A Very Low-Function Kidney (<20%): Pyeloplasty or Nephrectomy?

The EAU/ESPU guideline defines a kidney with split function under 20% as "low-function." This means the kidney is carrying less than a fifth of total function; the opposite kidney is carrying the bulk of the load.

This is families' most common question, and the answer depends on age. In the literature, a meaningful increase in function after pyeloplasty is generally not expected in a kidney with very low function; if the kidney tissue has been under prolonged pressure, the loss is permanent.

In a low-function kidney there are three paths: primary pyeloplasty, nephrectomy, or follow-up. The guideline does not give a clear order among the three; the decision is made by weighing the following criteria together.

• Age: because of the chance of partial recovery in infancy, repair weighs heavier; in an older child this chance is small.
• Symptoms: a low-function kidney causing recurrent pain or febrile infection calls for intervention rather than follow-up.
• Degree of swelling and parenchyma: a very thin kidney with almost no tissue left gains little from repair.
• Status of the opposite kidney: if the opposite kidney is healthy, nephrectomy is discussed more readily; if the opposite kidney also has problems, or there is only one kidney, every bit of tissue is preserved if possible.
• The family's preference: when both approaches are defensible, a family discussion is part of the decision.

The commonly cited threshold for nephrectomy is function under 10%; some centers use 15% as the cutoff. However, no firmly established threshold exists in the guideline, and this decision is for "highly selected" cases. A significant portion of kidneys with function between 10–20% are preserved.

In a child with a solitary kidney, or with bilateral hydronephrosis, the concept of a "low-function kidney" changes meaning: since split function is a share, it cannot be calculated for a solitary kidney, and in a bilateral picture, a kidney that looks low may be a critical part of total function. In these children, nephrectomy is almost never on the table; the goal is always to preserve.

• While a low-function kidney is being followed or drained with a nephrostomy, present without waiting for the scheduled visit in the following situations: fever (38°C/100.4°F or above) with flank pain; fever, bleeding, or the nephrostomy drainage stopping while a nephrostomy is in place; decreased urine output, swelling, or fatigue in a solitary kidney or a bilateral picture.