Proteinuria: diagnostic approach

The single idea that organises the whole topic is that most childhood proteinuria is benign, but a minority signals kidney disease, and the job of the general paediatrician is to confirm before classifying and to classify before treating. A protein trace on a dipstick taken during a fever is almost always meaningless, an adolescent with proteinuria only when upright has orthostatic proteinuria, and a child with heavy proteinuria and oedema has nephrotic syndrome. The diagnostic pathway exists to sort these three quickly and safely, and to avoid both the harm of missing disease and the harm of over-investigating a healthy child. ^{[2] [6]}

This page covers the definition and the exact paediatric thresholds, the classification into transient, orthostatic and persistent patterns, the physiology of why protein leaks, the focused history and examination, the quantification tests with their pitfalls, and the stepwise pathway from a dipstick to a nephrology referral. It links to the oedema and nephrotic syndrome leaf for nephrotic-range disease, to the acute nephritic syndrome and glomerulonephritis leaf for proteinuria with haematuria, and to the urinalysis and renal function leaf for the laboratory methods, rather than duplicating them. ^{[1] [5]}

Overview & Definition

Proteinuria means that the urine carries more protein than the healthy kidney should allow through. The kidney normally filters a tiny amount of protein and reabsorbs almost all of it, so the daily loss is small. The standard paediatric definition of proteinuria is a urinary protein excretion of 100 mg per square metre per day or more on a timed collection (the pathological cut-off in a large paediatric correlation study), or a spot first-morning urine protein-to-creatinine ratio above the age-specific normal.^[11] The KDIGO 2024 guideline carries these definitions into contemporary practice alongside the albuminuria categories that stratify kidney-disease risk. ^{[1] [2]}

What matters clinically is that a single dipstick reading is not proteinuria. A child who has protein on a dipstick taken during a fever, after exercise, or simply while standing has not been diagnosed, because these are the common benign reasons for transient and postural protein that vanish on a repeat sample. Proteinuria is only declared when the finding persists on repeat testing, and it is only pathological when it persists in the recumbent, first-morning sample. This distinction is the whole point of the workup, and it is the step most often skipped. ^{[2] [6]}

The reason the definition carries weight is that it decides what happens next. A child whose proteinuria resolves on repeat needs nothing further, a child with orthostatic proteinuria needs monitoring, and a child with persistent pathological proteinuria needs quantification, a secondary panel, and a nephrology opinion. Holding the thresholds and the repeat-sample discipline is what keeps the workup both thorough and proportionate. ^{[1] [3]}

References13ShowHide

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