Physiologic differences between groups of persons may affect test results. These deviations may be attributable to normal metabolic alterations in certain circumstances. Some examples are age (e.g., an increase in alkaline phosphataselevels in children compared with adult values), sex (e.g., higher values for serum uric acid in males than in females), race (e.g., higher values for creatine phosphokinase in African American men than European men); time of day (e.g., higher values for serum cortisol in the morning than in the evening), meals (e.g., effect on blood glucose), and body position (e.g., change in values shown in Table 1-2 due to change in posture, resulting in possible decrease in many serum test values when an ambulatory outpatient becomes a hospital inpatient).