Protein appears in nearly all body tissues, along with your enzymes, blood, and cerebrospinal fluid (CSF). Healthy CSF has a low amount of protein.‌

- Protein level, opening pressure, and CSF-to-serum glucose ratio vary with age.

- CSF protein concentration is one of the most sensitive indicators of pathology within the CNS. 

- The spinal fluid normally contains very little protein since serum proteins are large molecules that do not cross the blood-brain barrier. Most of the protein that is normally present is albumin.

- CSF protein concentration may rise due to 2 factors: either an increased permeability of the blood brain barrier allowing more protein and higher molecular weight proteins to enter the CSF or proteins may be synthezised within the cerebrospinal canal by inflammatory or other invading cells.

Normally very few white blood cells are present in CSF. A significant increase in white blood cells in the CSF can be caused by infection or inflammation of the central nervous system.

The CSF/Serum Albumin Index is a key diagnostic tool used to assess the integrity of the blood-brain barrier (BBB). It compares albumin concentrations in the cerebrospinal fluid (CSF) and serum. Since albumin is produced exclusively in the liver and not within the central nervous system (CNS), its presence in the CSF indicates passive diffusion across the BBB. An elevated index suggests increased permeability or disruption of the barrier, making it a reliable marker for BBB dysfunction.

Cyclic AMP (Cyclic adenosine-3′-5′-monophosphate) serves as a 2nd messenger in signal transmission of many hormones, such as adrenaline, ACTH, LH, FSH, glucagon, and calcitonin.

Cyclic citrullinated peptide antibodies are autoantibodies produced by the immune system that are directed against cyclic citrullinated peptides (CCP). This test detects and measures anti-CCP antibodies in the blood. Citrulline is naturally produced in the body as part of the metabolism of the amino acid arginine. However, in joints with rheumatoid arthritis (RA), this conversion may occur at a higher rate.

Cyclospora cayetanensis is a coccidian (= intestinal) parasite that causes a diarrheal disease known as cyclosporiasis in humans and possibly in other primates.

It belongs to the phylum Apicomplexa and the genus Cyclospora. The species name, "cayetanensis," refers to the Cayetano Heredia University in Lima, Peru, where early epidemiological and taxonomic work on this parasite was conducted.

Symptoms of cyclosporiasis include watery diarrhea, loss of appetite, weight loss, abdominal cramps, nausea, and sometimes low-grade fever. The severity of the illness can vary based on factors such as age, the condition of the host, and the size of the infectious dose.

Infection with Cyclospora cayetanensis occurs when individuals consume food or water contaminated with the parasite. People living or traveling in countries where cyclosporiasis is endemic may be at an increased risk of infection. The oocysts are shed in the stool of infected individuals and need favorable laboratory conditions to sporulate and become infective. Cyclosporiasis can also be acquired from contaminated produce, leading to outbreaks in developed countries.

How is Cyclospora infection treated?

The recommended treatment is a combination of two antibiotics, trimethoprim-sulfamethoxazole, also known as Bactrim, Septra, or Cotrim. People who have diarrhea should also rest and drink plenty of fluids.

This parasite causes an intestinal infection called cyclosporiasis.

The CYFRA 21-1 is well known as tumor maker of lung cancer and is not influenced by environmental factors.

CYRFA 21-1 (cytokeratin 19 fragment) has been demonstrated as clinically useful in the prognostication and monitoring of non-small cell lung cancer (NSCLC). Elevated pre-treatment levels may be associated with unfavorable prognosis, and decreasing levels during therapy predict an objective response to treatment. However, the level of CYFRA 21-1 cannot be used as absolute evidence for the presence or absence of disease and results must be viewed in context with other clinical evidence.

Cytokeratins are epithelial markers whose expression is not lost during malignant transformation. CYFRA 21-1 is a cytokeratin-19 fragment that is soluble in serum and can be used as circulating tumor marker. Although expressed in all body tissues, its major occurrence is in the lung, particularly in lung cancer tissues.

Hepatitis C virus (HCV) is an enveloped, positive-sense single-stranded RNA virus of the Flaviviridae family.

Cysteine is a nonessential sulfur-containing amino acid. It is obtained from the diet and is also endogenously made from the intermediate amino acid cystathionine.

Dietary cysteine sources include poultry, eggs, beef, and whole grains.

This amino acid should not be confused with the oxidized derivative of cysteine called cystine. Cystine is formed by combining two cysteine molecules within a redox reaction.

The urinary FMV amino acid test reports cysteine and cystine separately.

The plasma amino acid test combines both cysteine and cystine as one biomarker called "Cyst(e)ine".

Cysteine is a nonessential sulfur-containing amino acid. It is obtained from the diet and is also endogenously made from the intermediate amino acid cystathionine.

Dietary cysteine sources include poultry, eggs, beef, and whole grains.

This amino acid should not be confused with the oxidized derivative of cysteine called cystine. Cystine is formed by combining two cysteine molecules within a redox reaction.

The urinary FMV amino acid test reports cysteine and cystine separately.

The plasma amino acid test combines both cysteine and cystine as one biomarker called "Cyst(e)ine".

Cysteine is a nonessential sulfur-containing amino acid. It is obtained from the diet and is also endogenously made from cystathionine. Dietary cysteine sources include poultry, eggs, beef, and whole grains. [L]

Because cystathionine is an intermediate of the transsulfuration pathway, elevation of this biomarker may indicate a backup of the transsulfuration pathway. Conversion of cystathionine to glutathione requires necessary cofactors, such as vitamin B6, zinc, glycine, and magnesium. Therefore, transient elevations of this metabolite may indicate increased need for these cofactors.

Cystathionine is an intermediate dipeptide within the process of transsulfuration. Transsulfuration is the main route for irreversible homocysteine disposal, glutathione production, and energy. The initial step involves the enzyme cystathionine β-synthase enzyme (CBS). This reaction requires nutrient cofactors such as vitamin B6 and iron. Cystathionine is then converted to cysteine, and eventually goes on to either make glutathione or feed the Kreb’s cycle. Currently, there is no known source or physiologic function for cystathionine other than serving as a transsulfuration intermediate. Some literature suggests that cystathionine may exert protection against endoplasmic reticulum stress-induced tissue damage and cell death, but studies are sparse.

Cystathionine is an intermediate dipeptide within the process of transsulfuration.

Transsulfuration is the main route for irreversible homocysteine disposal, glutathione production, and energy. The initial step involves the enzyme cystathionine β-synthase enzyme (CBS). This reaction requires nutrient cofactors such as vitamin B6 and iron. Cystathionine is then converted to cysteine, and eventually goes on to either make glutathione or feed the Kreb’s cycle.

Cystathionine is an intermediate dipeptide within the process of transsulfuration. Transsulfuration is the main route for irreversible homocysteine disposal, glutathione production, and energy. The initial step involves the enzyme cystathionine β-synthase enzyme (CBS). This reaction requires nutrient cofactors such as vitamin B6 and iron. Cystathionine is then converted to cysteine, and eventually goes on to either make glutathione or feed the Kreb’s cycle. Currently, there is no known source or physiologic function for cystathionine other than serving as a transsulfuration intermediate. Some literature suggests that cystathionine may exert protection against endoplasmic reticulum stress-induced tissue damage and cell death, but studies are sparse.

Cystathionine is an intermediate dipeptide within the process of transsulfuration. Transsulfuration is the main route for irreversible homocysteine disposal, glutathione production, and energy. The initial step involves the enzyme cystathionine β-synthase enzyme (CBS). This reaction requires nutrient cofactors such as vitamin B6 and iron. Cystathionine is then converted to cysteine, and eventually goes on to either make glutathione or feed the Kreb’s cycle. Currently, there is no known source or physiologic function for cystathionine other than serving as a transsulfuration intermediate. Some literature suggests that cystathionine may exert protection against endoplasmic reticulum stress-induced tissue damage and cell death, but studies are sparse.