Definitions & Reference
Understand the metrics and clinical reasoning.
How a period is measured
A period runs from one first morning void to the next: Day 1 is (morning-1 first void, morning-2 first void]. The opening void is excluded, the closing void is included. Three measured periods therefore need four mornings, which is why the diary records the morning after Day 3.
Night N is the window from the bedtime inside period N to the first morning void that closes it. NPi is that nocturnal volume over the same period’s own 24HV, not over a calendar day.
The first void of Day 1 is the previous, unrecorded night’s production. It is shown in the diary and marked "Diary start (not counted)", but it is added to no period total and it cannot set MVV.
Diaries uploaded from myflowcheck.com are computed with exactly this method, so the numbers here and the numbers on the patient’s own report describe the same days under the same labels.
Every windowed metric is a measurement or nothing. When a boundary first morning void was never recorded, the period reports "-" and names the missing morning. It is never reported as zero, and a missing middle morning never widens a period to 48 hours.
Key Metrics
Total urine volume passed in one period, day plus night: every void from one first morning void (exclusive) to the next (inclusive).
Percentage of a period’s urine output produced at night. Numerator: the volume from that period’s bedtime to the first morning void that closes it, including that void. Denominator: the same period’s 24HV.
Largest single voided volume recorded in the diary. Excludes the Day 1 diary-start void, which is the previous unrecorded night’s accumulation and would otherwise set the maximum in most diaries.
Average volume per void over a period. Each pass of a double void counts as its own void.
Amount left in the bladder after voiding, measured externally by ultrasound or catheter. Not derived from diary data.
Whether any leakage occurred during the diary period.
The 4Is Classification
The total amount or timing of urine output looks off. May indicate too little fluid intake, too much, or abnormal nighttime production.
The bladder may be storing too little (capacity impairment) or signaling too early (sensory impairment). Assessed by comparing MVV and AVV.
The bladder may not be emptying well. Assessed by PVR measurement. If PVR > 100 mL, voiding impairment is suspected.
Leaking is present. Determined by any reported leakage episodes or nocturnal enuresis.
Clinical Thresholds
| Metric | Low/Abnormal | Normal | High/Abnormal |
|---|---|---|---|
| 24HV | < 1,000 mL (34 oz)/day (oliguria) | 1,000: 2,500 mL (34: 85 oz)/day | > 2,500 mL (85 oz)/day (polyuria) |
| NPi | - | ≤ 20% (younger) / ≤ 33% (age ≥ 65) | > threshold = nocturnal polyuria |
| MVV | < 150 mL (5 oz) (small) | 150: 350 mL (5: 12 oz) | > 350 mL (12 oz) (large) |
| PVR | - | < 100 mL (3.4 oz) | > 100 mL (3.4 oz) (impaired emptying) |
| AVV/MVV | < 60% (sensory pattern) | 60: 70% | - |
About IPC
IPC provides continuing education to health professionals to raise standards in male pelvic health treatments. To deepen your understanding of bladder diary analysis, functional diagnosis, visit ipc.health.