Laboratory Evaluations

Laboratory medicine, or clinical pathology as it is also called, is the field of science and medicine that tests and examines tissue samples from the human body relevant to the diagnosis, treatment, and prognosis of diseases. The studies and tests, performed in the areas of biochemistry, bacteriology, hematology, histology, cytology, and serology, are ordered by physicians and other health care providers.

This chapter discusses the examination of blood and its components, synovial fluid, and urine specimens. The first section deals with those tests commonly performed as part of the routine evaluation of outpatients or preoperative patients. The next section discusses the laboratory findings of specific diseases as relates to orthopaedic physicians, taking into account that some generalized diseases result in orthopaedic problems. The definitions are designed to be comprehensive. According to accreditation and regulation, reference ranges of laboratory values must be reported with each laboratory result.

Because reference values depend on the geographic area, patient population, test methodology, and laboratory standardization, such values are not considered useful when published in textbooks because they are likely to be misleading. Therefore reference values have been deleted and the initial statement or sentence in either section should be an adequate overview for those not concerned with the complete nature of the study.

Care should be exercised when using laboratory terminology, decimal points, significant figures in laboratory data, and other specific information. Forms are provided for most tests requested. Laboratory results should never be given over the telephone except in emergency situations. Laboratory requests may be emergency (stat), urgent, or routine.

A blood test may examine the quantity and type of cells, the concentration of chemicals in the serum, and (rarely) the chemical composition of the blood cell. For each laboratory test, the definition states what component of the blood is tested. Note that for a test on both cells and fluid of the blood, the phrase whole blood is used. The preferred unit of volume is the liter (L).

The last two sections give a list of laboratory abbreviations and annotation of units.

Routine Evaluations

Complete Blood Count

The complete blood count (CBC) is a series of whole-blood tests to determine the quantity and other characteristics of blood cells. Some physicians prefer only a hemoglobin, hematocrit, and white count. Most laboratories use automated instruments to provide all the parameters as a part of a standard report, and a limited study such as a hematocrit and hemoglobin (H&H) test is not cost-effective. The comprehensive CBC may include the following tests.

  • bone marrow biopsy: laboratory test performed on bone marrow from a medullary cavity, such as the posterior iliac crest, to determine by microscopic examination the adequacy and morphologic characteristics of hematopoietic cells.

  • hematocrit (HCV), packed cell volume (PCV): the proportion of the red cells in whole blood expressed as a percentage.

  • hematocrit and hemoglobin (H&H): determination of hematocrit and hemoglobin levels only.

  • hemoglobin (Hb, Hgb): the iron-carrying protein in the blood. Normal values depend on age and gender (g/dl).

  • mean corpuscular hemoglobin (MCH): the average amount of hemoglobin in each red cell (pg).

  • mean corpuscular hemoglobin concentration (MCHC): the average concentration of hemoglobin in the red cells (g Hb/dl red cells).

  • mean corpuscular volume (MCV): average volume of a red cell. May not be reliable if red cells are abnormal (i.e., sickle cell disease) (fl).

  • platelets (Plt): a blood test measuring the number of platelets (thrombocytes) per volume of whole blood. Platelet counts are routinely done by automated instruments. Platelets play an important role in hemostasis (× 109/L).

  • red blood count (RBC): the number of red cells per unit volume of whole blood (million cells/μl) (# cells × 1012/L).

  • white blood count (WBC): number of white blood cells per unit volume of whole blood (thousand cells/μl) (× 109/L).

    • differential WBC (diff): percentage of different white cell types: neutrophils (segmented [mature] and precursors [immature]), lymphocytes, monocytes, eosinophils, basophils, and occasionally other forms. With present laboratory technology, the differential count is usually performed automatically and may not indicate the maturity of the neutrophils. In the unusual cases in which segmented neutrophils must be distinguished from more immature forms, the test may be performed by microscopic examination of the stained blood smear (× 109/L).

Basic Chemistry Profiles

Many hospitals offer groups of chemistry tests (called profiles or panels ) because these tests are frequently ordered together (e.g., serum electrolytes, hepatitis panel, renal panel). The basic components of these panels are listed here.

  • alanine aminotransferase (ALT): enzyme present in several organs but generally used to assess liver disease (U/L); also called SGPT.

  • albumin: serum concentration of the major osmotically active component of the blood. May be decreased in acute or chronic inflammation, liver disease, severe burns, or fever (mg/dl).

  • alkaline phosphatase (ALP), serum: enzyme present in bone, liver, and other organs. Marked elevations over adult normal values may be seen in healthy adolescents (U/dl, U/L).

  • aspartate aminotransferase (AST): enzyme present in many organs, particularly muscle and liver. Increased values may indicate damage to the organ (U/L); also called SGOT.

  • blood urea nitrogen (BUN): a metabolic waste product usually cleared by the kidney. When increased, may indicate kidney disease (mg/dl).

  • calcium (Ca) and phosphorus (P): in general constitute the two main bone mineral ions. The blood levels of these two ions do not necessarily denote bone problems (mg/dl). Phosphorus is also called phosphate.

  • cholesterol: a steroid-based compound that has been associated with predisposition to coronary artery disease. The level of cholesterol depends on both genetic and dietary factors. Cholesterol is usually bound to a carrier lipoprotein, which comes in two primary densities: high and low. High-density lipoprotein (HDL) cholesterol appears to vary inversely with coronary artery disease—the higher the level, the lower the disease frequency. On the other hand, low-density lipoprotein (LDL) cholesterol appears to vary directly with coronary artery disease (mg/dl).

  • creatinine (Cr): a metabolic by-product usually cleared by the kidney. Increased levels may indicate kidney disease (mg/dl).

  • gamma-glutamyltransferase (gamma-GGT), gamma-glutamyltranspeptidase (GGTP): serum enzyme that is frequently increased in liver disease caused by obstruction of the bile duct(s) (U/L).

  • lactate dehydrogenase (LDH): enzyme present in many organs. Increased values may indicate liver disease, red blood cell destruction within blood vessels, or recent heart attack (within 24 to 36 hours) (U/L).

  • total bilirubin: a metabolic by-product of liver metabolism of hemoglobin. Usually an indicator of liver function (mg/dl).

  • total serum protein: concentration of all proteins in the serum (g/dl).

  • uric acid (UA): a metabolic by-product usually elevated in cases of chronic gout. Elevated levels of uric acid are not necessarily correlated with acute attacks of gout (mg/dl).

Urinalysis (UA; Routine and Microscopic [R&M])

The routine urinalysis includes a notation of the color turbidity (appearance); specific gravity (density with respect to that of water, which tells how concentrated the urine is); pH (acidity or alkalinity); and the presence or absence of glucose, protein, bilirubin, ketone bodies, urobilinogen, and occult blood. A microscopic examination may be done on the urinary sediment, and the material seen may be described as white cells, red cells, epithelial cells, and a variety of crystals and casts (microscopic debris usually from diseased kidneys). The quantity of cells and crystals is expressed in the number of observed objects per high-power field (HPF) of the microscope, whereas the quantity of casts is expressed in the number of observed objects per low-power field (LPF).

General Blood and Serum Tests

The general orthopaedic and related laboratory examinations and results found in this section are grouped according to similar disease processes, such as arthritis, infection, metabolic disturbances, and hematologic disorders, and also for assessment of spinal fluid and liver function.

However, these categories are not used as unit headings because the tests are often used to study a variety of problems, depending on the clinical circumstance. The orthopaedic laboratory workup may include any or all of the following.

  • acid phosphatase (AcP): a serum assay for acid phosphatase activity. Elevations are usually associated with disease of the prostate, particularly cancer. Prostate-specific antigen (PSA) may be increased in prostatic disease, particularly in prostatic cancer. High PSA values (> 20 ng/ml) have been shown to correlate with metastatic disease. The % free PSA also correlates with disease. In general, lower percentage free PSA correlates with higher risk of disease. Greater than 30% free PSA has a lower probability of prostate cancer. Serial PSA levels are of value in following patients with prostate cancer after surgery or radiation (ng/ml).

  • activated partial thromboplastin time (APTT, PTT): a test that measures the clotting factors in the in trinsic coagulation system. It is the test of choice in monitoring patients receiving heparin to retard blood clotting.

  • alanine aminotransferase (ALT): an enzyme present in several organs but generally used to assess liver disease (U/L).

  • alkaline phosphatase (ALP, alk PO4 tase): test to determine the level of this enzyme. The most common sources of high values are rapid growth or fracture healing. In any growth spurt the value may be as high as three times normal. Other bone disorders causing an increase in alkaline phosphatase include Paget disease, primary bone tumors, some metastatic diseases, and osteomalacia. Because elevations in alkaline phosphatase can result from liver disorders, two additional tests may be performed: (1) heating the enzyme will destroy it if it comes from the liver and (2) abnormally high values of serum gamma-glutamyl transpeptidase (gamma GT) and alanine aminotransferase (ALT) indicate liver disease. Isoenzymes of alkaline phosphatase can be measured by indicating the organ of origin (U/L).

  • anti-citric citrullinated peptide antibody (anti-CCP): a serologic test often used in tandem with rheumatoid factor in the diagnostic assessment for rheumatoid arthritis. This test is more specific for rheumatoid arthritis than rheumatoid factor.

  • anti–double-stranded (native) DNA: test for antibodies against the genetic chemical information in the cell. High values are highly suggestive of systemic lupus erythematosus (IU/ml).

  • antinuclear antibody (ANA): an immunologic screening test that reveals the presence of serum antibodies against cellular nuclear material (DNA); usually reported as positive or negative. Elevations of ANA, especially when accompanied by the peripheral rim pattern of fluorescence, are associated with lupus erythematosus. An ANA is frequently found in minority children and adults at lower titers (1:80–1:160).

  • antistreptolysin O titer (ASO): this test is done mostly on children with joint complaints who are suspected of having rheumatic fever. The most meaningful finding for this test is an increase in the values during the course of 1 week. Values greater than 100 IU/ml in children and greater than 200 IU/ml in adults are associated with strep throat infection.

  • blood gases: a measurement of the amount of oxygen (O2) and carbon dioxide (CO2) in the blood. The oxygen is usually presented with a percent saturation value, which is normally more than 90%. The pH (acidity) of the blood is simultaneously determined.

  • C-reactive protein (CRP): a plasma protein not affected by the presence of circulating hormones or antiinflammatory drugs. Good indicator of inflammation or trauma. Correlates well with ESR (see later), but elevations appear and disappear before changes in ESR (mg/L or μg/L).

  • creatinine: by-product of metabolism that is cleared by the kidney. A 2-hour creatinine clearance (Ccr) indicates how effectively the kidney is functioning as a blood filter (mg/dl).

  • creatine kinase (CK; creatine phosphokinase [CPK]): an enzyme contained in many organs, principally skeletal muscle, heart muscle, and brain. In muscle disorders, particularly muscular dystrophy, it is elevated. In cases of suspected acute myocardial infarction, isoenzyme determinations help distinguish the organ of origin of the elevated enzyme level (U/L).

  • D-dimer: a breakdown product of cross-linked fibrin, it is useful in the evaluation of disseminated intravascular coagulation, deep vein thrombosis, or pulmonary embolism. The upper limits of normal grow steadily after age 50.

  • erythrocyte sedimentation rate (sed. rate, sedimentation rate, ESR):

    • modified Westergren method: test performed on anticoagulated whole blood to determine the speed of settling of cells in 1 hour. Three stages of sedimentation occur: initial aggregation and rouleaux formation, quick settling, and packing. The test is nonspecific, similar to determination of temperature or pulse, and a normal value is perfectly consistent with many disease states. An increased sedimentation rate may indicate certain conditions, particularly inflammation. Therefore this test is often used in evaluating bone and joint infections and other inflammatory diseases (mm/hr).

  • fasting blood sugar (FBS): test done to detect diabetes. Blood sample must be obtained at least 12 hours after the last meal. In the past, a glucose tolerance test (GTT) was a 2- to 5-hour study of both the blood and urine obtained from a patient who had taken 75 g of sugar after fasting. The most efficient GTT is a fasting and 2-hour postprandial (after eating) blood glucose. If these values are sufficiently abnormal according to the expected values for that particular laboratory, diabetes mellitus can be diagnosed. Three different sets of criteria are available for interpreting the plasma glucose levels in the GTT. These include the National Diabetes Data Group (NDDG), the World Health Organization (WHO) criteria, and age-related expected values for glucose criteria. Those values are available on request from your laboratory. There is usually little value in performing a 3- to 5-hour GTT (mg/dl).

  • hemoglobin electrophoresis: a test to determine types of red cell hemoglobin. Abnormalities are present in sickle cell disease, thalassemia, and other red cell disorders. The results of this test are reported as normal or described by the specific abnormality.

  • human leukocyte antigen–B27 (HLA-B27): an antigen on the surface of cells frequently present in patients with ankylosing spondylitis.

  • international normalized ratio (INR): ratio of value of patient’s prothrombin time to the mean of normal raised to the power of the international standard index.

  • prothrombin time (pro time, PT): a test that measures the clotting factors in the ex trinsic coagulation system, commonly done to monitor patients taking blood thinners such as warfarin sodium (Coumadin).

  • reticulocyte count: a blood cell test to determine the erythropoietic activity, thereby helping in the classification of anemia. When observed under the microscope, only 1 of 100 red cells will normally take up a stain, indicating it is less than 24 hours old. Finding an increased number of reticulocytes means probable increased red blood cell production, usually in response to anemia. However, the percentage of reticulocytes is relative to the total red cell count, so that mathematical correction of the percent reticulocytes is necessary for proper interpretation. Some centers have moved to reporting absolute reticulocyte counts (reference range: 25,000 to 75,000 cells/μl or 25 to 75 × 109/L).

  • rheumatoid factor (RF): a serologic test to determine the presence of certain antibodies frequently seen in autoimmune diseases. The antibodies may be detected by several methods; some are more sensitive than others. The individual laboratory will interpret the importance of positive, negative, or numeric results.

  • salicylates: a test can be done on the blood to determine the specific levels of salicylates or on the urine as a screening test for the presence of aspirin. This can be done to follow the treatment of arthritis or in the event of an accidental overdose. Salicylate is also present in oil of wintergreen, which some people use topically for relief of muscle pain, so elevated levels do not always indicate aspirin therapy or overdose (μg/ml).

  • serum lead: in cases of lead poisoning, the serum can be tested for that element specifically. Because lead is a heavy metal, a heavy metal screening test is frequently used to determine the presence of lead poisoning. Elevated lead levels can also be indirectly tested for by measuring the free red cell protoporphyrin or zinc protoporphyrin levels (μg/dl).

  • serum protein electrophoresis (SPE, SPEP): a test to determine the presence and amount of particular types of serum proteins; used to detect multiple myeloma—a malignancy of the cells that produces immunoglobulin (Ig). A report of a high immunoglobulin or monoclonal pattern may indicate myeloma. An immunoelectrophoresis is a similar test that defines the heavy and light chain isotypes or monoclonal proteins.

  • triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH): measures of the levels of thyroid-active hormones and the pituitary hormone controlling thyroid function. There are various methods for determining these levels to help recognize hyperthyroidism and hypothyroidism. A caution in interpreting such values should be made in chronically ill patients (ng/dl, μg/dl, μU/ml).

  • troponin: screen for evidence of myocardial change or the evaluation of a myocardial infarction.

Serum and Urine Tests for Metabolic Disease

The following tests, as well as some urine excretion tests, are done to assess bone metabolism (i.e., bone formation and resorption). These tests are used most often for diagnosing and following therapeutic response in patients with osteoporosis, Paget disease, hyperparathyroidism, and other metabolic bone diseases. In Paget disease, patients can have either evidence of decreased bone formation or increased bone resorption. These studies are often ordered by an endocrinologist but are of interest to the orthopaedist.

Serum Tests for General Bone Turnover Markers

  • 25-hydroxyvitamin D, 25-hydroxycholecalciferol (25[OH]D): measurement of 25(OH)D, a liver metabolite of vitamin D, in the serum is a good index for determining vitamin D deficiency and intoxication and aids in diagnosis of patients with metabolic bone diseases. It is measured by radioimmunoassay or competition binding protein assay (ng/ml).

  • 1,25-dihydroxyvitamin D, 1,25-hydroxycholeca­lciferol 1,25(OH)2D: measurement of 1,25(OH)2D is used in the management of hypocalcemic and hypercalcemic disorders, specifically the bone diseases parathyroid gland disorders, renal failure, and sarcoidosis, and for therapeutic management of treatment. It is measured by radioreceptor assay (pg/ml).

  • calcitonin: serum calcitonin is most frequently used for the diagnosis and management of medullary thyroid carcinoma. It is measured by either radioimmunoassay or the concentration technique (pg/ml).

  • parathyroid hormone (PTH): measured in serum for evaluation and differentiation of disorders of calcium metabolism. Intact PTH is measured by either immunoradiometric or immunochemiluminescent assay (pg/dl, pmol/L).

  • serum calcium (Ca): measures serum calcium concentration. Serum calcium levels are increased in hyperparathyroidism, while there is a concurrent decrease in serum phosphorus (PO4). The phosphorus determination in parathyroid disease depends on renal function. Calcium and phosphorus levels are commonly measured as a screening measure. Many diseases affect the blood levels of these two chemicals (mg/dl).

Serum Tests for Bone Formation

  • bone specific alkaline phosphatase (BAP, BSAP): determined by alkaline phosphatase isoenzyme electrophoresis or enzyme-linked immunosorbent assay (ELISA); can be a useful marker for the rate of bone formation (or bone turnover). It is usually elevated in Paget disease, after menopause, in hyperparathyroidism, and in other conditions, and its determination can help monitor patients with these conditions who are treated with antiresorptive therapy (U/L, IU/L).

  • osteocalcin or bone Gla protein (OC, ON, BGP): a serum marker for assessment of bone formation; most abundant noncollagenous protein in bone, measured by radioimmunoassay or immunoradiometric assay (ng/ml).

  • procollagen propeptide: serum marker of osteoblast activity measured in two chemical forms: the carboxyterminal propeptide (c-PCP, PICP) and the aminoterminal propeptide (N-PCP).

Serum Tests for Bone Resorption

  • C-telopeptide (cross-links, CTx or CTX): enzyme-linked immunosorbent assay is used to measure Type I collagen degradation products in urine as a bone resorption marker. It is reported as cross-links nmol/mmol creatinine. It is used for research and approved for clinical applications such as to monitor effectiveness of different antiresorptive therapies. CTX can also be measured in the serum and must be evaluated in the fasting state.

  • free pyridinium cross-links: for bone resorption; these are the cross-links of Type I collagen, which constitutes 90% of the organic bone matrix. Pyridinoline (PYD) and deoxypyridinoline (Dpd, DPYD) are excreted in the urine and not affected by diet. Dpd is more specific for bone metabolism. It is a useful marker to monitor therapies for metabolic bone diseases.

  • N-telopeptide (NTx or NTX): quantitative measure of excretion of cross-linked N-telopeptides of Type I collagen (NTx) is done by ELISA as a resorption marker. NTx is reported as bone collagen equivalents or creatinine. Measurement of NTx is intended for use in predicting skeletal response to hormonal antiresorptive therapy in postmenopausal women and therapeutic monitoring of other antiresorptive therapies (ng/ml). NTX can also be measured in the serum and must be evaluated in the fasting state.

  • tartrate-resistant acid phosphatase (TRAP): a serum test to measure bone resorption and to determine the metabolic activity of osteoclasts; specific acid phosphatase seen from active metabolic osteoclastic activity.

Urine Chemical Tests

Some minerals and other chemicals measured in blood are also measured in urine. These include calcium, phosphorus, creatinine, and uric acid. The following are indicators of bone resorption, with the exception of the mucopolysaccharides, which are an index of proteoglycan metabolic abnormalities.

  • hydroxyproline (HYP): urine test that measures the degradation products of bone matrix; total fasting urinary hydroxyproline-creatinine ratio is used traditionally as a marker of bone resorption. It is markedly increased in Paget disease. It is used to monitor treatment with antiresorptive drugs.

  • mucopolysaccharides: test done on the urine to determine the excretion of abnormal amounts of specific mucopolysaccharides that are seen in diseases causing dwarfism, Hurler syndrome, mental retardation, and other congenital problems.

  • pyridinoline collagen cross-links (PYD) and pyridinium collagen cross-links (PYD): these two names refer to the same urine tests used to measure cross-linked fragments of collagen that result from bone degradation.

Bacteriologic Studies

  • acid-fast bacillus (AFB): refers to the bright red appearance of mycobacteria when stained by a special technique and observed under a microscope. A more efficient method involving fluorescence microscopy is presently used.

  • anaerobic culture: bacterial culture grown in the absence of oxygen (obligate anaerobes) or minimal free oxygen (facultative anaerobes). Certain organisms require this environment for growth in contrast to the standard aerobic cultures grown in the presence of normal oxygen. Anaerobic bacteria, like their aerobic counterparts, can be pathogenic or nonpathogenic.

  • colony count (CC): the placement of a known amount of urine on culture media; the report is usually given in number of bacterial colonies per milliliter of urine.

  • culture and sensitivity (C&S): bacteria from a wound, urine, blood, joint fluid, throat, or any other source are grown in tubes or on plates. The bacteria are identified by combinations of biochemical reactions that they can or cannot carry out. The results of bacterial cultures are usually listed by individual organism along with its antimicrobial sensitivity.

    • typical bacterial species reports: the following bacterial species are frequently encountered in laboratory studies; they are listed for spelling purposes, without definitions. The terms common flora and normal flora denote the presence of normal, nonpathogenic bacteria.

      • Acinetobacter baumannii

      • Escherichia coli (E. coli)

      • Klebsiella pneumoniae

      • Mycobacterium avium

      • Mycobacterium marinum

      • Mycobacterium tuberculosis

      • Neisseria gonorrhoeae (cause of gonorrhea)

      • Pseudomonas aeruginosa

      • Salmonella organisms

      • Staphylococcus aureus (Staph. aureus)

      • Streptococcus organisms

  • Common fungal organisms are:

    • Actinomyces

    • Aspergillus

    • Blastomyces

    • Candida

    • Coccidioides

    • Cryptococcus

    • Histoplasma

  • fluorescent treponemal antibody (FTA): a highly specific treponemal serologic test for syphilis; usually interpreted as positive or negative. Nontreponemal screening tests commonly used are the Venereal Disease Research Laboratory (VDRL) and rapid plasma reagin (RPR). These are essentially the same test, with VDRL used on cerebrospinal fluid (CSF) and RPR used on serum.

  • Gram stain: a general stain used on microscopic slide specimens to aid in seeing various organisms and estimating their numbers. Depending on their color after processing, they are described as gram-positive or gram-negative. This aids in the initial selection of antibiotics likely to be useful. Also, white blood cells should be noted in sputum and wound specimens to indicate whether one is dealing with colonization (if white cells are not present) or actual infection (if they are).

  • polymerase chain reaction (PCR): used as a rapid identification of RNA or DNA specific for certain genes. Useful for identification of infectious agents and tumor mutations.

Other Special Studies

  • cerebrospinal fluid (CSF): a study that includes the following:

    • protein: normally 45 mg/dl.

    • glucose: normally two-thirds that of the serum glucose; decreased in bacterial infections.

    • white blood cells: normally 0 to 3/mm3; when an increased number of cells are present, they are divided into polys and lymphs.

    • culture: some fluid is placed on a growth medium to see if any organisms are present; occasionally, a slide is made from a smear of the fluid and a Gram stain done directly to determine the presence of bacteria.

    • bacterial antigen assay: used predominantly on pediatric population for rapid screening of bacterial surface antigens.

    • Cryptococcus latex antigen test: a rapid latex agglutination test for the qualitative and semiquantitative detection of the capsular polysaccharide antigens of Cryptococcus neoformans.

  • flow cytometry: for evaluation of hematolymphoid tumors, blood lymphocytes, and stem cells. A stream of single-file tumor cells is passed by the path of a laser. This may help in the relative grading of the tumor cells. Also, after staining with certain antibodies that have been linked to fluorescent chemicals that are expressed by the cell. Examples are lymphocytes from patients with acquired immunodeficiency syndrome (AIDS) can be counted by flow cytometry to determine the concentration of helper T lymphocytes—an indication of response to therapy.

  • synovial fluid evaluation ( Table 5-1 ): evaluation of synovial fluid for the type and quantity of cells in the fluid. The normal white count of synovial fluid is considered to be less than 200 cells/μl or mm3. The leukocyte count is performed in a standard hemocytometer.

Dec 24, 2021 | Posted by in ORTHOPEDIC | Comments Off on Laboratory Evaluations

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