Increased amounts of protein in the urine can be an important indicator of kidney disease. It may be the first sign of a serious problem and may appear before any other clinical symptoms. However, there are other physiologic conditions (e.g., exercise, fever) that can lead to increased protein excretion in urine. Also, there are some kidney disorders in which proteinuria is absent.

In a healthy kidney and urinary tract system, the urine contains no protein or only trace amounts. These consist of albumin (one third of normal urine protein is albumin) and globulins from the plasma. Because albumin is filtered more readily than the globulins, it is usually abundant in pathologic conditions. Therefore, the term albuminuria is often used synonymously with proteinuria.

Normally, the glomeruli prevent passage of protein from the blood to the glomerular filtrate. Therefore, the presence of protein in the urine is the single most important indication of kidney disease. If more than a trace amount of protein is found persistently in the urine, a quantitative 24-hour evaluation of protein excretion is necessary.

Postural proteinuria results from the excretion of protein by some patients when they stand or move about. This type of proteinuria is intermittent and disappears when the patient lies down. Postural proteinuria occurs in 3%–15% of healthy young adults. It is also known as orthostatic proteinuria.

Qualitative

• Negative

24-Hour Urine

• <150 mg/24 hr

Qualitative Protein Collection

1. Collect a random urine sample in a clean container and test it as soon as possible.

2. Use a protein reagent dipstick and compare the test result color with the color comparison chart provided on the reagent strip bottle. Protein can also be detected by turbidimetric methods using sulfosalicylic acid.

3. Test a new second specimen and investigate any interfering factors if one of these methods produces positive results. A 24-hour urine test may then be ordered for a quantitative measurement of protein.

1. Proteinuria occurs by two main mechanisms: damage to the glomeruli or a defect in the reabsorption process that occurs in the renal tubules.

   1. Glomerular damage

      1. Glomerulonephritis, acute and chronic

      2. Systemic lupus erythematosus (SLE)

      3. Malignant hypertension

      4. Amyloidosis

      5. DM

      6. Nephrotic syndrome

      7. Polycystic kidney disease

   2. Diminished tubular reabsorption

      1. Acute tubular necrosis

      2. Pyelonephritis, acute and chronic

      3. Cystinosis

      4. Wilson disease

      5. Fanconi syndrome (defect of proximal tubular function)

      6. Interstitial nephritis

2. In pathologic states, the level of proteinuria is rarely constant, so not every sample of urine is abnormal in patients with kidney disease, and the concentration of protein in the urine is not necessarily indicative of the severity of kidney disease.

3. Proteinuria may result from glomerular blood flow changes without the presence of a structural abnormality, as in heart failure.

4. Proteinuria may be caused by increased serum protein levels.

   1. Multiple myeloma (Bence Jones protein)

   2. Waldenström macroglobulinemia

   3. Malignant lymphoma

5. Proteinuria can occur in other nonrenal disease (“functional proteinuria”).

   1. Acute infection, septicemia

   2. Trauma, stress

   3. Leukemia, hematologic disorders

   4. Toxemia, preeclampsia of pregnancy

   5. Hyperthyroidism

   6. Vascular disease (hypertension), cardiac disease

   7. Kidney transplant rejection

   8. Central nervous system lesions

   9. Poisoning from turpentine, phosphorus, mercury, gold, lead, phenol, opiates, or other drugs

   10. Hereditary, sickle cell, oxalosis

6. Large numbers of leukocytes accompanying proteinuria usually indicate infection at some level in the urinary tract. Large numbers of both leukocytes and erythrocytes indicate a noninfectious inflammatory disease of the glomerulus. Proteinuria associated with pyelonephritis may have as many RBCs as WBCs.

7. Proteinuria does not always accompany kidney disease.

8. Proteinuria is often associated with the finding of casts on sediment examination because protein is necessary for cast formation.

Pretest Patient Care

1. Explain purpose of test, procedure for 24-hour urine collection, and interfering factors. Emphasize the importance of compliance with the procedure.

2. Allow food and fluids, but advise the patient that fluids should not be forced because very dilute urine can produce false-negative values.

3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Interfering Factors for Qualitative Protein Test

1. Because of renal vasoconstriction, the presence of a functional, mild, and transitory proteinuria is associated with:

   1. Strenuous exercise leading to urine protein values of up to 300 mg/24 hr

   2. Severe emotional stress, seizures

   3. Cold baths, exposure to very cold temperatures

2. Increased protein in urine occurs in these benign states:

   1. Fever and dehydration (salt depletion)

   2. Non–immunoglobulin E food allergies

   3. Salicylate therapy

   4. In the premenstrual period and immediately after delivery

3. False or accidental proteinuria may occur because of a mixture of pus and RBCs in the urinary tract related to infections, menstrual or vaginal discharge, mucus, or semen.

4. False-positive results can occur from incorrect use and interpretation of the color reagent strip test.

5. Alkaline, highly buffered urine can produce false-positive results on the dipstick test.

6. Very dilute urine may give a falsely low protein value.

7. Certain drugs may cause false-positive or false-negative urine protein tests (see Appendix E).

8. Radiographic contrast agents may produce false-positive results with turbidimetric measurements.