SUSPUP and SUSPPUP

SUSPUP (serum sodium to urinary sodium to serum potassium to urinary potassium) and SUSPPUP (serum sodium to urinary sodium to (serum potassium)² to urinary potassium) are calculated structure parameters of the renin–angiotensin-aldosterone system (RAAS). They have been developed to support screening for primary or secondary aldosteronism.^[1][2]

The steroid hormone aldosterone stimulates the reabsorption of sodium and the excretion of potassium in the distal tubuli and the collecting tubes of the kidneys. Calculating SUSPUP and/or SUSPPUP helps to determine the intensity of mineralocorticoid signalling, which may be helpful in the differential diagnosis of hypertension and hypokalaemia.^{[citation needed]}

Sodium and potassium concentrations have to be determined in serum and spot urine probes that have been obtained simultaneously or within a short time interval between.^{[citation needed]}

${\displaystyle SUSPUP={\frac {\frac {{[Na}^{+}]_{Serum}}{{[Na}^{+}]_{Urine}}}{\frac {{[K}^{+}]_{Serum}}{{[Na}^{+}]_{Urine}}}}}$

${\displaystyle SUSPPUP={\frac {\frac {{[Na}^{+}]_{Serum}}{{[Na}^{+}]_{Urine}}}{\frac {{[K}^{+}]_{Serum}^{2}}{{[Na}^{+}]_{Urine}}}}}$

Reference ranges are 3.6–22.6 for SUSPUP and 0.6–5.3 for SUSPPUP.^[1]

Increased values support the hypothesis of increased mineralocorticoid stimulation of the distal tubules and collecting tubes, i.e. in cases of hyperaldosteronism.^[3] While these parameters have a high sensitivity for screening purposes their specificity may be inferior compared to aldosteron-to-renin ratio (ARR) and potassium concentrations^[4]

Both parameters may also be elevated in syndrome of inappropriate ADH secretion (SIADH), probably reflecting a compensatory mechanism, where the organism tries to maintain serum sodium concentrations by means of increased renin and/or aldosterone secretion.^[5]