Igg Synthesis Rate Calculation

IgG Synthesis Rate Calculator

Results

0.00 mg/day

function calculateIgGSynthesis() { var sIgG = parseFloat(document.getElementById('serumIgG').value); var cIgG = parseFloat(document.getElementById('csfIgG').value); var sAlb = parseFloat(document.getElementById('serumAlb').value); var cAlb = parseFloat(document.getElementById('csfAlb').value); if (isNaN(sIgG) || isNaN(cIgG) || isNaN(sAlb) || isNaN(cAlb) || sAlb === 0) { alert("Please enter valid numerical values. Serum Albumin cannot be zero."); return; } // Tourtellotte Formula: // Rate (mg/day) = [(IgG_CSF – IgG_Serum/369) – (Alb_CSF – Alb_Serum/230) * (IgG_Serum/Alb_Serum) * 0.43] * 5 var part1 = cIgG – (sIgG / 369); var part2 = (cAlb – (sAlb / 230)) * (sIgG / sAlb) * 0.43; var rate = (part1 – part2) * 5; var resultBox = document.getElementById('igg-result-box'); var display = document.getElementById('iggResultDisplay'); var interpretation = document.getElementById('iggInterpretation'); resultBox.style.display = 'block'; display.innerHTML = rate.toFixed(2) + " mg/day"; if (rate > 3.3) { interpretation.innerHTML = "Interpretation: Elevated synthesis rate. This suggests increased intrathecal IgG production, often associated with inflammatory conditions like Multiple Sclerosis."; interpretation.style.color = "#c0392b"; } else if (rate < 0) { interpretation.innerHTML = "Interpretation: Normal synthesis rate (Negative values are physiologically considered 0). No evidence of increased intrathecal production."; interpretation.style.color = "#27ae60"; } else { interpretation.innerHTML = "Interpretation: Normal synthesis rate (Reference range: < 3.3 mg/day)."; interpretation.style.color = "#27ae60"; } }

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Understanding the IgG Synthesis Rate

The IgG synthesis rate is a critical diagnostic metric used by neurologists to evaluate the central nervous system (CNS) for signs of local antibody production. This measurement helps distinguish between IgG that has leaked from the blood into the cerebrospinal fluid (CSF) and IgG that is being actively produced within the brain and spinal cord.

The Tourtellotte Formula

The calculator uses the established Tourtellotte formula, which accounts for the permeability of the blood-brain barrier by using albumin as a reference marker. Since albumin is exclusively produced in the liver, its presence in the CSF is entirely due to leakage from the blood. By comparing the ratios of IgG and albumin in both serum and CSF, we can calculate the surplus IgG produced daily.

Why is this Test Performed?

Measuring the intrathecal IgG synthesis rate is standard practice when investigating several neurological conditions, most notably:

• Multiple Sclerosis (MS): Roughly 90% of MS patients show evidence of abnormal IgG production.
• Neurosyphilis: CNS infections often trigger localized immune responses.
• Encephalitis: Viral or autoimmune inflammation of the brain tissue.
• Meningitis: Chronic inflammatory processes in the meninges.

Clinical Examples

Consider a patient with the following laboratory results:

• Serum IgG: 1100 mg/dL
• CSF IgG: 8.5 mg/dL
• Serum Albumin: 4200 mg/dL
• CSF Albumin: 28 mg/dL

Using the formula, this patient would result in an IgG synthesis rate of approximately 14.25 mg/day. This value is significantly higher than the normal threshold of 3.3 mg/day, indicating active neuroinflammation or an immune-mediated process within the CNS.

Important Limitations

While a high synthesis rate is indicative of CNS inflammation, it is not specific to one disease. Results must always be interpreted in the context of clinical symptoms, MRI findings, and other CSF studies such as Oligoclonal Bands (OCBs). A negative or normal IgG synthesis rate does not entirely rule out Multiple Sclerosis, though it does decrease the statistical likelihood.

Disclaimer: This calculator is intended for educational purposes for healthcare professionals and students. It is not a substitute for professional medical advice, diagnosis, or treatment.