What does it measure?
This calculation divides CRP by albumin. During some illnesses, CRP rises while albumin falls, so the ratio brings those two changes together. Researchers have studied it for prognosis in settings such as sepsis; that setting matters when interpreting what the evidence can tell us. [1]
Before reading the calculation
- Inputs
- CRP and albumin measured at a comparable time in the illness.
- Calculation
- CRP ÷ albumin. Record both units: changing mg/L to mg/dL changes the number unless the formula is adjusted.
What can the result mean?
A higher ratio can reflect higher CRP, lower albumin, or both. Albumin can also fall with liver disease, protein loss, or fluid shifts. The ratio cannot distinguish these causes and should not be treated as a diagnosis of inflammation or malnutrition in an otherwise well person. [1] [2]
CRP and albumin measured at a comparable time in the illness.
- Calculation
- CRP ÷ albumin. Record both units: changing mg/L to mg/dL changes the number unless the formula is adjusted.
When is it useful, and how is it read?
CAR has been studied in defined illnesses, including sepsis prognosis. Outside those settings, first explain the separate CRP and albumin results. Kidney or liver findings may change the meaning of a low albumin without making CAR a diagnosis or wellness target. [1] [2]
What can affect it?
The numerical result depends on the units used for both tests. Ratios reported with different unit conventions cannot be compared directly. Results also change with the timing and severity of an illness, which limits casual comparisons over time. [1] [2]
A lower albumin can raise this ratio too
CAR increases if CRP rises, albumin falls, or both. Albumin can change for reasons beyond inflammation, so a higher ratio is not a direct measure of how much inflammation is in your body. [1] [2]
Questions you might have
Can I compare ratios from two laboratories directly?
Only after checking the component units and sampling context. The same blood concentrations can produce different-looking ratios under different unit conventions. [1]
Does a high ratio diagnose sepsis?
No. Studies in people with sepsis assessed prognosis; that does not turn the ratio into a stand-alone sepsis test. [1]
What comes next?
Review CRP and albumin separately before assigning meaning to the ratio. Your clinician can assess whether either result needs follow-up. Research in hospitalized patients does not establish a universal wellness threshold or prove that lowering the ratio itself improves health.
Do my CRP or albumin results need attention on their own, and what units were used?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
- Ranzani et al. — C-reactive protein/albumin ratio predicts 90-day mortality of septic patients (original study, 2013)
- MedlinePlus — Albumin blood test
Books we consulted
References that informed our explanations of the test and its context.
- Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Elsevier; 2019.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
