Plasma renin activity

Plasma renin activity (PRA), also known as the renin (active) assay or random plasma renin, is a measure of the activity of the plasma enzyme renin, which plays a major role in the body's regulation of blood pressure, thirst, and urine output. PRA is sometimes measured, specially in case of certain diseases which present with hypertension or hypotension. PRA is also raised in certain tumors.[1] A PRA measurement may be compared to a plasma aldosterone concentration as an aldosterone-to-renin ratio.

Measurement and Values

Measurement is done from a sample of venous blood using immunological measuring mechanisms like ELISA, RIA, etc. Often these are done by automated machines to minimize human error.

Considerations for variation

These values are quite variable in a normal person. Variation occur with the following:

Normal values

Reference ranges for blood tests of plasma renin activity can be given both in mass and in international units (μIU/mL or equivalently mIU/L, improperly shown as μU/mL or U/L, confusing mcU/mL used where Greek μ not available), with the former being roughly convertible to the latter by multiplying with 11.2.[2] The following table gives the lower limit (2.5th percentile) and upper limit (97.5th percentile) for plasma renin activity by mass and MCU, with different values owing to various factors of variability of reference ranges:

Unit Lower limit Upper limit
ng/(mL*hour) 0.29,[3] 1.9[4] 3.7[3][4]
μIU/mL 3.3,[2] 21[5] 41[2][5]

Results and explanations

Please go through the physiology of renin and of the renin-angiotensin system to understand why the following occur.

Higher-than-normal levels may indicate:[6][7][8][9][10]

Disease Brief Description
Addison's disease Kidneys trying to counter low aldosterone output.
Cirrhosis of the liver Reduced breakdown of Angiotensin.
Essential hypertension Just more of renin is being secreted by the kidneys.
Hemorrhage (bleeding) Kidneys trying to raise falling blood pressure.
Hypokalemia Kidneys trying to raise falling blood pressure due to reduced cardiac output.
Malignant hypertension Excessive renin is being secreted by the kidneys.
Renin-producing renal tumors Tumors can secrete substances like this. See tumor markers
Renovascular hypertension Renal vascular damage leading to reduced JGA perfusion.

Lower-than-normal levels may indicate:

Disease Brief Description
ADH therapy Leads to water retention and thus raised blood pressure.
Salt-retaining steroid therapy see above
Salt-sensitive essential hypertension see above
Primary Hyperaldosteronsim see above and direct inhibition of aldosterone on renin secretion

References

  1. ↑ Hamilton Regional Laboratory Medicine Program - Laboratory Reference Centre Manual. Renin Direct.
  2. 1 2 3 New Assays for Aldosterone, Renin and Parathyroid Hormone University of Washington, Department of Laboratory Medicine. Retrieved Mars 2011
  3. 1 2 Converted from values in μIU/mL by dividing with a factor of 11.2 μIU/mL per ng/(mL*hour), as given in: Washington, Department of Laboratory Medicine. Retrieved Mars 2011
  4. 1 2 Pratt, R.; Flynn, J.; Hobart, P.; Paul, M.; Dzau, V. (1988). "Different secretory pathways of renin from mouse cells transfected with the human renin gene". The Journal of Biological Chemistry. 263 (7): 3137–3141. PMID 2893797.
  5. 1 2 Converted from values in ng/(mL*hour) by multiplying with a factor of 11.2 μIU/mL per ng/(mL*hour), as given in: Washington, Department of Laboratory Medicine. Retrieved Mars 2011
  6. ↑ Fujino T, Nakagawa N, Yuhki K, Hara A, Yamada T, Takayama K, Kuriyama S, Hosoki Y, Takahata O, Taniguchi T, Fukuzawa J, Hasebe N, Kikuchi K, Narumiya S and Ushikubi F. (2004) Decreased susceptibility to renovascular hypertension in mice lacking the prostaglandin I2 receptor IP. J. Clin. Invest. 114:805-812.
  7. ↑ Human renin gene: structure and sequence analysis. 1984 Aug; PubMed Free text.
  8. ↑ Cloning and sequence analysis of cDNA for human renin precursor. ; PubMed.
  9. ↑ Pivotal role of the renin/prorenin receptor in angiotensin II production and cellular responses to renin. 2002 Jun; PubMed.
  10. ↑ Different secretory pathways of renin from mouse cells transfected with the human renin gene. 1988 Mar 5; PubMed Free text.

Further reading

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