Diurnal Variations in Hormones and Physiology

Diurnal Variation

• Cortisol peaks between 4-6 AM and is 50% lower at 8 PM
• Adrenocorticotropic hormone (ACTH) is lower at night and increases with stress
• Plasma renin activity is lower at night and higher when standing than supine
• Aldosterone is lower at night
• Insulin is lower at night
• Growth hormone and acid phosphatase are higher in the afternoon and evening
• Thyroxine increases with exercise
• Prolactin peaks early to late morning, decreases up to 30% during the day
• Iron levels decrease up to 30% during the day
• Calcium levels decrease by 4% when supine

Exercise

• Exercise increases lactic acid, creatine, protein, CK, AST, LDH, and potassium levels
• Prolactin levels increase in long-distance athletes
• Exercise decreases cholesterol, TAG/TGY, serum gonadotropin, and sex steroid levels in long-distance athletes

Diet

• High-protein diets elevate ammonia, urea, and uric acid levels
• Caffeine consumption increases cortisol and ACTH levels
• Carbohydrate and sugar intake increases glucose levels
• Drinking excessive amounts of water and other fluids decreases Hgb levels and causes electrolyte imbalance
• Ingestion of foods like butter, margarine, cheese, cream, and some enteral preparations increases lipid levels
• Meat, fish, iron, and horseradish consumption can lead to false positive stool occult blood test results

Stress

• Emotional stress causes transient elevations in WBCs
• Mental and physical stress induce ACTH, cortisol, and catecholamine production

Posture

• Upright position reduces plasma volume and increases protein concentration
• Albumin and calcium levels increase when changing from supine to upright position
• Changing from lying to standing can cause up to a 15% variation in total and HDL cholesterol results

Tourniquet Application

• Application increases serum enzymes, proteins, and protein-bound substances like cholesterol, calcium, and triglycerides
• Prolonged application leads to venous stasis and anaerobiosis

Tobacco Smoke

• Smoking increases cholesterol, cortisol, glucose, growth hormone, and triglyceride levels
• Chronic smoking leads to decreased pulmonary function and increased RBC counts and hemoglobin levels

Ethanol Consumption

• Increases plasma concentrations of lactate, urate, acetate, and acetaldehyde
• Increases GGT concentration and mean erythrocyte volume
• Causes hypoglycemia

Hemolysis

• Increases potassium, ammonia, iron, and enzyme levels like AST, ALT, LDH, ALP, and CK

Age

• RBC and WBC values are higher in newborns than in adults
• Kidney function decreases with age

Altitude

• RBC counts and related determinations like hemoglobin and hematocrit have higher reference ranges at higher altitudes

Dehydration

• Affects blood components like RBCs, enzymes, iron, calcium, sodium, and coagulation factors
• Difficult to obtain blood specimens from dehydrated patients

Drug Therapy

• Chemotherapy drugs decrease blood cells, especially WBCs and platelets
• Many drugs are toxic to the liver, increasing liver enzymes like ALT, AST, LDH, and decreasing clotting factors

Vascular Access

• Arterial line: a catheter placed in an artery, usually radial, for continuous blood pressure measurement and blood collection
• Arteriovenous shunt, fistula, or graft: a permanent surgical connection of an artery and vein for hemodialysis