Red Cell Distribution Width-Standard Deviation (RDW-SD) is a blood test parameter that measures the variability in the size of your red blood cells. It's one of the ways scientists assess the volume and size of red blood cells within a sample. A standard complete blood count (CBC) will often include RDW as it measures many different parts of your blood, including red blood cells. RDW can be reported in different ways, depending on the types of hematology analyzer instruments used, commonly as RDW-CV (Coefficient of Variation) or RDW-SD (Standard Deviation).

The RDW-SD specifically refers to the standard deviation of red blood cell volume, indicating how much the size of red blood cells varies around the average size. Normal RDW-SD levels are typically between 39-46 fL for adults. When the RDW-SD level is higher than normal, it may suggest that there is a significant variation in the size of red blood cells, which can be a symptom of various health conditions, such as anemia, liver disease, or other medical issues.

Red blood cells carry oxygen from the lungs to the rest of the body. They also carry carbon dioxide back to the lungs so it can be exhaled. Red blood cells (RBC) are made in the bone marrow and contain hemoglobin, a protein that carries oxygen to the tissues in the body. These cells are also known as erythrocytes.

Anemia is a condition that results from a decrease in the number of RBCs. Elevated RBC counts are seen in other conditions where there is low oxygen levels, certain drugs, kidney disease, or bone marrow overproduction. If your RBC count results are abnormal, additional tests are usually done to diagnose the cause of the high or low level of red blood cells.

A CBC measures two other components of your red blood cells:

- hemoglobin: oxygen-carrying protein

- hematocrit: percentage of red blood cells in your blood

Abnormal levels of red blood cells, hemoglobin, or hematocrit may be a sign of anemia, heart disease, or too little iron in your body.

Red blood cells can enter the urine from the vagina in menstruation or from the trauma of bladder catheterization (a procedure used to diagnose and treat cardiovascular conditions).

Renin is an enzyme produced by the kidney that can raise blood pressure levels. The renin activity plasma test helps your doctor determine whether or not your high blood pressure is due to poor kidney health.

The reptilase clotting time measures the rate of fibrin clot formation after the addition of reptilase, a proteolytic enzyme derived from the venom of Bothrops atrox, to citrated plasma.

Reptilase is a thrombin-like enzyme. 

Unlike thrombin, which cleaves fibrinogen to produce fibrinopeptides A and B, reptilase cleaves the fibrinogen molecule to release only fibrinopeptide A.

This section explores the presence and abundance of a panel of antibiotic resistance genes in the gut microbiome, and compares that to healthy population. The resistome is the sum of antimicrobial resistance genes in your gut. High number of resistance functions in your gut will make pathogens less likely to be sensitive to antibiotics and may be an indication that virulent strains are flourishing.

Reticulocyte Hemoglobin Equivalent (Retic Hgb Equivalent) is an invaluable marker in hematology, gaining prominence for its role in assessing iron status and erythropoiesis in clinical settings. This marker measures the hemoglobin content in reticulocytes, which are immature red blood cells recently released from the bone marrow. Retic Hgb Equivalent provides critical insights into the iron available for new red blood cell production, making it a vital tool for diagnosing and managing iron deficiency anemia and other disorders of red blood cell production.

Reticulocytes are newly produced, relatively immature red blood cells (RBCs). A reticulocyte test determines the number and/or percentage of reticulocytes in the blood and is a reflection of recent bone marrow function or activity.

Reticulocyte hemoglobin (Ret-He) is a crucial indicator in hematology, measuring hemoglobin in immature red blood cells, or reticulocytes. It's pivotal for diagnosing and managing anemia, especially iron deficiency anemia. Ret-He offers an early sign of iron deficiency, aiding in prompt intervention. This measure is more dynamic than traditional markers like serum ferritin, reflecting real-time iron availability for red blood cell production. Its inclusion in modern blood count analyzers underscores its importance in accurate diagnosis and patient care in iron-related disorders.

Reticulocytes are red blood cells that are still developing. They are also known as immature red blood cells. Reticulocytes are made in the bone marrow and sent into the bloodstream. About two days after they form, they develop into mature red blood cells. These red blood cells move oxygen from your lungs to every cell in your body.

RBP is a sensitive marker of undernutrition and the monitoring of its serum concentration allows the monitoring of nutritional status.

Retinol-binding protein (RBP) is an unglycosylated protein synthesised by the liver. The role of RBP is to transport retinol (vitamin A) from the liver to the target tissues (retina, skin, etc.) in the bloodstream. This protein is then metabolized, filtered and reabsorbed in the kidney.

Reverse T3 is a biologically inactive thyroid hormone; however, it does block the conversion of thyroxine (T4) to triiodothyronine (T3). Higher levels of reverse T3 can decrease the effect of thyroid hormone.