Common Registration Assessment, Part 1
Renal dose adjustments using provided bands
Three original questions on creatinine clearance and band tables, with the working shown and the usual traps pointed out.
Published 4 October 2026. Independent revision material, not GPhC questions, not for patient care.
Renal questions in the assessment hand you the formula and the dose bands. Your job is arithmetic: estimate the creatinine clearance, find the right band, and apply the stated adjustment.
The questions here are fictional and practise only the arithmetic. Use the formula and the table exactly as printed, even if you know a different version from practice.
The method
- Write the provided creatinine clearance formula and each value with its unit.
- Choose the provided factor for sex and substitute carefully.
- Divide through to get the clearance in mL/min.
- Read across to the provided band table.
- Apply the band's instruction to the stated dose.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
Using the provided formula CrCl = (140 - age) x weight x F / serum creatinine, with F = 1.23 for men and creatinine in micromol/L: a 70-year-old man weighs 80 kg with a creatinine of 110 micromol/L. The provided table says full dose above 60 mL/min, half dose at 30 to 60. What is the CrCl and the dose?
Show the answer
Answer: 62.6 mL/min, full dose
Working: (140 - 70) x 80 x 1.23 / 110 = 6,888 / 110 = 62.6 mL/min, which is above 60, so the full dose applies.
Question 2
Using the same provided formula with F = 1.04 for women: a 65-year-old woman weighs 60 kg with a creatinine of 150 micromol/L. The same table applies. What is the CrCl and the dose?
Show the answer
Answer: 31.2 mL/min, half dose
Working: (140 - 65) x 60 x 1.04 / 150 = 4,680 / 150 = 31.2 mL/min, inside the 30 to 60 band, so half dose.
Question 3
Using the same provided formula: an 82-year-old man weighs 68 kg with a creatinine of 180 micromol/L. The table says quarter dose below 30 mL/min. What is the CrCl and the dose?
Show the answer
Answer: 27 mL/min, quarter dose
Working: (140 - 82) x 68 x 1.23 / 180 = 4,851 / 180 = 27.0 mL/min, below 30, so quarter dose.
Formula, then table
Two lookups, nothing more. Substitute into the provided formula, then read the provided table for the band your answer falls in.
Where marks are lost
- Using the wrong sex factor from the provided formula.
- Rounding the clearance before comparing it with the band boundaries.
- Applying a band from memory instead of the table printed in the question.
Frequently asked questions
Which creatinine units does the formula expect?
Whatever the provided formula states. These questions use micromol/L, which is the usual UK unit.
What if the clearance lands exactly on a boundary?
Read the table wording: bands are written as above, below or a range, and the printed wording decides.
Sources
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
- Energy content of parenteral nutrition
- Syringe driver rate calculations
- Area under the curve calculations
- 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.