ECM/BCM
ECM/BCM Ratio
The ECM/BCM ratio compares extracellular mass with body cell mass and serves as a supplementary indicator of nutritional status.
Short answer
ECM/BCM is a ratio indicator from the research section of the result. On its own it establishes the cause of nothing — use it only as a companion to body cell mass and to the ECW Ratio.
What the value represents
In this model the body divides into two parts: what is inside the cells and what is outside them.
Body cell mass (BCM) is, per the manual, the sum of intracellular water and protein. Extracellular mass (ECM) is the remainder of fat free mass, that is fat free mass minus body cell mass — chiefly extracellular water and bone minerals.
The ratio says how much extracellular mass falls to a unit of cell mass. A higher number means a relatively larger extracellular component, or a smaller cellular one. The number alone does not tell you which.
It is a research parameter, not a headline value. The manual lists it among supplementary parameters and describes it as an indicator for nutritional assessment.
- The ratio of extracellular mass to body cell mass, dimensionless.
- A supplementary indicator of nutritional status closely related to the ECW Ratio.
- It does not represent oedema, inflammation, malnutrition or any other health state.
How the value is produced
- A calculated value. The manual gives: extracellular mass = fat free mass − body cell mass; body cell mass = intracellular water + protein.
- Intracellular water is derived from measured impedance, protein is calculated, and fat free mass arises as the sum of water, protein and minerals. The ratio therefore rests on several successive estimates.
- On the Evaluation Result Sheet the value is compared against the manufacturer reference set through Z- and T-scores, according to the catalogue.
How to read the current value
- The manual gives neither a reference range nor a threshold for this ratio. The result sheet shows the number itself, and possibly Z- and T-scores.
- Read it as a companion to the ECW Ratio. Both describe a similar thing from different angles.
- A higher ratio can arise by two routes: a larger extracellular component, or a lower cell mass. The number does not establish which.
- The manual recommends body cell mass as a nutritional indicator in older adults and people with fluid retention, because BMI and fat free mass can be distorted there by excess extracellular water.
How to read change over time
- Follow the ratio alongside body cell mass in kilograms. Only then do you know whether the numerator, the denominator or both moved.
- Short-term swings correspond to variation in hydration; the whole calculation rests on an estimate of body water.
- For tracking, an interval of months and comparable measurement conditions make sense, not a comparison of two visits in one week.
General principles: how to read change between measurements →
What to read it with
- Body Cell Mass (BCM) – the denominator of the ratio.
- The ECW Ratio – the water-based analogue of the same view.
- Extracellular and intracellular water – the components both are derived from.
- Protein – the other component of body cell mass.
- Fat free mass – the whole that extracellular mass is subtracted from.
Common misunderstandings
- The ratio does not confirm oedema. A raised value is a prompt to look at context, not a diagnosis.
- It is not an indicator of dietary protein intake. For protein the manual explicitly warns that a deficiency on the result sheet means the amount of protein in muscle tissue, not eating habits.
- A lower value is not automatically better; it is a ratio of two estimates.
- The Z- and T-scores next to the value are comparisons against the manufacturer data set, not clinical norms.
What can affect the result short term
- Hydration and fluid intake, because the ratio rests on estimates of body water.
- Training, sauna and showering shortly before the measurement.
- Time of day and the shift of fluid towards the lower half of the body.
- The menstrual cycle.
- Illness, fever and states accompanied by fluid retention.
What to do next
- Treat the value as supplementary. For ordinary tracking of body composition, muscle mass, fat and the ECW Ratio are enough.
- If nutritional status interests you, follow body cell mass in kilograms above all; the manual recommends it as a more suitable indicator than BMI or fat free mass in people with fluid retention.
- When the ratio shifts over time and is accompanied by swelling, weight loss or fatigue, that belongs with a doctor.
What the value does not determine
- It does not diagnose oedema, malnutrition or inflammation.
- It does not establish the cause of a change, because it moves from both sides of the fraction.
- It shares the uncertainty of the body water and protein estimates.
- The manual gives no reference range for it.
On terminology
- ECM stands for Extracellular Mass, that is fat free mass minus body cell mass. Do not confuse it with extracellular water (ECW), which is only part of it.
When to discuss it with a professional
If swelling, unintended weight loss or persistent fatigue is what brought you to this value, that belongs with a doctor. A bioimpedance ratio is supplementary information, not an examination.
In more depth, with sourcesIn more depth: what the ratio aggregates and why a cause cannot be read from itExpand the detailed explanation
Written out, the ratio is (fat free mass − body cell mass) ÷ body cell mass, where body cell mass is the sum of intracellular water and protein. Intracellular and extracellular water both come from the same impedance measurement, so errors in the numerator and denominator are not independent. A shift in the estimated distribution of water therefore moves the value from both sides of the fraction at once, and the result cannot simply be decomposed back into a cause.
The manual gives the ratio as an indicator for nutritional assessment and at the same time recommends body cell mass as the more suitable indicator in older adults and in people with oedema, fluid retention or ascites, where BMI and fat free mass can be distorted by raised extracellular water. The ESPEN clinical guidelines on bioimpedance point to the same thing from the other side: where fluid distribution is altered, body composition estimates are less reliable. These are therefore the situations in which the ratio changes most and is at the same time hardest to interpret.
The Z- and T-scores on the evaluation sheet express position relative to the manufacturer reference set rather than to clinical norms, and must not be confused with identically named scores from other fields, such as bone density assessment. The NIH consensus statement on bioimpedance further recalls that comparability of repeated measurements stands or falls with standardised conditions.
Sources
- InBody 970 Result Sheet Interpretation (ENG_A_211104) — InBody Co., Ltd.
- Bioelectrical impedance analysis – part II: utilization in clinical practice — Clinical Nutrition (ESPEN guidelines)
- Bioelectrical impedance analysis in body composition measurement: NIH Technology Assessment Conference Statement — National Institutes of Health
On this page
Related values
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Where to find it
The Visceral Fat Analysis, circumferences and basal metabolic rate.
- Reviewed by
- MojeInBody content team
- Date
An InBody measurement is not a diagnostic tool. Results do not determine health status and do not replace a medical examination.
FAQ
Frequently asked questions
Answers to what people ask most often about this value.
Does a higher ECM/BCM mean I have oedema?
No. A higher value can arise from a larger extracellular component or from a smaller cell mass, and the ratio alone does not reveal which. Oedema is a clinical finding the device does not establish.
What value is fine?
The manual gives no reference range for this ratio. The evaluation sheet shows only Z- and T-scores against the manufacturer data set, which is not a clinical norm.
How does it differ from the ECW Ratio?
The ECW Ratio works with water alone: how much of total water sits outside the cells. ECM/BCM additionally includes protein on the cell mass side and bone minerals on the extracellular side. They therefore describe a similar thing but are not interchangeable.
Explanations make the most sense alongside your own trend.
The public guide is open to everyone. The client portal adds your own value, history and the context of a specific measurement.