cholesterol, triglycerides and lipoproteins.
 Significant elevation of potassium after 30 minutes of standing is due to the release of potassium from
muscles.
 Prolonged bedrest results to decreased plasma albumin due to fluid retention.
 Renin plasma level is higher when standing than supine.
Prepared by: Christine Mae Esquivel,RMT
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5. Tourniquet Application
 One minute application is recommended
 Prolonged tourniquet application results to hemoconcentration (venous stash) and anaerobiosis
 Increased levels: potassium, proteins (albumin), enzymes. lactate, cholesterol, and NH 3,
 The pressure from the tourniquet causes biological analytes to leak from the tissue cells into the blood
 Prolonged use of a tourniquet with fist exercises can increase the serum potassium level by as much as 1
mmol/L
 For accurate measurements of lactate, tourniquet use should be minimal, and the patient should not clench
his or her fist at the time of the blood draw - prolonged application of tourniquet with or without results
to elevated plasma levels of lactate
 Tourniquet application and or muscular activity decrease venous pO 2, and pH.
6. Tobacco Smoking (Nicotine)
 Increased in plasma catecholamines and cortisol.
 Increased in glucose, growth hormone, cholesterol, triglyceride, ammonia, urea, lactate, insulin and
urinary 5-HIAA
 Increased plasma nonesterified fatty acid (NEFA) concentration.
 Decreased plasma levels of vitamin B12 and elevated thiocyanate
7. Alcohol Ingestion
 Increased level of urate, triglyceride and gamma glutamyl transferase (GGT)
 It causes hypoglycemia (chronic alcoholism)
8. Stress (anxiety)
 It affects adrenal hormone secretion.
 Increased: catecholamines, cortisol. ACTH, prolactin, insulin, albumin, glucose and lactate
 Total cholesterol has been reported to increase with mild stress, and HDL cholesterol to decrease by as
much as 15%.
 It also results in hyperventilation which in turn, affects acid-base balance.
9. Drugs
 Medications affecting plasma volume can affect protein. BUN, iron and calcium concentrations.
 Therapeutic drug monitoring (TDM) specimen collection should be scheduled according to the time of
the last dose
 Hepatotoxic drugs can elevate liver function enzymes.
 Diuretics can cause decreased plasma sodium and potassium
 Opiates causes increases in liver and pancreatic enzymes.
 Analytic methods that are based on oxidation-reductlon reactions may be influenced positively or
negatively by ingested substances such as ascorbic add (vitamin C)
Physiologic Variation
 Refers to changes that occur within the body such as cyclic changes (diurnal or circadian) or those
resulting from exercise, diet, stress gender, age, drugs, posture or underlying medical conditions
 Affected by diurnal variation increased in AM: ACTH. aldosterone, cortisol and iron
decreased in PM: ACP, GH, PTH, TSH
 Affected by age (Increased levels) albumin, ALP, cholesterol and phosphorus
 Affected by gender (Increased levels: males - albumin. ALP, creatine, uric acid, cholesterol. BUN
females -HDL, iron and cholesterol
 Affected by recent food ingestion: increased levels – glucose, AG, gastrin, free Ca+2
decreased levels - electrolytes (Cl-, K+, P+), ALP, AMS
Prepared by: Christine Mae Esquivel,RMT
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TESTS AFFECTED BY DIURNAL VARIATION
Cortisol
Adrenocorticotropic hormone (ACTH)
Plasma renin activity
Aldosterone
Insulin
Growth hormone
Acid Phosphatase (ACP)
Thyroxine
Prolactin
Iron
Calcium
Peaks 4-6 am; lowest 8pm-12am;50% lowers at 8pm than 8am;
increased with stress
Lower at night; Increased with stress
Lower at night; higher standing than supine
Lower at night
Lower at night
Higher in afternoon and evening
Higher in afternoon and evening
Increases in exercise
Higher with stress; higher levels at 4 and 8am and at 8 and 10pm
Peaks early to late morning; decreases up to 30% during the day
4% decrease supine
Source: Henry’s Clinical Diagnosis and Management by Lab Methods,22 nd ed,2011
Reference:
Rodriguez,Maria Teresa.Clinical Chemistry Review Handbook for Medical Technologist.2014
Prepared by: Christine Mae Esquivel,RMT