Nutritional Risk Index (NRI): how the albumin and weight formula works

The Nutritional Risk Index (NRI) is 1.519 × serum albumin in g/L plus 41.7 × current weight divided by usual weight. Albumin 40 g/L with no weight change gives an NRI of 102.5, which is above 100 and labeled not_malnourished.

Not a medical device. Not a diagnosis or dosing recommendation.

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The Veterans Affairs Total Parenteral Nutrition Cooperative Study Group · 1991
The NRI formula
Worked examples
Frequently asked questions

What is the Nutritional Risk Index?

The NRI comes from the Veterans Affairs Total Parenteral Nutrition (VA TPN) Cooperative Study Group, published in the New England Journal of Medicine in 1991. It combines a blood protein (albumin) with recent weight change into one number. Lower values point to greater nutritional risk.

Magent's calculator returns the NRI to 1 decimal place, a two-way screening label (100 or below is malnourished) and a four-way stratification label using the bands from the 1991 paper.

This page explains the arithmetic and the labels. It doesn't say what a value means for a particular person.

The NRI formula

NRI = 1.519 × albumin (g/L) + 41.7 × (current weight ÷ usual weight)
rounded to 1 decimal

screening:       malnourished if NRI ≤ 100 · not_malnourished if NRI > 100
stratification:  not_malnourished        NRI > 100
                 borderline_malnourished 97.5 < NRI ≤ 100
                 mildly_malnourished     83.5 ≤ NRI ≤ 97.5
                 severely_malnourished   NRI < 83.5

Exact expression the calculator uses:

NRI = 1.519 × albumin_g_l + 0.417 × (current_weight_kg / usual_weight_kg) × 100

The record writes the weight term as 0.417 × (ratio) × 100, which is the same as 41.7 × (ratio).

Inputs

Input	Meaning	Accepted range
`albumin_g_l`	Serum albumin, g/L	10 to 60
`albumin_g_dl`	Or serum albumin in g/dL; multiplied by 10	1 to 6
`current_weight_kg`	Current weight, kg	1 to 500
`usual_weight_kg`	Usual weight, kg	1 to 500

How the calculation works

Albumin term: multiply albumin in g/L by 1.519.
Weight term: divide current weight by usual weight and multiply by 41.7. With no weight change the ratio is 1 and this term is 41.7.
Add the two terms and round to 1 decimal.
Screening label: 100 or below is malnourished; above 100 is not_malnourished.
Stratification label: above 100 not_malnourished; above 97.5 up to 100 borderline_malnourished; 83.5 up to 97.5 mildly_malnourished; below 83.5 severely_malnourished.

Both labels are set from the rounded NRI. Current weight isn't capped at usual weight, so weight gain raises the weight term above 41.7.

Units

The formula uses albumin in g/L. If you have g/dL, use the g/dL input and the calculator multiplies by 10 (4.0 g/dL becomes 40 g/L). Give one albumin input, not both. Weights are in kg; because the formula uses their ratio, the two weights must be in the same unit. A missing value or one outside its range is rejected with an error.

Worked examples

These use Magent's own expected values for the calculator. In each, current and usual weight are both 70 kg, so the weight term is 41.7.

Example 1: albumin 40 g/L

1.519 × 40 = 60.76.
60.76 + 41.7 = 102.46 → 102.5.
Above 100 → screening not_malnourished, stratification not_malnourished.

Example 2: albumin 38.38 g/L

The sum rounds to 100.0.
100 or below → screening malnourished; above 97.5 up to 100 → borderline_malnourished.

Example 3: albumin 36.73 g/L

The sum rounds to 97.5.
Screening malnourished; 97.5 sits in the 83.5 to 97.5 band → mildly_malnourished.

Example 4: albumin 27.52 g/L

The sum rounds to 83.5.
83.5 is the bottom edge of the mild band → mildly_malnourished.

Example 5: albumin 25 g/L

The sum rounds to 79.7.
Below 83.5 → severely_malnourished.

Example 6: albumin given as 4.0 g/dL

4.0 × 10 = 40 g/L.
Same result as Example 1: 102.5, not_malnourished.

History of the Nutritional Risk Index

The calculator cites the Veterans Affairs Total Parenteral Nutrition Cooperative Study Group, Perioperative total parenteral nutrition in surgical patients, New England Journal of Medicine, 1991 (volume 325, issue 8, pages 525–532). The abstract describes a randomized study of perioperative total parenteral nutrition in malnourished patients having laparotomy or noncardiac thoracotomy. Patients were grouped as borderline, mildly or severely malnourished by Subjective Global Assessment or an objective nutritional assessment. The NRI formula and its bands, as used here, come from that paper.

When it's used

The 1991 study applied the NRI to adults before major abdominal or chest surgery to grade nutritional status.

Where it's used

The NRI needs a serum albumin result and two weights: current and usual. No other measurements go into it.

Who uses it

The person using the calculator enters albumin and the two weights. The calculator works out the NRI and assigns both labels.

Limits of the calculation

The calculator doesn't measure albumin or weigh anyone. Usual weight comes from the person entering it.
The labels follow the 1991 bands. Later sources that split the bands differently aren't applied.
It's the 1991 NRI. It isn't the geriatric NRI (GNRI) or the prognostic nutritional index (PNI).
It isn't an order to start parenteral nutrition.
This page doesn't say what to do with a value.

Clinical decisions belong to a qualified clinician who knows the patient.

Nutritional Risk Screening (NRS) adds graded nutritional status and disease severity categories plus an age point, with no lab value.
MUST uses BMI, unplanned weight loss and acute illness effect.

Glossary

Serum albumin: a blood protein, entered in g/L or g/dL.
Usual weight: the person's weight before the current illness.
Weight ratio: current weight divided by usual weight.
TPN: total parenteral nutrition, feeding by vein, the subject of the 1991 study.

Common mistakes

Entering albumin in g/dL as g/L. 4.0 g/dL is 40 g/L. Use the g/dL input or convert first.
Capping the weight ratio at 1. The calculator doesn't cap it.
Mixing weight units. Current and usual weight must be in the same unit.
Confusing NRI with NRS. They're different tools.

Source

Veterans Affairs Total Parenteral Nutrition Cooperative Study Group. Perioperative total parenteral nutrition in surgical patients. N Engl J Med. 1991;325(8):525-532. DOI: 10.1056/NEJM199108223250801. PMID: 1906987

Frequently asked questions

How do you calculate the Nutritional Risk Index?

Multiply albumin in g/L by 1.519, then add 41.7 × current weight divided by usual weight.

What NRI value is labeled malnourished?

100 or below. Above 97.5 up to 100 is borderline, 83.5 to 97.5 is mild and below 83.5 is severe.

What is the difference between NRI and Nutritional Risk Screening (NRS)?

NRI is a formula from albumin and weight change. NRS adds graded categories and an age point.

Can I enter albumin in g/dL?

Yes. The calculator multiplies by 10 to get g/L.

Does weight gain change the NRI?

Yes. The ratio isn't capped, so a current weight above usual weight raises the NRI.