CSF Albumin Quotient (Q-Albumin) Calculator
CSF Albumin Quotient (Q-Albumin) Calculator
Calculate Q-albumin, the single best measure of blood-CSF barrier integrity, from CSF and serum albumin.
CSF Albumin Quotient (Q-Albumin)
CSF albumin ÷ serum albuminCSF albumin 240 mg/L, serum albumin 42 g/L
Formula
- CSF albumin
- mg/L
- serum albumin
- g/L — note the different unit from CSF albumin
- ×1000 by convention
- mixing mg/L with g/L makes the quotient dimensionless times 1000, which is the conventional way Q-albumin is expressed
Worked example
CSF albumin 240 mg/L, serum albumin 42 g/L
240 ÷ 42 = 5.7
Below the typical adult upper limit of about 6.5–8 — an intact barrier
Age-dependent upper reference limit
| Age | Approximate upper limit of Q-albumin |
|---|---|
| Under 15 years | ≈ 5 |
| 15 – 40 years | ≈ 6.5 |
| 40 – 60 years | ≈ 8 |
| Over 60 years | ≈ 9 – 10 |
Q-albumin as a barrier test
Q-albumin is the single best measure of blood-CSF barrier integrity, because albumin is synthesised only in the liver and reaches CSF exclusively by crossing that barrier — any albumin found there reflects permeability, not local production. Note the units carefully: CSF albumin is conventionally expressed in mg/L and serum albumin in g/L, so the quotient is dimensionless multiplied by 1000 by convention, not a simple ratio of like units.
The upper reference limit is age-dependent and rises steadily through life: roughly 5 under 15 years, 6.5 up to 40, 8 up to 60, and 9 to 10 beyond that. Applying a single adult cut-off across all ages misclassifies both a normal elderly result as abnormal and, less often, a genuinely abnormal young result as borderline.
Marked elevation occurs in bacterial meningitis, Guillain-Barré syndrome, spinal block and severe polyneuropathy — conditions that either damage the barrier directly or obstruct CSF flow so that protein accumulates. A raised Q-albumin also invalidates a raw CSF protein or IgG measurement taken at face value, since both rise simply because more serum protein has crossed the barrier — which is exactly why the IgG index divides by Q-albumin, to separate barrier leakage from true intrathecal synthesis.
Frequently asked questions
What is Q-albumin?
CSF albumin divided by serum albumin, the standard measure of blood-CSF barrier integrity. Because albumin is made only in the liver, any albumin in CSF reflects how much has crossed the barrier.
Why are the units different for CSF and serum albumin?
By convention CSF albumin is reported in mg/L and serum albumin in g/L. The quotient works out as dimensionless times 1000, which is the standard way Q-albumin is expressed — do not convert both to the same unit first.
Does Q-albumin change with age?
Yes, and substantially. The upper reference limit rises from about 5 under 15 years to 9–10 beyond 60, reflecting normal age-related barrier permeability.
What causes a markedly raised Q-albumin?
Bacterial meningitis, Guillain-Barré syndrome, spinal block and severe polyneuropathy are the classic causes, either damaging the barrier directly or obstructing CSF flow so protein accumulates.
Related calculators
References
- Reiber H. Flow rate of cerebrospinal fluid (CSF) as a concept common to normal blood-CSF barrier function and to dysfunction in neurological diseases. J Neurol Sci. 1994;122(2):189–203.
- Deisenhammer F et al. Guidelines on routine cerebrospinal fluid analysis. Eur J Neurol. 2006;13(9):913–22.
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.