Analytes That Exhibit Diurnal Variations

Health care professionals measure analytes to determine whether the patient has any excesses or deficiencies in the blood or other fluids, which can aid in diagnosis and treatment. Many analytes vary in concentrations in an individual's blood at different times of day. These normal variations, during the course of a typical, day are called "diurnal variations."

Cortisol

• Cortisol is a blood analyte that shows changes in concentration throughout the day. Increased or decreased levels of cortisol may be related to problems with the pituitary or adrenal glands. Cortisol is manufactured by the adrenal glands. The level of cortisol increases when the pituitary gland releases a substance known as ACTH or adrenocorticotropic hormone. Cortisol levels are usually higher in the early morning and drop at night during sleep. Individuals with reversed sleep cycles may have reversed cortisol levels during the day. Individuals who do not experience a diurnal variation in their cortisol levels may have Cushing's Syndrome. Those with underproduction of cortisol may have Addison's Disease.

TSH

• Thyroid-stimulating hormone (TSH) is an analyte measured to determine whether a patient has hypothyroidism or hyperthyroidism. TSH levels in the body vary normally during the day. TSH levels are higher in the morning than in the afternoon and peak at midnight. An unusually high level of TSH can indicate an under-active thyroid or a problem with the pituitary gland. A low TSH level may indicate an overactive thyroid gland.

Phosphate

• Phosphate levels in the blood are typically measured to monitor conditions that affect the kidneys or digestive system that interfere with the absorption or excretion of phosphate. In particular, phosphate is carefully monitored in individuals with kidney failure. The level of phosphate in blood is normally lowest between 8:00 and 10:00 a.m. and is highest between the hours of 2:00 and 4:00 a.m.

Calcium

• Levels of calcium in the blood are monitored to check for a variety of problems, including disorders of the kidneys, bones, parathyroid glands, heart and nerves. Calcium and phosphate levels are generally measured at the same time because kidney disease may cause low calcium and high phosphate levels. Problems with the parathyroid are often responsible for high calcium and low phosphate levels. Blood levels of calcium are normally highest around 8:00 p.m. and lowest between 2:00 and 4:00 a.m.

PTH

• Parathyroid Hormone (PTH) levels are tested to monitor the function of the parathyroid glands. These glands regulate the amount of calcium in the body. PTH levels rise during sleep, peaking between 2:00 and 4:00 a.m., in direct opposition to the levels of calcium in the blood.

Albumin

• Low albumin levels can indicate liver or kidney disease. Low levels of albumin may also indicate a severe infection or inflammation. High albumin often signifies dehydration in an individual. Variations in albumin levels are similar to those of calcium: highest at 8:00 p.m. and lowest between 2:00 and 4:00 a.m.

Iron

• Low levels of iron in the blood may indicate anemia. High levels of iron may point to haemochromatosis, a hereditary disorder characterized by a buildup of iron in the blood. Iron levels are lowest in the evening and highest from morning until noon.

Eonsinophils

• Eonsinophils are a type of white blood cell that fights disease in the body. Blood eosinophil levels are lowest in the morning due to the release of cortisol during sleep. The amount of eosinophils in the blood may vary by as much as 40 percent during a typical daily cycle.