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Test Catalog

Test ID: OPTU    
Orthostatic Protein, Timed Collection, Urine

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of orthostatic proteinuria

 

As a second-order test for additional characterization of proteinuria of less than 3 grams/24 hours, particularly in children or adolescents

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Orthostatic proteinuria refers to the development of increased proteinuria that develops only when the person is upright and resolves when recumbent or supine. This condition is usually seen in children, adolescents, or young adults, and accounts for the majority of cases of proteinuria in childhood.

 

Orthostatic proteinuria usually does not indicate significant underlying renal pathology, and is usually not associated with other urine abnormalities such as hypoalbuminemia, hematuria, red blood cell casts, fatty casts, etc. Orthostatic proteinuria typically resolves over time.

 

This test characterizes this condition by obtaining 2 urine collections within a 24-hour time frame, one collection obtained while the person is recumbent or supine, the other when upright.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Nighttime (supine) collection: <68 mg/8 hours

Reference values have not been established for patients <18 years of age.

 

Daytime collection: <197 mg/16 hours

Reference values have not been established for patients <18 years of age

Interpretation Provides information to assist in interpretation of the test results

A supine 8-hour urine protein excretion of less than 68 mg/8 hours together with either 1) an elevated upright (16-hour) excretion of greater than 197 mg/16 hours, or 2) a 24-hour urine protein excretion of greater than 228 mg/24 hours is considered consistent with orthostatic proteinuria.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

It is not unusual for urine protein excretion derived from supine collections to be somewhat lower than protein excretion derived from upright collections. However, orthostatic or postural proteinuria is characterized by a supine excretion rate of less than 50 mg/8 hours.

 

False-proteinuria may be due to contamination of urine with menstrual blood, prostatic secretions, or semen.

 

The urinary protein concentration may rise to 300 mg/24 hours in healthy individuals after vigorous exercise.

 

Normal newborn infants may have higher excretion of protein in urine during the first 3 days of life.

 

The presence of hemoglobin elevates protein concentration.

 

Protein electrophoresis and immunofixation may be required to characterize and interpret the proteinuria.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Rinehart BK, Terrone DA, Larmon JE, et al: A 12-hour urine collection accurately assesses proteinuria in hospitalized hypertensive gravida. J Perinatol. 1999;19:556-558

2. Adelberg AM, Miller J, Doerzbacher M, Lambers DS: Correlation of quantitative protein measurements in 8-, 12-, and 24-hour urine samples for diagnosis of preeclampsia. Am J Obstet Gynecol. 2001 Oct;185(4):804-807

3. Rytand DA, Spreiter S: Prognosis in postural (orthostatic) proteinuria: forty to fifty-year follow-up of six patients after diagnosis by Thomas Addis. N Engl J Med. 1981;305(11):618-621

4. Robinson RR: Isolated proteinuria in asymptomatic patients. Kidney Int. 1980;18:395-406

5. Dube J, Girouard J, Leclerc P et al: Problems with the estimation of urine protein by automated assays. Clin Biochem. 2005:38(5) 479-485

6. Koumantakis G, Wyndham, L: Fluorescein interference with urinary creatinine and protein measurements. Clin Chem. 1991;37(10):1799

7. Lamb EJ, Jones GRD: Kidney function tests. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:479-517

Special Instructions Library of PDFs including pertinent information and forms related to the test