Hyperaldosteronism Workup

Evaluation of a patient in whom hyperaldosteronism is suggested has several distinct stages. The finding of hypertension, hypokalemia, or both most commonly precipitates the decision to screen. The presence of these 2 features together has a 50% predictive value.

Screening for PA is recommended for patients with Joint National Commission (JNC) stage 2 (>160–179/100–109 mm Hg), stage 3 (>180/110 mm Hg), or drug-resistant hypertension (defined as systolic BP >140 and diastolic BP >90 despite treatment with 3 hypertensive medications); hypertension and spontaneous or diuretic-induced hypokalemia; hypertension with adrenal incidentaloma; or hypertension and a family history of early onset hypertension or cerebrovascular accident at a young age (< 40 y); and all hypertensive first-degree relatives of patients with PA. Additionally, in patients younger than 20 years or those with a family history of PA or stroke at a young age (< 40 y), or with an onset at a young age (eg, < 20 y), genetic testing for glucocorticoid-remediable aldosteronism is suggested. ^{[25, 28]}

The first step in the workup entails confirming that hyperaldosteronism is present and, if it is not present, excluding other conditions that produce a similar picture. The next step involves differentiating primary causes of hyperaldosteronism from secondary causes.

Aldosterone-to-renin ratio

The aldosterone-to-renin ratio (ARR)—that is, the ratio of plasma aldosterone (expressed in ng/dL) to plasma renin activity (PRA, expressed in ng/mL/h)—is the most sensitive means of differentiating primary from secondary causes of hyperaldosteronism. It can be obtained under random conditions of sodium intake.

The principle behind this test is that as aldosterone secretion rises, PRA (which measures the rate of production of angiotensin I from endogenous angiotensinogen) in ex vivo testing should fall because of sodium retention. This negative feedback response should occur when the aldosterone levels are supraphysiologic for that individual patient, and PRA may fall well before plasma aldosterone is clearly increased.

Values obtained in the upright position (ie, with the patient standing for 2 h) are more sensitive than supine test results. Patients should be encouraged not to restrict salt intake and hypokalemia should be corrected before testing because low potassium suppresses aldosterone secretion. Most authors recommend an ARR of 20-40, whereas an ARR of at least 35 has 100% sensitivity and 92.3% specificity in diagnosing PA. Some investigators require elevated aldosterone levels in addition to elevated ARR for a positive screening test for PA (usually aldosterone >15 ng/dL). Against a formal cut-off level for aldosterone are the findings of several studies, indicating that 36–48% of individuals with PA have plasma aldosterone levels between 9–16 ng/dL and approximately 20% of individuals with unilateral autonomous adrenal aldosterone production have levels less than 15 ng/dL. ^{[5, 25, 27, 28]}

The most important factors that can interfere with the diagnostic reliability of the ARR test are drugs and renal impairment (Table below). ^{[25, 28, 35]} Beta blockers can reduce PRA, leading to a falsely elevated ARR, and dihydropyridine calcium antagonists (eg, nifedipine) can reduce aldosterone levels, potentially leading to a falsely normal ARR in some patients with primary hyperaldosteronism. Diuretics tend to induce secondary hyperaldosteronism. Spironolactone, an aldosterone receptor antagonist, can raise plasma renin levels.

Table 1. Factors affecting interpretation of ARR results (Open Table in a new window)

 

Spironolactone or eplerenone, along withdiuretics, should be withheld for 6 weeks before testing.

If necessary to maintain hypertension control, patients should be treated with other antihypertensive medications that have lesser effects on the ARR (ie, verapamil slow-release, hydralazine [with verapamil slow-release, to avoid reflex tachycardia], prazosin, doxazosin, terazosin). See Table above. It is a shared opinion that dihydropyridinic calcium channel blockers do not significantly affect aldosterone secretion, causing mainly an increase in PRA, which rarely gives false negatives. ^{[36, 37]}

Βeta-blockers, ACE inhibitors, selective serotonin reuptake inhibitors, and oral contraceptives have been shown to influence the results of the test. Ideal testing conditions involve discontinuation of such medications 2 weeks prior.

Patients should also eliminate products derived from licorice root because these can interfere with 11beta-hydroxysteroid dehydrogenase, producing a state of apparent mineralocorticoid excess.

Renal impairment can lead to a high ARR in patients without primary hyperaldosteronism because fluid retention suppresses PRA and hyperkalemia stimulates aldosterone secretion.

Renin assays should be sufficiently sensitive to measure levels as low as 0.2–0.3 ng/mL/h (DRC 2 mU/L).

Recent data suggest that the random urinary aldosterone-to-creatinine ratio (UACR) might enable the diagnosis of PA in concordance with the 24-hour urinary aldosterone level (Uald-24 h). The thresholds with the best sensitivity for a specificity of 90.6% of the UACR were 3 ng/mg and that of the Uald-24 h was 20.3 mcg, in a single study. ^[38]

After a positive screening test result, subsequent testing is directed at confirming aldosterone secretory autonomy and differentiating an APA, for which surgery is currently the first-line treatment, from idiopathic hyperaldosteronism (IHA), which is usually treated medically. The possibility of GRA, which accounts for approximately 1% of cases of primary hyperaldosteronism, should be kept in mind.

Tests for confirming autonomous aldosterone secretion

Currently, US and Japanese guidelines recommend confirmatory testing in the work-up of PA; however, no test is seen as the criterion standard because of insufficient evidence.

The saline infusion test can confirm autonomous aldosterone secretion. Other tests described include the measurement of urine aldosterone excretion during oral salt loading and the fludrocortisone suppression test. All tests rely on the principle that a lack of suppression of aldosterone excretion with an intravascular expansion is indicative of aldosterone production.

Saline infusion test

Patients stay in the recumbent position for at least 1 hour before and during the infusion of 2 liters of 0.9% saline intravenously (IV) over 4 hours, starting at 8:00–9.30 AM. Blood samples for renin, aldosterone, cortisol and plasma potassium are measured at time 0 and after 4 hours, with blood BP and heart rate monitored throughout the test. Postinfusion plasma aldosterone levels less than 5 ng/dL make the diagnosis of PA unlikely. In individuals without primary hyperaldosteronism, plasma aldosterone levels should fall to less than 10 ng/dL. Plasma aldosterone values higher than 10 ng/dL confirm primary hyperaldosteronism and levels 5-10 ng/dL may be considered borderline.

Cortisol levels are taken to exclude an adrenocorticotropic hormone (ACTH)–mediated rise in aldosterone. The modified saline infusion test, performed after dexamethasone administration (0.5 mg every 6 h for 2 consecutive days) to eliminate any ACTH effect on aldosterone secretion, has been shown to have higher sensitivity compared with the classic saline infusion test in one study. ^[39] Consider the risks of fluid expansion or hypokalemia in susceptible patients.

Oral salt loading test

Patients should increase their sodium intake to more than 6 g/d for 3 days with diet and sodium chloride tabs. Potassium supplementation and daily potassium measurements are required for patients with hypokalemia. Patients perform 24-hour urine collection starting on day 3 for sodium and aldosterone. Potassium supplementation and daily potassium measurements are required for patients with hypokalemia. A 24-hour urinary aldosterone excretion of more than 12 mcg/d is consistent with PA, whereas 24-hour urinary sodium of 200 mEq/24 h indicates adequate intake. This test should not be performed in patients with uncontrolled hypertension, congestive heart failure, or arrhythmias. Renal insufficiency may confound the interpretation of the results (false negative).

Captopril test

The captopril test has also been used for screening. Its use is based on the principle that inhibition of angiotensin II production should not affect the autonomous secretion of aldosterone in PA. Patients receive 25–50 mg of oral captopril after sitting or standing for 1 h. Plasma aldosterone concentration, renin, and cortisol levels are measured before captopril administration and 1 or 2 hours after. Plasma aldosterone concentration is suppressed by 30% or more if primary hyperaldosteronism is not present. ARR is more than 30–50, plasma aldosterone concentration remains elevated (≥8.5 ng/dL), and renin remains suppressed in primary hyperaldosteronism. Differences may be seen between patients with APA and those with IHA, in that some decrease in aldosterone levels is occasionally seen in IHA. High rates of false negative or equivocal results have been reported, although this test is considered safer in patients at risk of volume overload.

Fludrocortisone suppression test

The fludrocortisone suppression test uses fludrocortisone (0.1 mg every 6 h) and salt loading. ^{[40, 41]} Patients receive 0.1 mg oral fludrocortisone every 6 hours for 4 days, together with slow-release potassium chloride supplements (every 6 h at doses sufficient to keep plasma potassium close to 4 mmol/L). Serum potassium is measured four times daily. High-sodium diet plus sodium chloride tabs are administered (30 mmol 3 times daily with meals) to maintain a urinary sodium excretion rate of at least 3 mmol/kg body weight. On day 4, plasma cortisol is measured at 7 or 8 AM and 10 AM, and plasma aldosterone concentration and renin are measured at 10 AM, with the patient in the seated position.

Upright plasma aldosterone higher than 6 ng/dL on day 4 at 10 AM confirms PA, provided that PRA is suppressed to less than 1 ng/mL/h, plasma potassium levels are normal and 10 AM plasma cortisol concentration is lower than the value obtained at 7 AM (to exclude a confounding ACTH effect). The test should not be performed in patients with uncontrolled hypertension, congestive heart failure, or arrhythmias, whereas false negative results may be obtained in renal insufficiency.

The use of the combined fludrocortisone-dexamethasone suppression test (FDST), which involves the co-administration of dexamethasone 2 mg at midnight, has been recently applied by some investigators to eliminate the stimulatory input of ACTH on aldosterone secretion, thus increasing substantially the sensitivity and specificity of the FDST and enabling the detection of milder forms of primary hyperaldosteronism. ^{[21, 34, 37, 36, 42, 43]}

Tests for differentiating aldosterone-producing adenoma from other primary hyperaldosteronism

Postural testing

Postural testing is best performed after overnight recumbency. An IV catheter is inserted at 7 AM, and baseline aldosterone, cortisol, and PRA values are obtained at 8 AM. After 2 hours of ambulation, these values are obtained again.

Typically, APAs are unresponsive to angiotensin II, and a fall in aldosterone over 2 hours is observed in parallel with reduced circadian ACTH and cortisol release. In IHA, however, a rise in aldosterone is observed, during walking compared with lying down, because upright posture stimulates renin secretion. Cortisol levels are used to validate the test; a rise in cortisol release suggests an ACTH surge, which invalidates the test. Of note, 30–50% of APAs respond to upright posture and 20% of bilateral adrenal hyperplasia are unresponsive. A diagnostic accuracy of 85% is reported.

18-hydroxycorticosterone level

Levels of 18-hydroxycorticosterone are typically elevated (>100 ng/dL) in patients with APAs and are significantly lower in patients with IHA. Although a diagnostic accuracy of 82% is reported, 18-hydroxycorticosterone levels have been noted to parallel the severity of hyperaldosteronism, and levels of aldosterone and clinical severity are greater in APAs than in IHA.

Hybrid steroid levels (18-OHF and 18-oxoF) are high (3–30 times normal) in with FH-I, normal to mildly elevated in FH-II (3–4 times normal, as in sporadic PA), and mildly to extremely high in FH-III (3–100 times normal).

Dexamethasone suppression test

In cases of bilateral aldosterone secretion or when the diagnosis is suspected on the basis of the family history, GRA can be excluded by means of a 4-day dexamethasone suppression test (using a dosage of 0.5 mg every 6 h).

The aldosterone, renin, and cortisol levels can be measured before suppression testing, after 2 days of testing, and after 4 days of testing. In patients without GRA, aldosterone levels typically fall by approximately 50% and return to the reference range by the end of testing; however, persistent suppression of aldosterone levels to less than 4 ng/dL is reported in patients with GRA. Plasma cortisol suppression (ie, < 5 mcg/dL) is used as an index of the dexamethasone effect. Compared with direct genetic testing, this test achieves a sensitivity of 92% and a specificity of 100% for the diagnosis of GRA.

Biochemically unique, markedly elevated levels of 18-oxocortisol and 18-hydroxycortisol (>100 nmol/day) are also observed in GRA and have been shown to be better than the dexamethasone suppression test for the diagnosis of GRA.

Mutation analysis for the hybrid gene that gives rise to GRA can now be accomplished by means of Southern blotting or a long polymerase chain reaction (PCR) technique. This study is likely to supersede the time-intensive dexamethasone suppression test.

In patients with FH-II, suppression of plasma aldosterone concentration may vary in response to glucocorticoid suppression test (partial, transient, blunted reduction or unresponsive). ^[44]

FH-III is a distinct disorder characterized by a paradoxical increase of aldosterone after ACTH suppression in some patients, while others demonstrate no response.

Of interest, data have shown that the titer of circulating autoantibodies directed against the second loop of the angiotensin 1 receptor (AT1AA), as well as the serum levels of parathyroid hormone, were both higher in patients with APA than those with IHA or essential hypertension, with only a small overlap between values for patients with APA and IHA. ^{[45, 46]} Hence, the determination of those parameters may provide helpful additional information for the diagnostic discrimination between these conditions.

The sensitivity and specificity of adrenal imaging with 1.25-3 mm cuts for APA is 78% and 75%, respectively. Findings may range from normal-appearing or slightly enlarged adrenal glands suggestive of bilateral adrenal hyperplasia, to small, homogeneous, hypodense nodules characteristic of APAs or, rarely, large, dense heterogeneous masses suggestive of ACC (almost always >4 cm in diameter).

In one large series, the mean APA size was 1.8 cm; however, 19% of these tumors were smaller than 1 cm. Aldosteronomas are typically lipid-rich and commonly appear as homogeneous lesions with a low Hounsfield number consistent with this high lipid content. Reported data show that if imaging alone was used for localization, 14.6% of patients would have undergone inappropriate adrenalectomy, whereas 19.1% would have been inappropriately excluded from surgery. Furthermore, in 3.9% of patients, the wrong adrenal might have been removed.

Of note, many APAs are too small to be detected and nonfunctioning incidentalomas may be mistakenly identified as causative. ^{[5, 27, 28]} Hence, the primary role of CT is to the exclude the presence of ACC. In addition, CT is also useful in defining the adrenal anatomy and localizing the right adrenal vein in preparation for adrenal venous sampling (AVS) as it enters into the inferior vena cava, thus aiding cannulation of the vein during AVS.

When a solitary adrenal mass is identified on a CT scan from a child or young adult with hyperaldosteronism, it is very likely to be the cause of the hyperaldosteronism because the prevalence of nonfunctioning adrenal adenomas is very low in childhood.

The interest in adrenal cortical scintigraphy has been renewed by the use of the new hybrid single photon emission tomography (SPET)/CT technology. Hybrid imaging permits correct localization of findings by incorporating anatomical and functional information.

The NP-59 (6b-131) iodomethyl-19-norcholesterol scan, performed with dexamethasone suppression, was a helpful diagnostic tool in the detection and lateralization of PA. SPET/CT can identify small adenomas (0.8-1.5 cm) even in patients with chronic renal disease where the biochemical diagnosis of PA is difficult. A study by Di Martino et al suggested that NP-59 testing can be used to localize primary hyperaldosteronism preoperatively when there are contraindications to adrenal venous sampling or the results of sampling are inconclusive. Basing the NP-59 test value on pathologic outcomes resulted in a sensitivity and positive predictive value of 90.9% and 83.3%, respectively. Basing the test’s performance on postoperative blood pressure control resulted in a 91.6% value for both sensitivity and positive predictive value. ^[47]

Lately, ¹¹C-metomidate PET-CT with and without dexamethasone suppression has been found to be a sensitive and specific noninvasive alternative to AVS. ^[48]  A literature review by Chen Cardenas et al indicated that as a PET-scan tracer, ¹¹C-metomidate provides a potentially useful means of identifying PA and detecting adrenocortical masses. The investigators found it to be highly specific for adrenocortical tissue and to correlate with enzyme activity. ^[49]

AVS is the criterion standard test to differentiate unilateral (APA or UAH) from bilateral disease in patients with PA; however, it requires considerable skill. It can be performed as an outpatient procedure, although younger children may need general anesthesia. Ideally, the procedure should be performed in centers with appropriate expertise. Adrenal veins are often small, and the right vein tends to be difficult to cannulate.

According to a consensus statement from an international panel of experts, AVS is not necessarily required in patients older than 40 years with marked PA and a clear unilateral adrenal adenoma and a normal contralateral adrenal gland on computed tomography imaging, in patients with unacceptable high risk of adrenal surgery (eg, multiple comorbidities in elderly patients), in patients suspected of having an adrenocortical carcinoma, or in patients with proven FH-I or with FH-III. ^[45]

ACTH may be infused into a peripheral vein (at a dosage of 50 mcg/h, starting 30 minutes before sampling) to mask the effects of confounding ACTH peaks during sampling. To reduce the risk of adrenal hemorrhage, adrenal venography is avoided.

If cosyntropin stimulation is not used, AVS is best performed in the morning after an hour of supine rest, to avoid false positive results due to diurnal fluctuation in ACTH concentrations. Additional measures, such as use of benzodiazepines and local anesthesia before venipuncture, should be taken to minimize emotional and pain-related stress.

Hypokalemia should be adequately corrected before AVS. MRAs and amiloride should be withdrawn for 4-6 weeks before AVS. Particularly, the former may allow a rise in renin secretion, which can stimulate aldosterone secretion from the unaffected contralateral adrenal gland, thus minimizing the lateralization. Peripheral α1-adrenergic receptor blockers and the long-acting dihydropyridine or nondihydropyridine calcium-channel blockers (verapamil) are recommended because of their minimal effect on renin secretion.

If cosyntropin stimulation is not used, then bilateral simultaneous AVS should be performed.

An adrenal vein cortisol-to-inferior vena cava cortisol ratio (selectivity index/SI) is used to confirm adequate cannulation of adrenal veins. The cut-off value for the SI should be 2 or higher for AVS performed under unstimulated conditions and 3 or higher for AVS performed during cosyntropin stimulation.

The lateralization index (LI), calculated from the PAC and plasma cortisol concentration (PCC) in both adrenal veins and defined as the ratio of the higher (dominant) over the lower (nondominant) PAC/PCC ratio is used for the assessment of lateralization of aldosterone hypersecretion. Although data on LI cut-off values are controversial, LI cutoff of 4 during cosyntropin stimulation and of 2 for unstimulated AVS have been recommended as the criteria to document lateralization of aldosterone excess. AVS studies using cosyntropin stimulation are considered equivocal when the LI is 2-4.

Adrenal venous sampling is not without risk and can lead to damage of the adrenal gland if not performed correctly. The major complications include adrenal vein rupture, infarction, thrombosis, groin hematoma, and adrenal hemorrhage, whereas associated complete and permanent adrenal insufficiency have been only occasionally reported. Even in experienced centers, the complication rate averages 0.5-2.5%. Similarly, failure to cannulate the right adrenal vein (≤ 20% of cases) can lead to an incorrect diagnosis of unilateral disease when, in fact, both glands are affected.

Unlike cortisol-producing adrenocortical tumors, in which the remaining ipsilateral and contralateral glands are commonly atrophic, APAs may show hyperplasia of the zona glomerulosa in the nontumorous cortex, either forming a broad zone locally or thickening the entire cortex, with tongues of glomerulosa like cortex extending inward from the subcapsular region.

This appearance has been reported in as many as one third of patients with APAs and suggests that the tumor has arisen from within an area that was hyperplastic, though to date, neither an external stimulus nor an intrinsic defect has been found.

IHA is a disease of the zona glomerulosa with a variable macroscopic appearance that can range from hyperplasia with micronodules and macronodules to hyperplasia without nodules to normal-appearing zona glomerulosa with micronodules. The glands may be normal in weight or heavy.

The normal microscopic appearance of the zona glomerulosa is of small discontinuous subcapsular nests of cells. In hyperplasia, the zona glomerulosa may contain continuous bands of cells that may be visibly thickened, either forming a continuous sheet or focally extending as tongues into the adjacent cortex. This process may be focal or diffuse and may vary from one part of the gland to another, requiring multiple sections.

GRA, or familial hyperaldosteronism (FH) type I (FH-I), results from the formation of a hybrid gene that leads to ACTH-mediated mineralocorticoid synthesis by the zona fasciculata. Histologically, evidence suggests hyperplasia of this zone in addition to the zona glomerulosa.

FH type II (FH-II) has been linked to a locus on chromosome 7p22. Histologically, evidence suggests adrenocortical hyperplasia or hypertrophy and the presence of adenomas.