Table 3.

The advantages and disadvantages of PA testing using plasma and 24-hour urinary aldosterone measurements

	Plasma aldosterone	24-Hour urinary aldosterone
Variability	• Aldosterone production varies throughout the day; single spot plasma value may not reflect daily production • Risk for erroneous (false-negative) classification can be overcome by using liberalized thresholds for positive interpretation (see Figure 4a)	• Integrates aldosterone production throughout the day; less susceptible to daily variability • Only measures free and acid-labile aldosterone; does not adequately capture majority of aldosterone metabolites such as tetrahydroaldosterone that also reflect integrated production
Accessibility	• Venipuncture widely available • Assay for measurements generally widely available in locations where renin measurements also available	• 24-Hour urine collection capabilities less widely available when compared with venipuncture
Patient perspective	• Venipuncture is safe and standardized • Minimal time and effort requirement	• Requires patient education on how to collect a 24-hour urine collection adequately without over- or under-collecting • Requires patient effort and is usually inconvenient
Technical—protocol and interpretation	• Given aldosterone variability, requires a liberalized approach for interpretation (see Figure 4a) • Does not require any dietary preparation	• Requires that patient be on a relatively high-sodium balance for interpretation (see Figure 4b) • Requires measurement of urinary sodium and creatinine to ensure adequate urine collection and appropriate sodium balance • May require dietary sodium loading protocol to ensure a high-sodium balance, which adds additional effort, inconvenience, and potential risk for worsening hypertension and/or hypokalemia
Technical—laboratory	• Plasma preparation is standard • Immunoassay and LC–MS/MS techniques protocolized at laboratories where available	• Urine requires acidification prior to measurement • Following acidification, immunoassay and LC–MS/MS techniques protocolized at laboratories where available
Cost	• Variable depending on location and assay type • Cost of single plasma aldosterone measurement (in addition to renin)	• Variable depending on location and assay type • Cost of urinary acidification, urine free aldosterone, urine sodium, and urine creatinine • Generally, more expensive than a spot plasma aldosterone

Abbreviations: LC–MS, liquid chromatography–tandem mass spectrometry; PA, primary aldosteronism.