What if I don't need to urinate at the end of my 24-hour (twenty-four hour) urine volume collection?

What to Do If You Don't Need to Urinate at the End of Your 24-Hour Urine Collection

If you don't need to urinate at the end of your 24-hour collection period, you should still attempt to void even if only a small amount comes out, or wait up to 30-60 minutes past the scheduled end time to complete the final void—the collection is only valid if it includes that final bladder emptying, as an incomplete collection will underestimate your true urine volume and all measured analytes. 1, 2

Why the Final Void Is Critical

The 24-hour urine collection protocol specifically requires that you:

• Empty and discard your bladder at the start time (this urine is NOT collected) 1, 2
• Collect every single void during the 24-hour period 1, 2
• Include the final void at exactly 24 hours later, even if you don't feel a strong urge 1, 2

Missing the final void means your collection is incomplete and will produce falsely low results for urine volume, creatinine excretion, and all other measured substances. 1, 3 This can lead to misdiagnosis or inappropriate treatment decisions, particularly for conditions like kidney stones where urine volume is a critical therapeutic target. 4, 5

Practical Steps If You Don't Feel the Urge

Immediate Actions

• Wait 30-60 minutes past your scheduled end time while drinking a normal amount of water (not excessive) to allow your bladder to fill enough for a final void 6
• Attempt to urinate anyway, even if you produce only a small amount—every drop counts and should be added to your collection container 1, 2
• Do not force excessive fluid intake in the final hours just to produce urine, as this artificially dilutes your sample and defeats the purpose of measuring your natural urine concentration 7

If You Absolutely Cannot Void

If after waiting 60 minutes you still cannot produce any urine:

• Contact the ordering physician or laboratory immediately to report the incomplete collection 1, 8
• You will likely need to repeat the entire 24-hour collection, as an incomplete sample cannot be accurately interpreted 3, 5
• Document the exact time of your last collected void so the laboratory knows the actual collection duration 1

Common Pitfalls and How to Avoid Them

Bladder Dwell Time Matters

First morning urine after overnight bladder dwell time is more concentrated and contains higher bacterial counts and cellular elements than random voids. 6 If your collection ends in the morning and you haven't voided overnight, that final morning void is particularly important because:

• It represents 6-8 hours of urine production 6
• Missing it could underestimate your total volume by 25-40% 6, 4
• Bacterial counts and other analytes will be falsely low if this concentrated specimen is excluded 6

Gender Differences in Collection Adequacy

Women are nearly 50% less likely to provide adequate 24-hour urine samples compared to men, with inadequate collections occurring in over 50% of female patients in some studies. 3 This may relate to:

• Difficulty with complete collection technique 3
• Lower average urine volumes in women 4
• Greater likelihood of discarding voids accidentally 8, 3

If you are female, pay extra attention to collecting every single void, including the final one, as you are at higher risk for incomplete collection. 3

Creatinine Excretion as a Quality Check

Laboratories use 24-hour creatinine excretion to verify collection completeness:

• Expected creatinine excretion is 15-25 mg/kg/day for men and 10-20 mg/kg/day for women 1, 3
• Collections with creatinine values outside these ranges are flagged as potentially incomplete 1, 3
• Missing the final void will result in low creatinine excretion, triggering rejection of your sample 3, 5

Special Circumstances

Low Urine Volume Patients

If you naturally produce low urine volumes (less than 2 liters per 24 hours), you may void infrequently—perhaps only 3-4 times daily. 1, 4 In this case:

• You may need to extend your collection to 48 hours to capture at least 3 complete bladder voidings 2
• The final void becomes even more critical as it may represent 6-8 hours of production 6
• Consider setting an alarm at the 24-hour mark to remind yourself to attempt the final void 8

Patients with Diabetes Insipidus or Polyuria

If you have conditions causing excessive urine production (polyuria), you likely void frequently and the final void is less problematic. 7 However:

• Still attempt the final void at exactly 24 hours to maintain accurate timing 1, 2
• Your collection may total 4-6 liters or more, making completeness verification easier 7

Why Repeat Collections May Be Necessary

Even with a complete collection including the final void, up to 25% of children and a significant proportion of adults show discordant results between consecutive 24-hour collections, particularly for urine oxalate, calcium, and supersaturation ratios. 9 This means:

• Your physician may order a second 24-hour collection to confirm abnormal findings 5, 9
• Both collections must include the final void to be valid 1, 2
• Variability between collections is normal and doesn't necessarily indicate collection error 5, 9

The key message: Never skip the final void. If you cannot produce it within 60 minutes of the scheduled end time, contact your healthcare provider immediately, as the collection will need to be repeated. 1, 2, 3