July 27, 2017
Saline Infusion Test for Hyperaldosteronism Minimize

Saline Infusion Test for hyperaldosteronism

Indication

This test is a second line test for the confirmation of Primary Aldosteronism. Patients should already have been screened with a random aldosterone:renin ratio see aldosterone sampling protocols 1. This should have found to have an elevated value (aldosterone:renin ratio > 1000 and an aldosterone >250 pmol/L). This screening test should be done following the cessation of beta blockers, diuretics, calcium channel blockers, ACE-inhibitors and angiotensin II blockers.

Contraindication

This test is contra-indicated in patients with severe heart failure and severe uncontrolled hypertension.

Principle

The principle of this test is that control of aldosterone secretion is lost and is not suppressed in response to a excessive salt and water load.

Side effects

See contraindication

Preparation

Following full assessment of the patient the following should be considered;

  • All hypertensive medication should be stopped as per Aldosterone sampling protocols -1- first line tests

  • Hypokalaemia may lead to falsely low aldosterone, hypokalaemia must be corrected prior to screening.

  • Change medication to a drug that does not effect the renin- angiotensin-aldosterone axis.

Requirements

  1. 2L 0.9% saline for IV administration

  2.  infusion pump/giving set

  3. 2 indwelling catheters

  4. 4 tubes for plasma renin and aldosterone sampling

  5. Inform biochemistry laboratory of test and requirement for urgent sampling

  6. Bed

Procedure

  1. Obtain patient consent for procedure.

  2. Start test between 08.00 and 09.30am

  3. Site indwelling catheter in antecubital fossa with good access for administration of 0.9% saline infusion.

  4. Site indwelling catheter in opposite arm for blood sampling

  5. Position patient in recumbent position prior to commencing procedure and sampling. The patient should remain recumbent throughout test.

  6. Check and record BP

  7. Take blood sample for potassium, aldosterone and renin - send to laboratory immediately

  8. Commence infusion of 2L 0.9% saline over 4 hours ie infusion pump rate 500 mL/h, total volume 2L. Observe cannulation site.

  9. At completion of infusion immediately take sample for aldosterone, renin (recumbent position)

  10. Samples for aldosterone and renin to be taken to lab immediately.

Note: samples must not be placed on ice.

Interpretation

Serum aldosterone > 140 pmol/L at the end of the study confirms a diagnosis of Primary hyperaldosteronism.

Sensitivity and Specificity

Comparison of the fludrocortisone suppression test with this iv saline loading test in a series of 100 subjects suggests that the latter is equally efficient as a diagnostic tool whilst being easier, cheaper and potentially safer (Mulatero et al 2006).

Reference

  • Mulatero P, Milan A, Fallo F, Regolisti G, Pizzolo F, Fardella C, Mosso L, Marafetti L, Veglio F, Maccario M.  Comparison of confirmatory tests for the diagnosis of primary aldosteronism. J Clin Endocrinol Metab 2006;91:2618-23.

JHB 18 July 2008

  

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