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A 24-hour urine collection is a timed specimen used for evaluating urinary stone disease, proteinuria (eg, amyloidosis, lupus nephritis, nephrotic syndrome, and preeclampsia), multiple myeloma, pheochromocytoma (fractionated metanephrines and catecholamines), and renal function through urea and creatinine clearance. This test is usually conducted in an outpatient setting while the patient maintains their usual diet. Results are analyzed alongside detailed medical and dietary history, serum chemistry, and stone composition (if available) to assist in diagnosis and guide therapy or prophylactic treatment. Further, this urine study can be used in pediatrics to test for inherited conditions such as primary hyperoxaluria and cystinuria.[1][2] Pheochromocytomas and paragangliomas, which are rare conditions causing catecholamine excess, are diagnosed in symptomatic individuals through elevated urine and plasma metanephrines. The collection procedure is similar to other conditions; however, the data must be interpreted cautiously due to the very low pretest probability.[3] Current laboratory values estimate the glomerular filtration rate (GFR) based on creatinine levels. However, these estimates can vary significantly from the true GFR if creatinine levels are unstable or for other reasons. Therefore, a 24-hour urine collection can be a valuable tool in evaluating abnormal renal function, but adherence to proper collection techniques is essential, as is educating the patient about the strict guidelines for a 24-hour collection. Shorter urine collections, such as 8- or 12-hour, can improve patient adherence and accuracy in specimen collection. However, 24-hour collections are generally preferred because they account for daily creatinine variations and solute excretion.

Catecholamines are rapidly inactivated by the catechol-O-methyltransferase, converting them into metanephrine and normetanephrine, which are then conjugated with sulfate. These compounds have a long half-life and are excreted in the urine, making them more suitable for measurement than catecholamines. Elevated plasma metanephrines are considered more specific than elevated urine metanephrines. Additionally, the level of increased metanephrine correlates with tumor size. Please see StatPearls' companion resources, "Renal Calculi, Nephrolithiasis" and "Chronic Kidney Disease," for details on the pathophysiology of nephrolithiasis and CKD. The European Society of Clinical Practice Guidelines recommend using liquid chromatography with mass spectrometry or electrochemical detection methods over other techniques. Literature reports that urine metanephrines' sensitivity ranges from 86% to 97%, while specificity ranges from 69% to 95%.[7] A key consideration is that, due to the frequent testing and the low prevalence of true pheochromocytoma and paraganglioma, false positives significantly outnumber true positives.[8][9] Please see StatPearls' companion resource, "Pheochromocytoma," for more information.

A 24-hour urinalysis is a timed urine collection used to evaluate the metabolic status of various kidney disorders and accurately quantify GFR and proteinuria. For inpatients, nurses typically collect the urine and must ensure it remains free from contaminants. In outpatient settings, patients need proper education on how to collect the urine sample accurately. Precise collections can identify treatable abnormalities that predispose to nephrolithiasis, assist in diagnosing conditions such as pheochromocytoma, and provide accurate measurements for monitoring the progression of CKD. Effective communication among healthcare team members is paramount. Primary care clinicians and hospitalists often identify renal abnormalities first and may refer patients to pediatric or adult nephrologists. Patients with significant nephrolithiasis should be offered 24-hour urine testing for stone prophylaxis therapy and should be referred to urology. Clinicians and nurses must ensure that patients are fully informed about the procedures and requirements for 24-hour urine collection, with clear, written instructions provided to support patient understanding. Laboratory staff should ensure proper specimen handling and processing. Clear communication across the healthcare team facilitates timely diagnosis and treatment decisions, enabling a coordinated response and the effective use of clinical data.