Calculatrice de Clairance de la Créatinine

Évaluez la fonction rénale en utilisant la formule de Cockcroft-Gault pour les ajustements de dose de médicaments

Âge (ans)

Poids (kg)

Créatinine Sérique (mg/dL)

Genre

Questions Fréquentes

1. Quelle est la différence entre la clairance de la créatinine et le GFR?

La Clairance de la Créatinine (CrCl) et le Taux de Filtration Glomérulaire (GFR) évaluent tous deux la fonction rénale mais sont calculés différemment. CrCl utilise la formule de Cockcroft-Gault basée sur la créatinine sérique, l'âge, le poids et le sexe. GFR utilise couramment les formules MDRD ou CKD-EPI et considère des facteurs supplémentaires comme la race. Dans la pratique clinique, les valeurs sont similaires, mais CrCl est plus souvent utilisé pour les ajustements posologiques des médicaments, tandis que GFR est préféré pour le staging et le diagnostic de l'IRC.

2. Pour qui la formule de Cockcroft-Gault convient-elle?

Convient aux adultes âgés de 18 à 110 ans, patients avec un poids stable et ceux avec une fonction rénale relativement stable. NE convient PAS aux femmes enceintes (changements significatifs de la masse musculaire), patients sévèrement dénutris ou obèses, amputés (masse musculaire réduite), patients avec des changements aigus de fonction rénale, ou enfants (utiliser des formules pédiatriques). La formule nécessite un jugement clinique pour les populations spéciales.

3. Comment le CrCl doit-il être calculé pour les patients obèses?

Pour les patients obèses (IMC > 30), utiliser le poids corporel actuel peut surestimer le CrCl. Les cliniciens utilisent couramment des méthodes ajustées: (1) Poids Corporel Idéal (IBW) basé sur la taille, (2) Poids corporel ajusté: IBW + 0.4 × (poids actuel - IBW), (3) Poids corporel maigre pour une estimation plus précise. Le calcul du CrCl chez les patients obèses doit être déterminé par les médecins ou pharmaciens basé sur les circonstances individuelles.

4. Une créatinine sérique normale signifie-t-elle une fonction rénale normale?

Pas nécessairement. Les niveaux de créatinine sérique sont influencés par de multiples facteurs: masse musculaire (personnes âgées, femmes, patients avec atrophie musculaire peuvent avoir une créatinine plus basse), régime (les végétariens peuvent avoir une créatinine plus basse, une haute consommation de viande peut l'augmenter), et compensation rénale (dans une maladie rénale précoce, les néphrons restants peuvent compenser en augmentant la filtration). Par conséquent, même avec une créatinine sérique "normale", les personnes âgées, faible masse musculaire ou populations à haut risque devraient calculer CrCl ou eGFR pour une évaluation précise de la fonction rénale.

5. Quels médicaments courants nécessitent un ajustement posologique basé sur le CrCl?

De nombreux médicaments nécessitent un ajustement de dose rénale: Antibiotiques (vancomycine, aminosides, certaines céphalosporines), Anticoagulants (dabigatran, rivaroxaban, apixaban), Médicaments antidiabétiques (metformine - contre-indiquée si eGFR < 30), Médicaments de chimiothérapie (carboplatine, méthotrexate), Antiviraux (aciclovir, ganciclovir), Analgésiques (certains opioïdes). Les ajustements de dose spécifiques doivent être consultés avec des médecins ou pharmaciens.

6. Quelles sont les applications cliniques de la clairance de la créatinine?

CrCl a de multiples applications cliniques: (1) Ajustement posologique des médicaments - de nombreux médicaments nécessitent un ajustement de dose basé sur la fonction rénale, CrCl < 30 mL/min nécessite généralement un ajustement significatif. (2) Évaluation de la fonction rénale - diagnostic et surveillance de la maladie rénale aiguë et chronique, évaluation de la progression de la maladie. (3) Utilisation d'agents de contraste - les patients avec CrCl < 60 mL/min ont besoin d'une évaluation des risques et d'hydratation pour prévenir la néphropathie de contraste. (4) Évaluation du risque chirurgical - évaluation préopératoire de la fonction rénale pour prédire les complications postopératoires. (5) Indication de dialyse - CrCl < 15 mL/min peut nécessiter une préparation à la dialyse. (6) Surveillance de la toxicité médicamenteuse - certains médicaments s'accumulent en cas d'insuffisance rénale.

Creatinine clearance estimates how much blood the kidneys filter per minute, using serum creatinine together with age, body weight and sex. It is the classic bedside estimate of kidney function and remains embedded in drug labelling: a large share of prescribing information specifies dose adjustments in terms of Cockcroft-Gault creatinine clearance rather than any newer measure, which is why the equation is still in daily use decades after better ones appeared for other purposes.

La formule

CrCl (mL/min) = [(140 - age) x weight] / (72 x serum creatinine)
Multiply by 0.85 if female

age = age in years
weight = body weight in kilograms
serum creatinine = in mg/dL
The 0.85 factor reflects lower average muscle mass, and therefore lower creatinine production, in women

Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron, 1976. The equation was fitted to 249 hospitalised men; the female correction factor was estimated rather than measured in that cohort.

How the calculation works

Creatinine is a waste product of muscle metabolism, produced at a roughly constant rate and cleared almost entirely by the kidneys. If production is steady, the concentration left in the blood is inversely related to how well the kidneys are filtering. The Cockcroft-Gault equation turns that relationship into a number by scaling inverse creatinine with body weight, as a proxy for muscle mass and therefore production, and subtracting age, because muscle mass and filtration both decline with age.

This is why the equation behaves oddly at the extremes of body composition. Weight enters as a direct multiplier, so using actual body weight in someone with obesity inflates the estimate, sometimes substantially. Common practice is to use ideal body weight, or adjusted body weight when actual weight exceeds ideal by more than about 30 percent, though the original paper specifies none of this and drug labels vary in what they assume.

How to read your result

The bands below are the ones used for drug dosing decisions. They are not the same as the chronic kidney disease stages, which are defined on estimated glomerular filtration rate normalised to body surface area, a different quantity computed a different way. A result here should be read as an input to a dosing question, not as a CKD stage.

Direct oral anticoagulants, many antibiotics, metformin, gabapentin and most renally cleared chemotherapeutics have labelled thresholds stated in Cockcroft-Gault terms.
A result close to a labelled cut-off deserves care: small differences in which weight was used can move the estimate across the boundary.

Creatinine clearance (mL/min)	Typical prescribing implication
90 and above	Normal filtration, standard dosing for most drugs
60 to 89	Mildly reduced, most drugs unchanged
30 to 59	Moderately reduced, many renally cleared drugs need dose or interval adjustment
15 to 29	Severely reduced, substantial dose reduction or avoidance for many agents
Below 15	Kidney failure range, specialist input required

Cockcroft-Gault versus eGFR

For staging chronic kidney disease, current guidance uses estimated glomerular filtration rate from the CKD-EPI equation, which was refit in 2021 to remove the race coefficient it previously contained. eGFR is reported automatically by most laboratories alongside creatinine and is normalised to a standard body surface area of 1.73 square metres, which makes it comparable between people of different sizes but not directly usable for weight-based drug dosing.

The two numbers therefore answer different questions and will not agree. Using eGFR where a drug label specifies creatinine clearance, or the reverse, can shift a dose across a threshold. When a decision hinges on the value, and particularly at the extremes of body size or muscle mass, a measured clearance from a timed urine collection or a cystatin C based estimate is more dependable than either equation.

Limites

The equation assumes creatinine production is stable. It is not valid during acute kidney injury, when serum creatinine is still rising or falling and lags behind actual filtration by a day or more.
Muscle mass drives creatinine production, so the estimate is unreliable in people who are very muscular, frail, malnourished, paraplegic, amputated, or on a vegetarian diet, all of which shift production away from what the equation assumes.
Using actual body weight in obesity overestimates clearance. Ideal or adjusted body weight is usually substituted, but practice differs between institutions and between drug labels.
Some drugs, including trimethoprim, cimetidine and cobicistat, block tubular secretion of creatinine. They raise serum creatinine without changing filtration, making kidney function look worse than it is.
The original cohort was 249 hospitalised men. The female correction factor and the performance in older adults, children and pregnancy were not established in that study; the equation is not used in children at all.
This calculator does not replace clinical assessment. Dosing decisions belong with the prescriber and pharmacist who can see the full picture, including the specific drug label.

Questions fréquentes

What is a normal creatinine clearance?

Roughly 90 to 140 mL/min in healthy young adults, higher in men than women on average, and declining gradually with age. Values are interpreted against the person and the clinical question rather than against a fixed normal range.

Why does the formula use a different factor for women?

Women have lower average muscle mass and therefore produce less creatinine, so the same serum creatinine corresponds to better filtration. The 0.85 multiplier corrects for this. It was an estimate in the original 1976 paper rather than a value derived from female participants.

Should I use Cockcroft-Gault or eGFR?

Use eGFR for staging chronic kidney disease and Cockcroft-Gault where a drug label specifies it, which is most renally cleared medicines. They are computed differently and normalised differently, so substituting one for the other can push a dose across a labelled threshold.

Which body weight should be entered?

Practice is to use actual body weight when it is close to ideal, ideal body weight in obesity, and adjusted body weight when actual exceeds ideal by more than about 30 percent. Because weight is a direct multiplier, the choice can change the result substantially.

Can a single creatinine result tell me my kidney function?

Only approximately, and only if it is stable. A creatinine drawn while kidney function is changing rapidly lags behind reality, and creatinine alone cannot distinguish reduced filtration from reduced muscle mass. Trends across several measurements are far more informative than one value.