“Interval increase” most commonly appears in medical imaging reports, where it means a finding has grown larger since the last scan. The word “interval” refers to the time between two imaging studies, and “increase” means the size, volume, or extent of something (a nodule, fluid collection, or swelling) has gotten bigger during that window. The phrase can also show up in fitness programming and pay structures, where it carries different but related meanings.
Interval Increase on a Radiology Report
When a radiologist reads your CT, MRI, or X-ray, they compare the new images to your previous ones. Any change they note between those two time points is called an “interval change.” That change can go in three directions: improvement (something shrank or resolved), stability (no meaningful difference), or worsening. An “interval increase” falls into the worsening category. It tells your doctor that something measurable, like the diameter of a lung nodule or the amount of fluid around the brain, has grown since the prior study.
The phrasing is deliberately precise. Radiologists use “interval increase” rather than vague terms like “bigger” because it anchors the observation to a specific comparison point. If your report says “interval increase in the size of the right lower lobe nodule,” it means the radiologist looked at both scans side by side and confirmed the nodule is larger now than it was on the earlier image.
When Interval Increase Matters Most
Not every interval increase is alarming. A small amount of post-surgical swelling that grows slightly over a few days, for example, can be expected. Context determines whether the change is routine or concerning. Two of the most common scenarios where interval increase triggers further action are lung nodule monitoring and cancer treatment tracking.
Lung Nodules
Lung nodules are small spots found on chest CTs, and the vast majority are benign. Doctors monitor them with follow-up scans at set intervals, typically at 3 to 6 months, 9 to 12 months, and 18 to 24 months for solid nodules larger than 8 mm. The key question is whether the nodule grows. Malignant nodules typically double in volume within about 400 days. Because nodules are roughly spherical, a volume doubling translates to only about a 26% increase in diameter, a change that can be subtle on imaging but clinically significant.
For ground-glass nodules (hazy spots that don’t fully block the lung tissue behind them), any growth or development of a solid component is a red flag that often leads to biopsy or surgical removal. Part-solid nodules follow a similar rule: if they grow or develop a denser core over serial scans, further evaluation is warranted. So when your report notes an “interval increase” in a nodule’s size, it’s the finding that moves the monitoring process to the next step.
Cancer Treatment Response
In oncology, interval increase has a formal threshold. The standard measurement system used worldwide defines progressive disease as at least a 20% increase in the combined diameters of target tumors, plus an absolute growth of at least 5 mm. If tumors meet that bar between scans, or if new lesions appear, the cancer is classified as progressing. This threshold helps oncologists decide whether a treatment is working or whether a change in approach is needed.
What to Do if Your Report Says It
If you’re reading your own radiology report and see “interval increase,” the most important thing to understand is that the phrase describes a measurement, not a diagnosis. It tells you something got bigger. Whether that matters depends on what grew, by how much, and over what timeframe. A 1 mm change in a small nodule over six months may fall within measurement error. A 26% diameter jump in a solid lung nodule over a year is a different story.
Your ordering physician will interpret the finding in the context of your full medical history, the radiologist’s overall impression (usually at the bottom of the report), and any recommended follow-up. If the radiologist considers the increase significant, they’ll typically recommend a shorter follow-up interval, a different type of scan, or a biopsy.
Interval Increase in Fitness Training
Outside medicine, “interval increase” often refers to making interval workouts progressively harder. In high-intensity interval training (HIIT), there are several ways to do this: lengthening the work periods, shortening the rest periods, raising the intensity, or adding more rounds. One structured protocol for adults with type 2 diabetes, for example, increased the high-intensity work duration by 7% to 10% and decreased recovery time by 4% every two weeks, while adding two extra intervals every four weeks. Another approach simply extends sprint durations over time, starting at 10 seconds per sprint and building to 20 seconds across several weeks.
The reason for gradually increasing interval difficulty is the same principle behind progressive overload in strength training. Higher-intensity exercise triggers greater improvements in aerobic capacity and drives more mitochondrial growth in muscle cells compared to the same total volume of work performed at lower intensity. Interval training generally improves VO2 max (your body’s ceiling for oxygen use during exercise) more effectively than steady-state cardio when training volume is matched.
Interval Increase in Pay Structures
In government and some corporate settings, “interval increase” describes scheduled pay raises tied to time in a position. The U.S. federal pay system is a clear example. Each General Schedule (GS) grade has 10 steps, and employees move up one step at a time based on set waiting periods. Steps 1 through 4 each require one year (52 weeks) of service. Steps 4 through 7 each require two years (104 weeks). Steps 7 through 10 each require three years (156 weeks). To qualify, an employee needs at least a “Fully Successful” performance rating.
These step increases are sometimes called within-grade increases, and they function as automatic raises for employees who meet the time and performance requirements. The slowing pace of advancement (from annual to biennial to triennial) means early-career employees see more frequent bumps, while later increases reward sustained tenure.