eMedicine Specialties > Endocrinology > Adrenal Gland

Hyperaldosteronism, Primary: Differential Diagnoses & Workup

Author: Gabriel I Uwaifo, MBBS, Clinical and Research Attending, Assistant Professor of Medicine and Endocrinology, MedStar Clinical Research Center, MedStar Research Institute and Washington Hospital Center
Coauthor(s): Nicholas J Sarlis, MBBS, MD, PhD, FACP, Medical Director, Department of Oncology-US Medical Affairs Department, Sanofi-Aventis Pharmaceuticals
Contributor Information and Disclosures

Updated: Sep 25, 2009

Differential Diagnoses

Other Problems to Be Considered

All causes of mineralocorticoid excess and hypertension (HTN)
Low-renin essential HTN (constitutes about 40% of essential HTN)
11beta-hydroxylase deficiency variant of congenital adrenal hyperplasia (CAH)
17beta-hydroxylase deficiency variant of CAH
11beta-hydroxysteroid dehydrogenase deficiency
Licorice ingestion
Tobacco chewing
Carbenoxolone intoxication
Apparent mineralocorticoid excess (AME) syndrome
Glucocorticoid resistance
Various causes of secondary hyperaldosteronism (Unlike primary hyperaldosteronism, these causes are associated with elevated renin levels.)
Gitelman syndrome
Pseudohyperaldosteronism (Liddle syndrome)
History of exogenous mineralocorticoid ingestion or exposure
Chretien syndrome (This rare syndrome is characterized by mineralocorticoid excess and adrenocortical HTN secondary to a pituitary adenoma producing pro-opiomelanocortin [POMC].)
Deoxycorticosterone (DOC)-secreting adrenal tumors
Gordon syndrome
Renovascular ischemia
Preeclampsia (toxemia of pregnancy)

Workup

Laboratory Studies

• Individuals with primary hyperaldosteronism (PH) may present with hypokalemic metabolic alkalosis; however, as many as 38% of patients with PH may be normokalemic at presentation.⁵
  • The most important factors that predict the association of hypokalemia with PH are (1) aldosterone hypersecretion, which acts on the cortical collecting duct to stimulate potassium secretion into the tubular fluid, thus enhancing renal potassium wasting;⁹ (2) adequate intravascular volume, which enables adequate water delivery to the distal convoluted tubules and collecting ducts to enable renal potassium loss; and (3) adequate dietary sodium intake, which, in turn, increases total body potassium, renal sodium delivery, and by the countercurrent transport system thus enhancing renal potassium loss.
  • The absence of 1 or more of the physiologic circumstances described above may explain the absence of hypokalemia in many patients with proven PH.
  • The associated metabolic alkalosis in PH is due to increased renal hydrogen ion loss mediated by hypokalemia and aldosterone.
• Screening (first-tier) tests (see image below and Image 4)

• Serum potassium and bicarbonate levels - Hypokalemia and metabolic alkalosis have low sensitivities and specificities for PH when these levels are tested by themselves. Hypokalemia (potassium level <3.6 mEq/L) has a sensitivity of 75-80% while the patient is on a normal sodium diet.⁹ Typically, it is associated with mild metabolic alkalosis (serum bicarbonate level >31 mEq/L) and inappropriate kaliuresis (urinary potassium excretion >30 mmol/d).
• Mild serum hypernatremia in the 143-147 mEq/L range and mild hypomagnesemia from renal magnesium wasting - These are other associated biochemical findings in established PH.¹⁰
• Random plasma aldosterone/plasma renin activity (PRA) ratio - Because this ratio is fairly constant over many physiologic conditions, it can be used as a screening test. Normal values are less than 270 when aldosterone concentration is expressed in pmol/L, or are less than 10 when aldosterone concentration is expressed in ng/dL.
• Plasma aldosterone - PRA ratio^11,12
  • When aldosterone is measured in ng/dL and PRA is measured in ng/mL/h, a ratio greater than 20-25 has a 95% sensitivity and a 75% specificity for PH. When aldosterone is measured in pmol/L, a ratio greater than 900 is consistent with PH.
  • A major limitation of these tests is the inherent variability of aldosterone secretion due to an intrinsic circadian rhythm. Most recommendations suggest performing the test while all antihypertensives that can affect the RAS are withheld (see image below and Image 3). This can be difficult to accomplish when severe disease dictates the continuation of some medications to control hypertension (HTN) and hypokalemia during testing.

• Obtaining the ratio in the setting of chronic angiotensin-converting enzyme (ACE) inhibitor use (ie, >4 wk of use) increases the specificity of the ratio test but reduces the sensitivity.
• This test has been well validated in whites and Asians but not in other major racial groups.
• PRA after salt and water depletion and/or upright posture - In PH, PRA is less than 1 ng/mL/h and fails to rise above 2 ng/mL/h following salt and water depletion, furosemide administration, or 4 hours of erect posture. This test, along with the captopril suppression tests, has been used either as a screening test or as a confirmatory (second-tier) test (see image below and Image 5) for PH, depending on personal preferences of various groups involved in PH research. Confirmatory tests are based on the concept that aldosterone is secreted in an unregulated fashion in PH and therefore cannot be suppressed by usual physiologic regulatory inputs. In a similar fashion, PRA is chronically and tonically suppressed and cannot be stimulated.

• Captopril suppression test - This involves the oral administration of a single dose of captopril (25-50 mg). In healthy individuals, aldosterone levels suppress to less than 15 ng/dL. The test has a sensitivity of 90-100% but a specificity of only 50-80%.
  
  In a study of 135 patients who underwent captopril and losartan (an angiotensin-II receptor blocker) tests, Wu et al concluded that the values for the PRA ratio and aldosterone concentration derived with the losartan test were more accurate than those obtained through the captopril test for the diagnosis of PH.¹³ The authors found that using a PRA ratio (ng/dL per ng/mL/h) of greater than 35 and an aldosterone concentration of more than 10 ng/dL, the diagnostic specificity values for captopril and losartan were 89.1% and 93.8%, respectively, and the respective diagnostic sensitivity values were 66.2% and 84.5%.
• Confirmatory (second-tier) tests (see Image 5)
  • Serum aldosterone level
    • After 3 days of an unrestricted sodium diet and 1 hour of full recumbency, healthy individuals have aldosterone levels of less than 15 ng/dL. When serum aldosterone is elevated above 22 ng/dL and renin is suppressed, the serum aldosterone (S-Aldo) test virtually confirms the diagnosis of PH. However, because aldosterone secretion is variable, the negative and positive predictive value of a single random aldosterone level is limited.
    • As many as 40% of patients with PH have serum aldosterone levels that remain within the reference range on repeated testing, as is typically the case in essential HTN.
  • 24-hour urinary aldosterone excretion
    • The 24-hour urinary aldosterone (U-Aldo) excretion test is one of the most useful confirmatory diagnostic tools because it is an index for total daily aldosterone secretion (in a fashion similar to the 24 h urinary free cortisol [UFC], which is typically elevated in patients with Cushing syndrome).
    • In PH, the 24-hour U-Aldo is greater than 14 mcg/d (after 3 d of salt loading). Only about 7% of patients with PH have values of less than 14 mcg/d.
  • Salt loading test
    • The salt loading test can be done by using either an intravenous salt loading protocol or an oral salt loading protocol. The oral protocol calls for daily ingestion of at least 10-12 g of sodium chloride for at least 5 days before the test is performed. When the oral protocol has been met, 24-hour U-Aldo, sodium, potassium, and creatinine excretions are measured, and there is a determination of serum aldosterone and PRA. Urinary aldosterone-18-glucuronide should normally fall below 17-20 mcg/d. This test is rarely performed. The 24-hour urinary creatinine measurement validates the adequacy of the collection, while a 24-hour urinary sodium value of at least 250 mEq/d confirms an adequate salt load during the days prior to the test and therefore validates the other measurements.
    • The intravenous protocol calls for an infusion of 500 mL/h of isotonic sodium chloride solution for 4 hours (total of 2 L). The serum aldosterone level and PRA are measured at baseline, 2 hours, and 4 hours. In healthy patients, aldosterone levels are suppressed to less than 8.5 ng/dL, while PRA is suppressed to less than 0.6 ng/mL/h.
• Determination of PH subtype (third-tier) tests (see image below and Image 6)
  • Postural stimulation test
    • Aldosteronomas are associated with an anomalous decrease in aldosterone level with upright posture, in contradistinction to patients with IAH (in whom an RAS-mediated increase in aldosterone level occurs with upright posture). Moreover, a serum aldosterone level surge is expected to happen (and indeed occurs) in patients with renin-responsive adenomas (RRAs), low-renin essential HTN, and intermediate hyperaldosteronism. When abdominal computed tomography (CT) and magnetic resonance imaging (MRI) scans are combined with postural stimulation, the positive predictive value (PPV) of an abnormal postural test in predicting surgically correctable PH due to a single adenoma is 98%.
    • The standard postural test protocol involves obtaining baseline values of serum aldosterone and PRA levels, as well as the same parameters 2 hours after assuming an erect posture. Serum aldosterone levels typically rise in this setting at least 50% above baseline in healthy persons, in persons with essential HTN, and in the subgroup of patients with PH who have either IAH or RRAs. Among patients with aldosteronomas, the aldosterone levels typically do not rise or paradoxically fall to this level. The sensitivity and specificity of this test in the differential diagnosis of the main causes of PH have been reported to be as high as 80-85%.

• Furosemide (Lasix) stimulation test
  • This test is often combined with the upright posture test.
  • The typical test involves the oral administration of 40 mg of furosemide the night before and the morning of the test. On the morning of the test, the patient remains standing upright 2-3 hours, then PRA and serum aldosterone levels are assayed. The interpretation of the test results is similar to those described above for the postural stimulation test.
• Diurnal rhythm of aldosterone - The circadian rhythm of aldosterone secretion in healthy individuals parallels that of cortisol and is ACTH dependent. The lowest values are observed around 11:30 pm to midnight, and the highest values occur early in the morning around 7:30-8 am (assuming a normal sleep-wake cycle). While this is preserved in patients with aldosteronomas, it is typically lost in patients with IAH.
• Elevated levels of 18OH corticosterone and/or 18OH cortisol in plasma and urine may be found in some patients with aldosteronomas but are uncommon in IAH.^14,15

Imaging Studies

• Initial radiologic investigation in the workup of primary hyperaldosteronism (PH) is high-resolution, thin-slice (2-2.5 mm) adrenal CT scanning with contrast.
  • Because aldosteronomas tend to be small in contrast with cortisol-producing adrenocortical adenomas, only those at least 1.5 cm in diameter can be detected reliably and consistently.
  • The overall sensitivity of the test is greater than 90%, but the picture is further complicated by the many false-positive findings associated with incidentalomas, which are reported in some series to be found in up to 10% of the general population (the prevalence increases with age).¹⁶
  • The high resolution of these studies can actually be detrimental, because they often detect the hyperplasia accompanying adenomas and may result in a tendency to overdiagnose IAH. Similarly, because long-term adrenal hyperplasia is associated with nodule formation, this radiographic picture may often be confused with the diagnosis of autonomous adenomas.
• Adrenal venous sampling^17,18
  • Because this procedure is highly dependent on the availability of technically proficient interventional radiologists, it cannot be performed universally, despite the fact that it is the criterion standard for the confirmation of lateralizable aldosterone excess.
  • Adrenal venous sampling probably has its greatest utility in the setting of either totally normal adrenal imaging despite biochemical evidence for PH or settings in which bilateral adrenal pathology is present on imaging, with the biochemistry suggesting the presence of a functional aldosteronoma. The test also has utility in resolving the exact etiology in cases of PH in which discordance exists between the biochemical findings and the radiologic findings with regard to whether the PH is due to IAH or an aldosteronoma.
  • One series reported that 41% of patients with a normal adrenal CT scan who had biochemical evidence of PH actually had lateralizable disease, while 49% with bilateral micronodules on CT scan also had lateralizable disease.¹⁹ Even in cases where only a single adrenal nodule was found on imaging, when adrenal sampling was performed, it only confirmed lateralizable disease in 51-66% of cases.
  • Baseline and post-ACTH stimulation, preferably by continuous infusion at 50 mcg/h for the duration of the sampling study, blood samples are obtained simultaneously from both adrenal veins as well as from periphery veins, and the samples are assayed for aldosterone and cortisol.
  • The accuracy of the test exceeds 95% when the procedure is technically successful. If autonomous, unilateral secretion of aldosterone is present on either side, the ratio of aldosterone concentrations between the right and left adrenal veins generally exceeds 10:1. False-positive results can occur when renal artery stenosis is present; hence, renal artery stenosis needs to be thoroughly excluded, especially before a highly invasive test is performed.
  • To ensure that the catheters are adequately placed during the test, simultaneous cortisol levels need to be assayed, and aldosterone-to-cortisol ratios need to be computed.
  • The procedure is not without risks. Adrenal and iliac venous thrombosis, adrenal hemorrhage, and adrenal insufficiency are among the potential complications. Ideally, adrenal venous sampling should be performed in all patients with PH in whom the biochemical and imaging studies are inconclusive regarding the presence of lateralizable, surgically correctable disease.
• MRI
  • It is generally accepted that MRI is not superior to contrast-enhanced CT scanning for adrenal visualization. High-resolution CT scans may actually have better adrenal definition.
  • If the screening (CT scanning and/or MRI) of a patient with PH is completely normal, a 6- to 12-month treatment trial of aldosterone antagonists is generally recommended, after which the imaging studies should be repeated. Treatment with glucocorticoids may also be considered for GRA (if GRA is suspected).
• NP-59 iodocholesterol scintigraphy
  • Although fairly difficult to set up and not routinely available, this test is useful for distinguishing between adenomas and hyperplasia. In large nuclear medicine referral centers, the discriminant value of the test approaches that of adrenal venous sampling (ie, close to 90%), especially with larger tumors of 1.5 cm in diameter or larger.
  • The test results are improved by previous dexamethasone suppression of the adrenals using 0.5-1 mg of oral dexamethasone every 6 hours. In this setting, adenoma images remain visible, while hyperplastic gland images fade after a few days of dexamethasone therapy.
  • Standard scanning may produce a false-negative result for small aldosteronomas; however, the diagnostic yield can be increased by coadministration of spironolactone. This is the major diagnostic alternative to adrenal venous sampling.
• Adrenal phlebography
  • This procedure attempts to invasively visualize the venous patterns encircling adrenocortical adenomas.
  • The procedure has fallen into disrepute because of the risk of adrenal infarction.

Other Tests

• Because of the different adrenocortical zones involved in idiopathic hyperplasia, in comparison with adenomas, assays of plasma 18-hydroxycorticosterone (18-OHB) or plasma and/or urine 18-oxocortisol (18-oxo–F)/18-hydroxycortisol may be of diagnostic use.^14,15 Aldosteronomas are typically associated with 18-OHB levels greater than 100 ng/dL. Similarly, GRA (type 1 familial hyperaldosteronism), though a hyperplastic disease, is also associated with an increased production of these 18-oxo/hydroxy derivatives. This is presumed to be the case because the zona fasciculata is predominantly hyperplastic in this condition. This distinct biochemistry has also been observed in PAH but not in RRAs.
• Fludrocortisone suppression test
  • This test works on the same principle that the sodium chloride infusion or the oral salt-loading test does for confirming a diagnosis of primary hyperaldosteronism (PH). The fludrocortisone suppression test has lost much of its popularity, however, because it requires hospitalization of the patient and 4-5 days to complete. U-Aldo excretion is normally suppressed to less than 12 mcg/d, and the plasma aldosterone level is less than 8 ng/dL at the time of completion of the test in healthy patients. In patients with PH, neither the urinary aldosterone level nor the plasma aldosterone level suppresses to the above-noted thresholds.
  • Fludrocortisone is administered orally at a dose of 0.1-0.2 mg every 6 hours, along with supplemental sodium chloride and potassium. In the healthy individual, following this stimulation, the plasma aldosterone level is typically suppressed to less than 8 ng/dL, with a corresponding urinary aldosterone excretion of less than 12 mcg/d.
• Dexamethasone suppression test⁴
  • This test is relevant only in the setting of possible familial hyperaldosteronism. Customarily, in patients with PH, dexamethasone is associated with a transient reduction of plasma and urinary aldosterone levels, although not into the reference range. In the subset of patients with GRA, small doses of dexamethasone (1-2 mg/d) induce full normalization in plasma and urinary aldosterone levels. This is invariably associated with improvement in hypertension in these patients. Other reports suggest a cut-off level for plasma aldosterone of less than 4 ng/dL and/or a relative plasma aldosterone suppression of greater than 80% of the baseline for the diagnosis of GRA postdexamethasone challenge.
  • Two major variants of familial PH exist. Type 1 familial PH (also called GRA) is associated with improvement in HTN using low-dose dexamethasone. Type 2 familial PH is not dexamethasone suppressible.
• Metoclopramide (Reglan) test
  • This is a promising noninvasive test for distinguishing between aldosteronomas and IAH. It takes advantage of the differential expression of the dopamine receptors on the cell membrane of adrenocortical cells.
  • Under normal conditions, dopamine causes tonic inhibition of aldosterone secretion in vivo. This response is retained in patients with aldosteronomas and in patients with low-renin HTN but not in patients with IAH.²⁰
  • Following a 10 mg intravenous injection of metoclopramide, serum aldosterone levels increase significantly in patients with aldosteronomas, but they remain either unchanged or paradoxically reduced in patients with IAH.
• Therapeutic trial of spironolactone (Aldactone)
  • This procedure is no longer used as a diagnostic test for PH because easier and more rapid alternatives exist.
  • The therapeutic trial involves spironolactone administered orally at a dose of 100 mg 4 times per day for 5 weeks. A positive test is characterized by a decrease in diastolic blood pressure (DBP) of at least 20 mm Hg.
• ACTH stimulation test³
  • This test uses the standard 250 mcg intravenous injection.
  • In adenomatous disease, a robust aldosterone response is typically observed.
  • In IAH, the aldosterone surge is considerably feebler. The test is no longer used, because the discriminant value of the test is rather poor.
• Angiotensin-II infusion test
  • This test involves evaluating the response of PRA and serum aldosterone to a continuous angiotensin-II infusion. The response characteristics are similar to those observed in the posture tests (see Lab Studies), with an appropriate increase in aldosterone level observed in IAH but not in aldosteronomas.
  • It is less popular because of the need for continuous infusion and close hemodynamic monitoring.

Histologic Findings

Histologic findings are variable, depending on the type of primary hyperaldosteronism (PH). Typical aldosteronomas are characterized by adenomatous tissue, usually with zona fasciculata – type morphology. Most of these tumors are small (<3 cm in diameter). Most of the cells are composed of lipid-laden cells arranged in acini or cords. Associated focal and/or diffuse hyperplasia often occurs.

RRAs are characterized by zona glomerulosa – type morphology, but the only other distinctive features are predictable, unique biochemical features.

IAH is characterized by diffuse hyperplasia that may be micronodular, macronodular, or a mixture of both. The morphology of the cells is commonly akin to the zona glomerulosa.

In PAH, diffuse hyperplasia, which is unilateral and has zona fasciculata morphology, is typically observed.

PH syndrome rarely occurs in the setting of adrenal carcinoma or with the typical features of adrenal carcinoma, including mitotic figures, local invasion, and lymph node metastases.

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