Aldolase Unit Converter
Aldolase Unit Converter
Convert serum aldolase between U/L, IU/L, µkat/L and nkat/L. Aldolase is a muscle enzyme read alongside creatine kinase in suspected inflammatory myopathy, and its reference interval belongs to a named method — two large laboratories publish adult limits that do not overlap.
Aldolase converter
Activity unitsAldolase 7.4 U/L
Formula and conversion factor
U/L = µkat/L × 60
nkat/L = U/L × 16.667
- U
- 1 unit = 1 µmol of substrate converted per minute under the assay’s own conditions
- kat
- 1 katal = 1 mol of substrate converted per second — the SI unit of catalytic activity
- ÷ 60
- the whole of the conversion. Per-minute against per-second, nothing else; no molecular weight is involved because activity is not a mass
- IU/L
- numerically identical to U/L. The I adds nothing here
- what does not convert
- a result reported in ng/mL or µg/L is a mass concentration measured by immunoassay, and there is no factor between it and U/L. The two tests count different things
Worked example
Aldolase 7.4 U/L
7.4 ÷ 60 = 0.123 µkat/L
= 123 nkat/L = 7.4 IU/L
Within Labcorp's 3.3–10.3 U/L interval for a kinetic assay at 37 °C
The same 7.4 U/L sits just under the top of ARUP's adult interval of 1.2–7.6 U/L — and a result of 8.0 U/L would be comfortably normal on the first interval and raised on the second. One sample, two answers
Two published adult intervals, and why they differ
| Source | Interval | Method as published |
|---|---|---|
| Labcorp, test 002030, over 1 year | 3.3 – 10.3 U/L | Kinetic, 340 nm, 37 °C |
| ARUP, test 0020012, 18 years and over | 1.2 – 7.6 U/L | Quantitative enzymatic assay, temperature not stated |
| Labcorp, 31 days to 1 year | 5.0 – 11.7 U/L | Kinetic, 340 nm, 37 °C |
| ARUP, 7 to 17 years | 3.3 – 9.7 U/L | Quantitative enzymatic assay |
Reading aldolase next to creatine kinase
| Aldolase | Creatine kinase | What it suggests |
|---|---|---|
| Raised | Raised | Muscle. The usual pattern in inflammatory myopathy, rhabdomyolysis, dystrophy or recent exertion — creatine kinase carries the information and aldolase adds little |
| Raised | Normal | Worth pursuing. In a small case series this combination predicted a myopathy with perimysial pathology, of the kind seen with antisynthetase antibodies |
| Normal | Raised | The common situation. Aldolase is less sensitive than creatine kinase for most muscle disease and a normal result does not exclude it |
| Raised | Normal, with abnormal liver tests | Consider liver rather than muscle — aldolase is also present in hepatocytes — and consider haemolysis, since red cells contain it too |
A second muscle enzyme, and the narrow case for measuring it
Aldolase A is a glycolytic enzyme that splits fructose-1,6-bisphosphate, and it is abundant in skeletal muscle. Damaged muscle releases it into serum in the same way it releases creatine kinase, which is why the two rise together in rhabdomyolysis, in the muscular dystrophies, in polymyositis and dermatomyositis, and for several days after unaccustomed exercise, an intramuscular injection or needle electromyography. For most of those situations creatine kinase is the better test: it is more sensitive, more specific to muscle, and available everywhere. Ordering both routinely adds cost and very little information.
The case for aldolase is narrower and rests on the discordant result. Nozaki and Pestronk described twelve patients with a raised serum aldolase and a normal creatine kinase: almost all had muscle discomfort, half had proximal and distal weakness, and 92% had perimysial pathology on biopsy — fragmented connective tissue with acid-phosphatase-positive cellularity, the pattern associated with antisynthetase antibodies. Twelve patients is a small series and the page states the number rather than the conclusion. The practical reading is that in a patient with muscle pain, suspected inflammatory myopathy and a normal creatine kinase, an aldolase is worth adding before concluding the muscle is normal.
Aldolase is not specific to muscle. Isoenzyme A dominates in muscle and red cells, B in liver and kidney, C in brain, and the routine assay measures total activity. So a raised aldolase can come from hepatocellular injury, from haemolysis in vitro or in vivo, and occasionally from tumour. Check the transaminases and look at the sample quality before attributing it to muscle. In the other direction, hereditary fructose intolerance is a deficiency of aldolase B, which is a genetic diagnosis and not something a serum activity is used to make.
An enzyme activity is defined by the assay that measured it — its substrate, its buffer, its temperature. A reference interval belongs to that method and does not travel to another one, which is why the interval on your own report is the one to read the result against. Aldolase makes the point more sharply than most. Labcorp publishes 3.3 to 10.3 U/L above one year of age for a kinetic assay read at 340 nm and 37 °C; ARUP publishes 1.2 to 7.6 U/L for adults. A result of 2.0 U/L is normal in the first laboratory and subnormal in the second, and a result of 9 U/L is normal in the first and raised in the second. The conversion this page performs — divide by sixty for µkat/L — is exact and universal. The interval it is read against is not.
Frequently asked questions
How do I convert aldolase from U/L to µkat/L?
Divide by 60. An aldolase of 7.4 U/L is 0.123 µkat/L, or 123 nkat/L. IU/L and U/L are the same number. The factor comes from the definitions — one unit is one µmol per minute, one katal is one mol per second — so it holds for every enzyme activity.
What is a normal aldolase?
It depends on the method, and by more than most people expect. Labcorp gives 3.3 to 10.3 U/L above one year of age for a kinetic assay at 37 °C; ARUP gives 1.2 to 7.6 U/L for adults. Use the interval printed on your own report.
Why measure aldolase if creatine kinase is available?
In most muscle disease you should not: creatine kinase is more sensitive and more muscle-specific. The exception is a patient with muscle symptoms and a normal creatine kinase, where a raised aldolase has been associated with a myopathy showing perimysial pathology — a small series of twelve patients, but the one situation where the test changes anything.
Does a normal aldolase exclude myositis?
No. Aldolase is less sensitive than creatine kinase in most inflammatory myopathy, and both can be normal in active disease, particularly in dermatomyositis and in inclusion body myositis. Normal muscle enzymes do not rule out a myopathy that the history and examination suggest.
What else raises aldolase besides muscle?
Liver injury, since aldolase B is a hepatic isoenzyme and the routine assay measures total activity; haemolysis, in the patient or in the tube, because red cells are rich in aldolase A; and occasionally malignancy. Check the transaminases and the sample before calling it muscle.
Related calculators
References
- Nozaki K, Pestronk A. High aldolase with normal creatine kinase in serum predicts a myopathy with perimysial pathology. J Neurol Neurosurg Psychiatry. 2009;80(8):904–908.
- Labcorp. Aldolase, test 002030. Reference interval 3.3–10.3 U/L above 1 year; kinetic assay, 340 nm, 37 °C.
- ARUP Laboratories. Aldolase, Serum, test 0020012. Reference interval 1.2–7.6 U/L for 18 years and older.
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.