A blood test is a specific type of laboratory analysis whereby a sample of blood is extracted from a vein in the arm using a needle or fingerprick. When multiple tests for specific blood components are performed, this is referred to as a blood panel or blood work. Cellular evaluation, including a complete blood count (CBC), can be an important contributing factor for diagnosing orthopedic disorders owing to infection and degenerative processes.
Blood counts of various types have been used for clinical purposes since the 19th century. Karl Vierordt was the first to perform blood counts; his techniques were described in a series of papers published in 1852.1 In 1855, Cramer introduced several important principles for blood counting, including the concept of a capillary space. During subsequent years, many different scientists and physicians developed and improved upon previous methods and devices, including hemocytometers. Automated equipment for counting blood cells was developed in the 1950s and 1960s.1
In the bloodstream, there are three types of cells: white blood cells (WBCs; leukocytes), red blood cells (RBCs; erythrocytes) and platelets (thromocytes). A CBC, one of the most routinely prescribed laboratory tests, reveals whether the numbers of WBCs, RBCs and platelets are abnormally high or low, and the totality of these values may facilitate the diagnosis of many types of disease. The Table summarizes the components of a CBC and provides the ranges of normal values for each.
Cellulitis of the hand
Cellulitis of the hand, thumb and finger are evaluated using a WBC count, ESR and CRP blood test. Elevation of the WBC count, ESR and or CRP levels are supportive but not conclusive evidence of infection.
Paronychia of the finger
Paronychia of the finger is evaluated using a WBC count, ESR and CRP blood test. Elevation of the WBC count, ESR and or CRP levels are supportive but not conclusive evidence of infection.
A felon of the finger is evaluated using a WBC count, ESR and CRP blood test. Elevation of the WBC count, ESR and or CRP levels are supportive but not conclusive evidence of infection.
In patients with rheumatoid arthritis (RA), CBC results typically show an elevated erythrocyte sedimentation rate (ESR), an indicator of inflammation. Other common tests evaluate blood samples for rheumatoid factor (RF; ~80% of RA patients) and citrulline antibodies (50–75%). Antinuclear antibody (ANA) and C-reactive protein (CRP) are also frequently detected in patients with RA. However, RF, ESR and CRP can be abnormal in other systemic autoimmune and inflammatory conditions, so these tests alone are not sufficient for a diagnosis of RA.
Extensor tendon rupture (Vaughn-Jackson Syndrome)
For extensor tendon ruptures secondary to RA, a blood test for RF can be used to support the RA diagnosis; tests evaluating ESR and CRP can help assess the severity of RA.