Renal and Genitourinary Core

The kidneys regulate extracellular volume, potassium and other electrolytes, acid–base balance, erythropoietin production, vitamin D activation and removal of metabolic waste. A renal problem therefore presents as more than an abnormal creatinine: it can alter blood pressure, medication exposure, mental status, cardiac conduction, bone health and fluid distribution. A useful clinical pattern is to separate loss of filtration, loss of concentrating or tubular function, and urinary flow obstruction. Reduced filtration raises creatinine and potassium and may produce acidosis or uraemic symptoms. Tubular dysfunction can disturb fluid, electrolyte or acid handling even before creatinine becomes strikingly abnormal. Obstruction may first appear as pain, retention, hydronephrosis or falling urine output. The same patient can have more than one process—for example, an older adult with CKD who becomes volume depleted while taking an NSAID and an ACE inhibitor. The experienced nurse looks at trends and context rather than one isolated value. A small creatinine rise may represent a major fall in filtration in a patient with little muscle mass, while a “normal” creatinine can conceal impaired kidney function in frailty. Falling urine output,...