Proteinurea in Sports

By admin Last updated Oct 20, 2023

Ovid: 5-Minute Sports Medicine Consult, The

Justin Wright

Basics

Description

Proteinuria is defined as the excretion of >150 mg/day of urinary protein.
Present in 17% of asymptomatic individuals (1)
Exercise-induced proteinuria (2):
- Transient increase in urine protein following exercise; resolves over 24–48 hr
- Relatively common, benign finding
- Proteinuria more related to exercise intensity than duration
- Due to increased glomerular permeability and decreased tubular resorption of protein as a result of reversible physiologic change in the kidney
- May also be due to a decrease in the intravascular volume from acute dehydration in athletes partaking in severe or extreme exercise
- No known long-term sequelae

Epidemiology

Proteinuria seen in up to 17% of asymptomatic individuals in general population
In the athletic population, prevalence between 18% and 100%, depending on type of activity and intensity (2)
Seen in activities with higher exercise intensity, such as boxing, wrestling, gymnastics, football, and rowing
Also seen in long-distance running, swimming, and track

Etiology

Proteins seen in the urine include:
- Plasma proteins such as albumin, transferrin, kappa, and lambda chains
- Tubular proteins such as secretory IgA, Tamm-Horsfall protein
3 categories of proteinuria (2,3):
- Glomerular:
  - Increased filtration of macromolecules across the glomerular capillary wall
  - Permeability affected by increased organic acid production, renin-angiotensin system, prostaglandins, and catecholamine activation
  - Urine protein components similar to plasma proteins
  - Seen with mild-to-moderate exercise
- Tubular:
  - Decreased resorption of filtered proteins
  - Presence of low-molecular-weight proteins
  - Due to saturation of reabsorbing mechanisms caused by a higher quantity of proteins filtered at the glomerular level
  - Seen in strenuous exercise in combination with glomerular proteinuria
- Overflow:
  - Increased production of low-molecular-weight proteins (eg, multiple myeloma)
  - Unless pre-existing condition is present, not seen in exercise-induced proteinuria

Diagnosis

The history and physical are important to differentiate benign and transient exercise-induced proteinuria from pathologic causes of proteinuria.

History

Exercise type, intensity, and duration
Prior history of renal disease
Underlying conditions that may cause proteinuria
History of recent illness
Family history of renal disease

Physical Exam

Identifying signs of underlying renal disease or process, including (4)[C]:

Elevated BP
Peripheral edema
Flank pain
Abdominal bruits

Diagnostic Tests & Interpretation

Lab

Urinalysis/dipstick:
- Inexpensive, quick screening test for proteinuria
- Standard dipstick test measures albumin concentration via a colorimetric reaction.
- False-positive results seen with alkaline urine; highly concentrated urine; gross hematuria; presence of certain medications (penicillin, sulfonamides, tolbutamide); and the presence of pus, semen, or vaginal secretions
- False-negative results seen with dilute urine or when urine proteins are nonalbumin or low molecular weight
- In exercise-induced proteinuria, dipstick may become positive within 30 min of onset of exercise and is positive for 24–48 hr.
- Usually no more than 2+ on dipstick
- For dipstick-positive proteinuria lasting >48 hr after a period of rest, further workup is required (2,4)[C].
Further workup (2,4)[C]:
- Blood urea nitrogen and creatinine
- CBC
- 24-hr urine collection for creatinine and total protein or spot protein-to-creatinine ratio

P.493

Imaging

Not routinely used in exercise-induced proteinuria
For persistent proteinuria or suspicion of renal parenchymal disease, a renal US should be performed (4)(C).

Differential Diagnosis

Transient proteinuria:
- Orthostatic proteinuria:
  - Elevated protein excretion in upright position, with normal excretion in recumbent position
  - Occurs mostly in pediatric population
  - Diagnosis made by collecting urine throughout the day, then again in the morning after recumbent all night. If orthostatic proteinuria is present, protein level in overnight sample will be within normal limits. Elevated protein in overnight sample should prompt workup for persistent proteinuria (1,4)[C].
- Fever
- Stress
- Pregnancy
Glomerular causes (eg, minimal change disease, membranous glomerulonephritis)
Tubular causes (eg, hypertensive nephrosclerosis)
Overflow (eg, multiple myeloma, hemoglobinuria)

Ongoing Care

Prognosis

There is no evidence that suggests these athletes are at increased risk for chronic renal disease or have any reason to limit their physical activity.

References

1. Carroll MF, Temte JL. Proteinuria in adults: a diagnostic approach. Am Fam Physician. 2000;62:1333–1340.

2. Bellinghieri G, Savica V, Santoro D. Renal alterations during exercise. J Ren Nutr. 2008;18:158–164.

3. Naderi AS, Reilly RF. Primary care approach to proteinuria. J Am Board Fam Med. 2008;21:569–574.

4. Kane SF, Cohen MI. Evaluation of the asymptomatic athlete with hepatic and urinalysis abnormalities. Curr Sports Med Rep. 2009;8:77–84.

Codes

ICD9

791.0 Proteinuria