The United States reports serum creatinine in mg/dL; most other countries use the SI unit µmol/L. The conversion factor is 88.4: multiply mg/dL by 88.4 for µmol/L, or divide µmol/L by 88.4 for mg/dL. The two numbers describe the same amount of creatinine in the blood — only the measurement scale differs.
The Conversion Formula
The relationship is a single fixed constant:
µmol/L = mg/dL × 88.4 and mg/dL = µmol/L ÷ 88.4
The constant 88.4 is not arbitrary. It derives from the molar mass of creatinine — about 113.12 g/mol — together with the step from decilitres to litres. Because it reflects a fixed chemical property of the molecule, the factor is the same everywhere and never needs updating. That makes the conversion exact rather than an approximation.
Worked Example
Suppose a lab in Europe reports a serum creatinine of 106 µmol/L and you need it in mg/dL for the Cockcroft–Gault equation. Divide by 88.4: 106 ÷ 88.4 = 1.2 mg/dL. Going the other way, a US value of 0.9 mg/dL becomes 0.9 × 88.4 = 79.6 µmol/L. The anchor worth memorising is that 1.0 mg/dL equals exactly 88.4 µmol/L.
Common Conversions and Normal Ranges
| mg/dL | µmol/L | Typical interpretation |
|---|---|---|
| 0.6 | 53 | Low end of normal |
| 0.9 | 80 | Mid-normal adult |
| 1.0 | 88 | Reference anchor (1.0 mg/dL = 88.4 µmol/L) |
| 1.3 | 115 | Upper limit of normal (many labs) |
| 2.0 | 177 | Clearly elevated |
| 4.0 | 354 | Markedly elevated |
Typical adult reference ranges are roughly 0.7–1.3 mg/dL (about 62–115 µmol/L) for men and 0.6–1.1 mg/dL (about 53–97 µmol/L) for women, though every laboratory sets its own range by assay and population. A high creatinine suggests reduced kidney filtration; see high creatinine for what raised values mean.
Why Units Matter for the Calculator
The Cockcroft–Gault creatinine clearance equation expects creatinine in mg/dL. Feeding it a µmol/L value without converting inflates the denominator roughly 88-fold and produces a near-zero clearance — a classic and dangerous unit error. Convert first, or simply select your unit in the calculator above, which accepts either and converts internally. The same caution applies to the eGFR equations, which are also written for mg/dL.
Where the Two Units Come From
The split is historical and geographic. The United States, alongside a few other countries, kept the older conventional mass-concentration unit, which reports how many milligrams of creatinine sit in a decilitre (one-tenth of a litre) of blood. Most of the world adopted the SI (Système International) convention, which reports concentration in moles per litre — here micromoles per litre, because creatinine is present in tiny amounts. Moles count molecules rather than mass, so the SI figure ties directly to the number of creatinine molecules present. Neither system is more correct; they are two languages describing one quantity, and the factor of 88.4 is the dictionary between them.
This matters in practice because medical literature, drug labels, and online calculators do not agree on a single unit. A guideline written in the United Kingdom may quote a creatinine threshold in µmol/L while a US drug label quotes the same threshold in mg/dL. Recognising which unit a source uses — and converting before you compare — prevents the most common and most dangerous arithmetic mistake in kidney calculations.
A Second Worked Example
A patient’s chart from an overseas hospital lists a creatinine of 176.8 µmol/L. To use it in a US-based calculator, divide by 88.4: 176.8 ÷ 88.4 = 2.0 mg/dL exactly. That value is clearly elevated and would prompt an estimate of kidney function. Going the other direction, a US chart showing 0.6 mg/dL converts to 0.6 × 88.4 = 53 µmol/L — the low end of normal. Because 88.4 is exact, these conversions introduce no error of their own; any uncertainty comes from the original measurement, not the arithmetic.
How to Read a Converted Value
Once converted, the number means exactly what it would have meant in its native unit. A creatinine of 1.0 mg/dL (88.4 µmol/L) sits comfortably mid-range for most adults. A value of 1.5 mg/dL (about 133 µmol/L) is mildly raised and usually prompts an estimate of kidney function. A value of 3.0 mg/dL (about 265 µmol/L) is clearly elevated and points to substantially reduced filtration. The conversion does not change that interpretation — it only lets you place the value against whichever reference range your lab reports. Remember that creatinine also depends on muscle mass: a muscular person and a frail person with the same true kidney function will not show the same creatinine, which is one reason a clearance estimate is more informative than the raw value.
Practical Conversion Tips
- To go from US to SI, multiply by 88.4 (roughly ×90 for a quick mental estimate).
- To go from SI to US, divide by 88.4 (roughly ÷90 for a quick mental estimate).
- Anchor on 1.0 mg/dL = 88.4 µmol/L; scale up or down from there.
- When in doubt, let the calculator do it — pick your unit and it converts internally before applying the equation.
Limitations and Notes
- µmol/L is the SI (Système International) unit; mg/dL is a conventional mass-concentration unit. The conversion changes only the unit, never the underlying physiology.
- Rounding to one or two decimal places is fine for clinical use; the table above is rounded for readability.
- This converter handles serum creatinine only. Urine creatinine, used in the albumin/creatinine and protein/creatinine ratios, is reported in different units and is not interchangeable here.
- Never convert creatinine to creatinine clearance by a fixed factor — clearance also depends on age, sex, and weight.