Common Registration Assessment, Part 1
Energy content of parenteral nutrition
Three original questions on energy from glucose and lipid, with the working shown and the usual traps pointed out.
Published 4 October 2026. Independent revision material, not GPhC questions, not for patient care.
Parenteral nutrition questions give you the energy density of each macronutrient and ask for the total in a bag, or the amount of one component needed to hit a target.
The questions here are fictional and practise only the arithmetic. The stems provide the energy values to use, so treat them as given and do not import figures from memory.
The method
- Write the provided energy value for each component, in kcal per gram.
- Convert volumes to masses using the percentage strength.
- Multiply each mass by its energy value.
- Add the contributions for a total, or subtract to find what glucose must supply.
- Convert a required glucose mass back to a volume if the question asks for one.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A fictional bag contains 200 g of glucose and 50 g of lipid. Using 4 kcal per gram for glucose and 9 kcal per gram for lipid, what is the total energy?
Show the answer
Answer: 1,250 kcal
Working: 200 x 4 = 800 kcal. 50 x 9 = 450 kcal. 800 + 450 = 1,250 kcal.
Question 2
A regimen gives 1 litre of 10% glucose and 250 mL of 20% lipid. Using the same provided values, how much energy does the patient receive?
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Answer: 850 kcal
Working: 10% of 1,000 mL = 100 g glucose, 100 x 4 = 400 kcal. 20% of 250 mL = 50 g lipid, 50 x 9 = 450 kcal. Total = 850 kcal.
Question 3
A fictional patient needs 1,800 kcal per day and receives 60 g of lipid. Using the same provided values, what volume of 50% glucose supplies the rest?
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Answer: 630 mL
Working: Lipid gives 60 x 9 = 540 kcal. Glucose must give 1,800 - 540 = 1,260 kcal, so 1,260 / 4 = 315 g. 315 g at 50% w/v = 315 / 0.5 = 630 mL.
Mass before energy
Convert every volume to a mass of nutrient first. Energy only ever multiplies a mass, never a volume.
Where marks are lost
- Using the volume of an emulsion as if it were the mass of lipid.
- Mixing the energy values up between glucose and lipid.
- Forgetting to divide by the percentage when turning a required mass back into a volume.
Frequently asked questions
Are the energy values the same in every question?
No. Use the values printed in the stem. Different products and different exam questions use different figures, and the provided values always win.
Does amino acid energy count?
Only if the stem tells you to count it and gives you a value. In these practice questions it is left out on purpose.
Sources
- The Pharmaceutical Journal, preparing for the GPhC pharmaceutical calculations assessment
- GPhC, 2026 assessment specification and permitted items
The questions above are original and use fictional drugs. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.
Practise until the method is automatic
Try 15 free questions with worked answers. No sign-up required.
More calculation topics
- Dose by weight calculations for the GPhC assessment
- Volume to give: liquid medicine calculations
- Percentage strength calculations: w/v, w/w and ratios
- Dilution calculations with C1V1 = C2V2
- Infusion rate calculations in mL per hour
- Drip rate calculations: drops per minute
- Body surface area calculations
- Creatinine clearance (Cockcroft-Gault) calculations
- Moles and millimoles calculations
- Displacement volume calculations for reconstitution
- Quantity to supply calculations
- Using a provided formula in calculations
- Dose information from packaging and labels
- Diluting a stock to a lower strength
- Medicine cost and switch calculations
- Rounding rules in calculations
- Enteral feed rate calculations
- Electrolyte content over time
- Infusion dose per kg per hour
- Rounding doses to measurable volumes
- Relative risk and relative risk reduction
- Absolute risk reduction and number needed to treat
- Odds ratio and confidence intervals
- Relative versus absolute risk reduction
- Loading dose and volume of distribution
- Top-up doses from measured drug levels
- Salt correction factors
- Mass and molar drug concentrations
- Half-life and falling drug levels
- Steady-state concentration and infusion rate
- Bioavailability and equivalent oral doses
- Oral maintenance dose and dosing interval
- Elimination rate constant and half-life
- Accumulation towards steady state
- Ratio strengths and one in X
- Serial dilution factors
- Mixing solutions of different strengths
- Tablet quantities for reducing regimens
- Equivalent doses from provided conversion tables
- Thresholds and dose-banding algorithms
- Unit conversions for mass and volume
- Units and units per mL
- Reconstituting powders and final concentration
- Millimoles and milliequivalents
- Infusion time and volume remaining
- Days supply from pack sizes
- Percentage w/v and w/w conversions
- Ideal and adjusted body weight from formulae
- Diluting creams and ointments by weight
- Scaling a formula to a batch size
- Age-band doses from a provided table
- Tablet fractions and split doses
- Stones, pounds, inches and metric conversions
- Micrograms per minute from mg per hour
- Percentage change and mark-up
- Molar solutions and mass per volume
- Osmolarity from component concentrations
- Direct proportion and cross-multiplication
- Scientific notation and very small quantities
- Stock use and reorder quantities
- Parts per million and very dilute solutions
- Sodium chloride equivalents and isotonic solutions
- Density and specific gravity conversions
- Doses per day and hours between doses
- Finding the volume of diluent to add
- Capping a dose at a stated maximum
- Whole vials and ampoules to draw up
- Reading values from a provided graph
- Micrograms per kg per minute infusions
- Percentage composition of a compound preparation
- Suppository displacement values
- Isotonicity by freezing point depression
- Syringe driver rate calculations
- Area under the curve calculations
- Renal dose adjustments using provided bands
- Insulin units and infusion calculations
- Working backwards from a stated dose
- Doses and days from multi-dose devices
- Combined additives in one infusion
See also the formula sheet, the eight sample questions and the approved calculator page.