CK-MB Mass Unit Converter
CK-MB Mass Unit Converter
Convert CK-MB mass between ng/mL, µg/L and mg/L — the first two are the same number. The reason this page is separate from the activity one is that CK-MB mass and CK-MB activity are different measurands with different units and different reference intervals, and there is no factor between them.
CK-MB mass converter
Mass units onlyCK-MB mass 12 ng/mL
The ladder, and the conversion that does not exist
1 mg/L = 1,000 ng/mL, so ng/mL ÷ 1,000 = mg/L
ng/mL → U/L: no conversion exists
- ng/mL = µg/L
- a nanogram in a millilitre is a microgram in a litre. The thousandfold in the prefix cancels the thousandfold in the volume, so the number does not move. Manufacturers’ inserts print the two together for exactly this reason
- mg/L
- a thousand micrograms make a milligram, so mg/L is the ng/mL figure divided by a thousand. Rare on a cardiac report, and it makes a normal result look like a rounding error, which is why ng/mL is the reporting unit everywhere
- no molar unit
- CK-MB mass is standardised against a recombinant protein calibrator — the AACC reference material for creatine kinase mass assays — and not against a molar mass. There is nothing to divide a mass concentration by, so no nmol/L or pmol/L is offered
- U/L, IU/L, µkat/L
- these belong to the other CK-MB test, the catalytic activity assay, and there is no factor between an activity and a mass. A threshold in ng/mL applied to a U/L result, or the reverse, is meaningless
- the relative index
- the published cut-offs for CK-MB divided by total CK are defined for the mass assay, in ng/mL, against a total CK in U/L. That mixture of units is deliberate and correct — the index is a convention, not a dimensionless ratio
Worked example
CK-MB mass 12 ng/mL
12 ng/mL is 12.0 µg/L — the same number
12 ÷ 1,000 = 0.012 mg/L
Above both reference figures quoted above, and above the 9 ng/mL at which one hospital laboratory comments that the result is consistent with myocardial injury
It cannot be expressed in U/L at all. If you need the activity scale, that is the CK-MB activity converter
With a total CK of 600 U/L this is a relative index of 2.0%, which favours skeletal muscle — computed on the CK-MB relative index calculator
Named reference figures for CK-MB mass, and their methods
| Source | Method | Figure (ng/mL = µg/L) | What the source says with it |
|---|---|---|---|
| UW Medicine Laboratory Test Guide | Chemiluminescence immunoassay | 0–5 | "CK-MB Mass >9 ng/mL consistent with myocardial injury or infarction" |
| Abbott i-STAT CK-MB cartridge | Two-site enzyme-linked immunosorbent assay | 0.0–3.5 | That is the 0–95% range of results from healthy donors; "Each facility should establish its own reference range" |
| Abbott i-STAT CK-MB cartridge, reportable range | As above | 0.0–150.0 | Results above it are returned as ">150.0 ng/mL" rather than as a number |
| Abbott i-STAT CK-MB cartridge, calibration | As above | — | Values "are traceable to the American Association of Clinical Chemists (AACC recombinant human CK-MB from Seradyn Inc.) calibrator for the standardization of creatine kinase mass assays" |
Mass and activity: the two reference intervals, side by side
| CK-MB mass | CK-MB activity | |
|---|---|---|
| Unit | ng/mL, µg/L | U/L, IU/L, µkat/L |
| What a normal result looks like | 0–5 ng/mL on one hospital laboratory’s immunoassay | Reported as positive above the 99th percentile of normal, given as 5 to 25 IU/L |
| Anchored to | A recombinant CK-MB protein calibrator | The definition of the unit — one micromole of substrate per minute |
| Usable in the relative index | Yes; the cut-offs are defined for it | No |
| Converting to the other | Not possible | Not possible |
| Its own page | this page | CK-MB activity converter |
What CK-MB is still for: three claims against their sources
| The claim | What the source actually says |
|---|---|
| CK-MB is the test for diagnosing a myocardial infarction | It is not. StatPearls states that "Troponin has been established as the biomarker of choice for detecting myocardial damage of any etiology", and the Fifth Universal Definition of Myocardial Infarction (2026) builds its criteria entirely on cardiac troponin. |
| CK-MB is still needed for early re-infarction, because troponin is still up from the index event | This is the claim most often repeated, and current guidance has withdrawn it. StatPearls does say that "In cases where reinfarction is suspected, CK-MB may be useful for classifying a new event, given its shorter plasma elevation duration". But the published commentary on the 2018 Fourth Universal Definition states flatly that "Analysis of creatine kinase MB isoform (CK-MB) is not useful or cost-effective in the differential diagnosis of myocardial reinfarction when the cTn can be determined", and the Fifth Universal Definition instead uses serial troponin, noting that "Injury is more likely to be chronic and stable than progressive if the change is less than 20% between troponin measurements". |
| CK-MB is at least still used after cardiac surgery | Only as a fallback, and with a caveat attached. The Fifth Universal Definition describes criteria after coronary artery bypass grafting that use troponin thresholds "up to 170 times the URL or using less sensitive and specific biomarkers, such as creatine kinase-muscle/brain isoenzyme (CK-MB), which may no longer be widely available". |
Why the mass assay needs its own page
Two units on this page are the same number and the third is a thousandth of it. A nanogram per millilitre and a microgram per litre are identical — the thousandfold in the prefix cancels the thousandfold in the volume — which is why manufacturers print them together, as "ng/mL (µg/L)", rather than offering a factor. Milligrams per litre divides by a thousand and turns a normal result into 0.003, which is why nobody reports CK-MB that way. There is no molar unit, because a CK-MB mass assay is calibrated against a recombinant protein reference material rather than against a molar mass, and there is no conversion to units per litre, because that is a different test.
That last sentence is the whole reason this page exists separately from the CK-MB activity converter. Creatine kinase MB can be measured two ways that share a name and share nothing else. A mass assay uses two antibodies to count how much CK-MB protein is present and reports nanograms per millilitre. An activity assay measures how fast the enzyme converts its substrate and reports units per litre, a unit being one micromole of substrate turned over per minute. One is a concentration, the other is a rate. No factor relates them, the reference intervals are unrelated numbers — around 0 to 5 ng/mL against a 99th percentile given as 5 to 25 IU/L — and the published cut-offs for the relative index are defined for the mass assay only. The practical failure mode is mundane and common: a result in U/L is read against a threshold in ng/mL, the number looks several-fold high, and somebody worries about an infarct that the numbers never said anything about.
Even within the mass assay, the interval is not a constant. A hospital laboratory quotes 0 to 5 ng/mL by chemiluminescence and comments that above 9 ng/mL the result is consistent with myocardial injury; the instructions for a point-of-care cartridge give 0.0 to 3.5 ng/mL as the range spanning ninety-five per cent of healthy donors and tell the reader in the same paragraph that each facility should establish its own. Both are correct for their own method. CK-MB mass assays were never harmonised the way troponin has been standardised against the ninety-ninth percentile of a defined reference population, so the interval printed beside the result is the one that applies to it, and a figure copied from anywhere else — including this page — is not.
It is worth being straight about what the test is now for, because the honest answer has changed. High-sensitivity troponin is more cardiac-specific, rises earlier and is what the current universal definition of myocardial infarction is built on; CK-MB is described there as one of the less sensitive and specific biomarkers that may no longer be widely available. The residual indication everybody quotes — that CK-MB clears faster than troponin and therefore detects a second infarct while the troponin is still elevated from the first — is real physiology and has nonetheless been withdrawn as advice. The commentary on the Fourth Universal Definition says in as many words that CK-MB is not useful or cost-effective for the differential diagnosis of re-infarction when troponin can be measured, and the Fifth handles the same question with serial troponins, treating a change of less than twenty per cent between measurements as chronic rather than progressive injury. If you are holding a CK-MB mass result, convert it, read it beside a troponin from the same draw, and if the question is heart against skeletal muscle, put it into the CK-MB relative index calculator with a total CK from the same sample. Those are the two things it can still do.
Frequently asked questions
How do I convert CK-MB from ng/mL to µg/L?
You do not need to: they are the same number. One nanogram in a millilitre is one microgram in a litre, because the prefix and the volume both change by a factor of a thousand and cancel. Manufacturers’ inserts print CK-MB results as "ng/mL (µg/L)" for that reason. Milligrams per litre, if you ever meet it, is the ng/mL figure divided by a thousand.
Is CK-MB mass the same as CK-MB activity?
No, and nothing converts between them. A mass assay counts CK-MB protein with a two-site immunoassay and reports ng/mL; an activity assay measures how fast the enzyme turns over its substrate and reports U/L. They are a concentration and a rate, with unrelated reference intervals — roughly 0 to 5 ng/mL against a 99th percentile given as 5 to 25 IU/L. Applying a mass threshold to an activity result is the commonest error with this test.
What is a normal CK-MB mass?
It depends on the method and is not harmonised. One hospital laboratory gives 0 to 5 ng/mL by chemiluminescence and flags results above 9 ng/mL as consistent with myocardial injury; a point-of-care ELISA cartridge gives 0.0 to 3.5 ng/mL as the healthy-donor range and instructs each facility to set its own. That is a 30% spread on the upper limit, so use the interval printed on your own report.
Why is there no nmol/L or pmol/L for CK-MB mass?
Because the assay is anchored to a protein calibrator rather than to a molar mass. The i-STAT insert states that its CK-MB values are traceable to the AACC recombinant human CK-MB calibrator for the standardisation of creatine kinase mass assays — an agreed material, not a grams-per-mole figure. Offering a molar unit would mean inventing a molecular weight for a dimeric enzyme and presenting the assumption as a conversion.
Is CK-MB still used to diagnose a heart attack or to detect re-infarction?
Not in current guidance. Troponin is the biomarker of choice for myocardial injury of any cause, and the Fifth Universal Definition of Myocardial Infarction (2026) is built on cardiac troponin, describing CK-MB as less sensitive and specific and possibly no longer widely available. The re-infarction argument — that CK-MB clears faster — was explicitly set aside by the commentary on the Fourth Universal Definition, which states that CK-MB is not useful or cost-effective for that purpose when troponin can be measured. Serial troponin with a change of more than 20% is used instead.
Can I put a CK-MB mass result into the relative index?
Yes — that is what the index is defined for. The published cut-offs of roughly 3% and 5% use CK-MB mass in ng/mL divided by total CK in U/L, multiplied by 100. Take both from the same draw, because the two markers clear at different rates and an index built from samples hours apart means nothing. An activity result in U/L cannot be used.
Related calculators
References
- Abbott Point of Care. CK-MB/ (CK-MB) cartridge instructions, i-STAT System. "ng/mL (µg/L)"; reportable range "0.0 to 150.0 ng/mL"; healthy-donor 0–95% range "0.0 ng/mL (µg/L) to 3.5 ng/mL (µg/L)"; two-site ELISA; traceable to the AACC recombinant human CK-MB calibrator.
- UW Medicine Laboratory Test Guide. CK MB Mass. Reference interval 0–5 ng/mL by chemiluminescence; "CK-MB Mass >9 ng/mL consistent with myocardial injury or infarction".
- StatPearls. Creatine Kinase MB: Diagnostic Utility and Limitations. NCBI Bookshelf NBK557591. Reported in mass units (ng/mL) or activity units (IU/L); positive above the 99th percentile, given as 5 to 25 IU/L; rises 4–6 hours after symptom onset, peaks at 24 hours, normal by 48–72 hours; troponin is the biomarker of choice.
- Joint ESC/ACC/AHA/WHF Task Force. Fifth Universal Definition of Myocardial Infarction (2026). CK-MB described among "less sensitive and specific biomarkers … which may no longer be widely available"; a change of less than 20% between troponin measurements favours chronic over progressive injury.
- Comments on the 2018 ESC Fourth Universal Definition of Myocardial Infarction. Rev Esp Cardiol (Engl Ed). 2018. "Analysis of creatine kinase MB isoform (CK-MB) is not useful or cost-effective in the differential diagnosis of myocardial reinfarction when the cTn can be determined."
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.