TYPES OF PROTEINURIA — Proteinuria can be divided into three categories: transient (intermittent), orthostatic (related to sitting/standing or lying down), and persistent (always present).
Transient proteinuria — Transient proteinuria is by far the most common form, occurring in 4 percent of men and 7 percent of women. Transient proteinuria usually resolves without treatment. Stresses such as fever and exercise may cause transient proteinuria.
Orthostatic proteinuria — Orthostatic proteinuria occurs when protein excretion is normal when the patient is lying down but is increased when a person is sitting or standing. It occurs in 2 to 5 percent of adolescents, but is unusual in people over the age of 30. It is not known why orthostatic proteinuria occurs, but it is thought to be due to an exaggerated response to changes in position, a subtle abnormality in the glomeruli, or an exaggerated response of the circulatory system.
Orthostatic proteinuria is diagnosed by obtaining a split urine collection. This requires collecting two urine sample: one while the person is standing or sitting up (usually during the day) and another after the person has been sleeping for several hours (eg, first thing in the morning) (see "Estimating protein excretion" below). Orthostatic proteinuria is not harmful, does not require treatment, and typically disappears with age.
Persistent proteinuria — In contrast to transient and orthostatic proteinuria, persistent proteinuria is more likely to reflect underlying kidney disease or a systemic disorder. Examples of these include the following:
Heart or blood vessel disease
A disease in the body that produces abnormal proteins, which are more easily filtered by the glomeruli.
A disorder that affects the glomeruli or tubule function (eg, kidney disease).
Thus, persistent proteinuria can develop when normal blood proteins are filtered by the glomeruli (glomerular proteinuria); by filtration of abnormal proteins in the blood (overflow proteinuria); or if the tubules fail to reabsorb proteins that are normally filtered in small amounts by the glomeruli (tubular proteinuria).
The amount of protein found in the urine in proteinuria can vary widely, from a fraction of a gram to over 20 grams (20,000 milligrams) per day. As mentioned above, proteinuria is defined as protein excretion greater than 150 milligrams per day