Hypophosphataemia & Refeeding Syndrome Risk Interpreter
Hypophosphataemia & Refeeding Syndrome Risk Interpreter
Grade a low phosphate, then apply the NICE CG32 refeeding-risk criteria exactly as published — one of four major criteria, or two of four minor ones — and see how the 2020 ASPEN consensus criteria differ. Add the TmP/GFR result to decide whether phosphate is being lost through the kidney or has moved into cells.
Low phosphate: how severe, and is this refeeding?
Phosphate + NICE CG32 criteria → severity and refeeding riskA 58-year-old man with alcohol misuse admitted after a fall. BMI 17.2, 12% weight loss over 4 months, eating very little for a week. Phosphate before feeding 0.42 mmol/L; potassium and magnesium normal.
NICE CG32, recommendation 1.4.6 — high risk of refeeding problems
OR TWO OR MORE of: BMI below 18.5 kg/m² · unintentional weight loss above 10% within 3–6 months · little or no intake for more than 5 days · a history of alcohol abuse or drugs including insulin, chemotherapy, antacids or diuretics
Phosphate (Merck): mild 0.65–0.81, moderate 0.32–0.65, severe below 0.32 mmol/L
- counts
- the page prints how many criteria from each list are met, so the reader can see why
- low before feeding
- counted when this phosphate was taken before feeding and is below 0.81 mmol/L (2.5 mg/dL), or when potassium or magnesium was low before feeding
- mmol/L to mg/dL
- × 3.0974 (phosphorus 30.974 g/mol); each unit is tested against its own published figure
Worked example
A 58-year-old man with alcohol misuse admitted after a fall. BMI 17.2, 12% weight loss over 4 months, eating very little for a week. Phosphate before feeding 0.42 mmol/L; potassium and magnesium normal.
Phosphate 0.42 mmol/L → moderate (0.32 to 0.65)
One-or-more list: low phosphate before feeding → 1 met
Two-or-more list: BMI below 18.5, weight loss above 10%, intake low above 5 days, alcohol → 4 met
Either list alone makes him high risk: start at no more than 10 kcal/kg/day, with thiamin and electrolytes
NICE CG32 and ASPEN 2020 compared
| Criterion | NICE CG32 (1.4.6) | ASPEN 2020 — moderate risk (2 needed) | ASPEN 2020 — significant risk (1 needed) |
|---|---|---|---|
| BMI | Below 16 (major) · below 18.5 (minor) | 16 to 18.5 | Below 16 |
| Weight loss | Above 15% in 3–6 months (major) · above 10% (minor) | 5% in 1 month | 7.5% in 3 months, or above 10% in 6 months |
| Intake | Little or none above 10 days (major) · above 5 days (minor) | None or negligible 5–6 days; or below 75% of need for above 7 days in acute illness, or above 1 month | None or negligible above 7 days; or below 50% of need for above 5 days in acute illness, or above 1 month |
| Potassium, phosphate, magnesium before feeding | Low (major) | Minimally low, or normal but recently needing minimal or single-dose supplements | Moderately or significantly low, or recently needing significant or repeated supplements |
| Alcohol and drugs | Alcohol abuse, or insulin, chemotherapy, antacids, diuretics (minor) | — | — |
| Subcutaneous fat loss | — | Moderate | Severe |
| Muscle loss | — | Mild or moderate | Severe |
| Higher-risk comorbidity | — | Moderate disease | Severe disease |
The phosphate before feeding is not the one that kills
Refeeding syndrome is the fall in phosphate, potassium and magnesium, with fluid retention and thiamin deficiency, that follows feeding someone who has been starved. During starvation the body runs on fat and protein and its insulin is low. Food, especially carbohydrate, brings insulin back, and insulin drives phosphate, potassium and magnesium into cells to rebuild tissue and make ATP. The serum levels fall — sometimes within hours — and a phosphate that was normal on admission can be dangerously low on day two. Severe hypophosphataemia means weak respiratory muscles, heart failure, rhabdomyolysis, haemolysis and confusion.
So the useful question is not only how low the phosphate is, but who is at risk before the fall happens. NICE CG32 answers it with two lists, and reproducing them exactly matters because they are easy to half-remember. One or more of four major criteria — a BMI below 16, more than 15% unintentional weight loss in three to six months, little or no intake for more than ten days, or a low potassium, phosphate or magnesium before feeding — makes a patient high risk. So do two or more of four minor ones: a BMI below 18.5, more than 10% weight loss, more than five days of little intake, or a history of alcohol misuse or drugs including insulin, chemotherapy, antacids or diuretics. The page prints the count from each list so the reader can see which criteria tipped the answer.
ASPEN’s 2020 consensus uses a different structure — moderate risk with two criteria, significant risk with one — and different cut-offs, including shorter periods of weight loss and findings on examination. The table sets the two side by side. ASPEN also defines refeeding syndrome itself as a fall of 10% or more in phosphate, potassium or magnesium within five days of feeding, graded by size.
Not every low phosphate is refeeding. When it is low with no obvious cause, the renal tubular threshold for phosphate decides whether the kidney is leaking it (see the TmP/GFR calculator and the fractional excretion of phosphate calculator), and the phosphate unit converter converts units. Magnesium falls with it; see the hypomagnesaemia interpreter. This page supports clinical judgement and does not replace it.
Frequently asked questions
What are the NICE criteria for high risk of refeeding syndrome?
One or more of: BMI below 16, unintentional weight loss above 15% in 3 to 6 months, little or no intake for more than 10 days, or low potassium, phosphate or magnesium before feeding. Or two or more of: BMI below 18.5, weight loss above 10% in 3 to 6 months, little or no intake for more than 5 days, or a history of alcohol abuse or drugs including insulin, chemotherapy, antacids or diuretics.
How do the ASPEN 2020 criteria differ from NICE?
ASPEN has two tiers: moderate risk needs two criteria and significant risk one. It uses shorter weight-loss periods (5% in a month), counts loss of fat and muscle on examination and comorbidities, and does not list alcohol or drugs.
What phosphate level is severe?
Below 1 mg/dL (0.32 mmol/L). The Merck Manual calls 1 to 2 mg/dL (0.32 to 0.65 mmol/L) moderate and 2 to 2.5 mg/dL (0.65 to 0.81 mmol/L) mild.
How fast should feeding start in a high-risk patient?
NICE CG32: no more than 10 kcal/kg/day, or 5 kcal/kg/day in extreme cases, increased slowly over 4 to 7 days, with thiamin and electrolyte supplements. ASPEN: 100 to 150 g of dextrose or 10 to 20 kcal/kg for the first 24 hours.
How does ASPEN define refeeding syndrome?
A fall in phosphate, potassium or magnesium within 5 days of starting or increasing feeding: 10 to 20% mild, 20 to 30% moderate, more than 30% (or organ dysfunction or thiamin deficiency) severe.
Related calculators
References
- National Institute for Health and Care Excellence. Nutrition support for adults: oral nutrition support, enteral tube feeding and parenteral nutrition. Clinical guideline CG32. 2006, updated 2017. Recommendations 1.4.5–1.4.8.
- da Silva JSV, Seres DS, Sabino K, et al. ASPEN consensus recommendations for refeeding syndrome. Nutr Clin Pract. 2020;35(2):178–195. Erratum in Nutr Clin Pract. 2020;35(3):584–585.
- Lewis JL III. Hypophosphatemia. Merck Manual Professional Edition. Updated December 2025.
- Payne RB. Renal tubular reabsorption of phosphate (TmP/GFR): indications and interpretation. Ann Clin Biochem. 1998;35(2):201–206.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/