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C-reactive protein to albumin ratio shows non-linear association with stroke-associated pneumonia riskHigh CAR Score Means Higher Stroke Pneumonia Risk

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Key Takeaway
Consider CAR's non-linear threshold effect for SAP risk as preliminary, requiring prospective validation.

This retrospective cohort study analyzed 1,595 consecutive patients admitted with acute ischemic stroke between September 2016 and September 2022. The study investigated the C-reactive protein to albumin ratio (CAR) as a predictor for stroke-associated pneumonia (SAP), which occurred in 376 patients (23.6% of the cohort). The primary analysis revealed a strong association between log2-transformed CAR and SAP risk, with patients in the highest CAR quartile having an odds ratio of 6.11 (95% CI: 3.63–10.27, p < 0.05).

A key finding was the identification of a non-linear threshold effect at CAR ≈ 0.14. Below this threshold, the association with SAP was modest (OR = 1.22, 95% CI: 1.02–1.45). Above this threshold, the risk increased substantially (OR = 2.03, 95% CI: 1.70–2.42). The threshold-based predictive model statistically outperformed a simple linear model (p < 0.05).

Safety and tolerability data for the biomarker measurement were not reported. The authors explicitly note that the study establishes association only, not causation. A key limitation is that non-linear relationships and threshold effects for CAR in SAP prediction remain unclear and require further investigation. Funding sources and potential conflicts of interest were not disclosed.

For clinical practice, this study provides preliminary evidence for a potential biomarker threshold that may help stratify pneumonia risk in stroke patients. However, given the retrospective, observational design and the acknowledged uncertainty around the threshold effect, CAR should not yet be used to guide clinical decisions. Prospective validation is needed to confirm these findings and establish clinical utility.

Imagine waking up after a stroke, only to feel a new cough and fever hours later. This is stroke-associated pneumonia (SAP), a serious complication that hits 1 in 4 stroke patients. It turns a tough recovery into a dangerous battle. Doctors need a way to spot this risk early.

Stroke patients are often weak. Their immune systems struggle. Inflammation rises when the brain is injured. But nutrition drops too. This mix makes them vulnerable to lung infections. Current tools miss this specific danger. They look at blood tests separately. They do not combine them. This leaves a gap in patient care.

The surprising shift

Doctors used to think inflammation alone caused the risk. They looked at C-reactive protein (CRP) levels. They ignored low albumin (a protein in blood). But here is the twist. Low albumin changes how we read inflammation. A simple average score misses the real danger. A new method finds the hidden threshold.

What scientists didn't expect

Think of your body like a security system. CRP is the alarm bell ringing loudly. Albumin is the power supply keeping the lights on. If the power is low, the alarm sounds different. It is not just about the noise. It is about the battery level too. This combination creates a unique risk signal.

Researchers looked at 1,595 stroke patients. They studied records from 2016 to 2022. They calculated a score called the C-reactive protein to albumin ratio (CAR). They checked who got pneumonia and who did not. They used advanced math to find the pattern.

The study found a clear line in the sand. When the CAR score was below 0.14, the risk was low. But when the score crossed 0.14, the danger jumped. Patients with high scores were six times more likely to get pneumonia. This is a huge difference. It helps doctors see who needs extra protection.

But there is a catch.

This new score is not a magic wand. It is a warning light. It tells you to watch closely. It does not mean the infection is already there. It means you must be ready to act fast.

Where this fits in

Experts say this tool fits perfectly into current care. It uses numbers doctors already have. No new tests are needed. It adds clarity to confusing blood results. It helps teams decide who needs antibiotics sooner. It saves time and resources for the hospital.

If you or a loved one had a stroke, talk to your doctor about your blood work. Ask if your CRP and albumin levels are being checked together. If your score is high, ask about prevention steps. These steps might include better nutrition or closer monitoring. Early action stops small problems from growing.

The study has limits

This study looked at past records. It did not follow patients for years. The results are strong, but they are not perfect. Every patient is different. Your doctor knows your full story best. Always follow their specific advice.

More research will follow this study. Scientists will test this score in different hospitals. They will see if it works everywhere. Eventually, this could become a standard part of stroke care. Until then, it is a powerful new tool for doctors. It brings us closer to safer recovery for everyone.

Study Details

Study typeCohort
EvidenceLevel 3
PublishedApr 2026
View Original Abstract ↓
BackgroundStroke-associated pneumonia (SAP) complicates 10–30% of acute ischemic stroke (AIS) cases and worsens outcomes. The C-reactive protein to albumin ratio (CAR) integrates inflammation and nutritional status and may serve as a prognostic biomarker. However, non-linear relationships and threshold effects for CAR in SAP prediction remain unclear.MethodsWe retrospectively analyzed 1,595 consecutive AIS patients admitted between September 2016 and September 2022. CAR was calculated from admission CRP and albumin. Associations between CAR and SAP were assessed using multivariable logistic regression, generalized additive models (GAM), and two-piecewise regression to identify thresholds. Predictive performance was evaluated by ROC analysis and DeLong’s test.ResultsA total of 1,595 patients were included (58.6% male; mean age 70.1 ± 12.2 years). The median admission NIHSS score was 3.0 (IQR 1.0–6.0). SAP occurred in 376 patients (23.6%). Log₂-CAR was strongly associated with SAP risk (P-trend < 0.0001), with the highest quartile showing a fully adjusted OR of 6.11 (95% CI: 3.63–10.27, p  0.05). A non-linear threshold was identified at CAR ≈ 0.14; below this, the association was modest (OR = 1.22, 95% CI: 1.02–1.45), while above it, risk increased substantially (OR = 2.03, 95% CI: 1.70–2.42). The threshold model outperformed the linear model (p 
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