Common Screening Tests

Let us tell you more about the common and specialized medical tests done in th laboratory. Most are used commonly in many specialties and in general practice.

Screening tests are used to try to detect a disease when there is little or no evidence that a person has the disease. For example, measuring cholesterol levels helps identify the risk of cardiovascular disease, but these tests are performed for people who have no symptoms of cardiovascular disease. To be useful, screening tests must be accurate, be relatively inexpensive, pose little risk, and cause little or no discomfort.

Every test has some risk. The risk may be only the need for further testing if the result is abnormal, or it may be the possibility of injury during the test. Doctors weigh the risk of a test against the usefulness of the information it will provide.

No test is completely accurate. Sometimes a test result is incorrectly abnormal in a person who doesn't have the disease (a false-positive result). Sometimes a test result is incorrectly normal in a person who has the disease (a false-negative result). Tests are rated in terms of their sensitivity (the probability that their results will be positive when a disease is present) and their specificity (the probability that their results will be negative when a disease is not present). A very sensitive test is unlikely to miss the disease in people who have it. However, it may falsely indicate disease in healthy people. A very specific test is unlikely to indicate disease in healthy people. However, it may miss the disease in some who have it. Problems with sensitivity and specificity can be largely overcome by using several different tests. For example, a person who tests positive for AIDS with a very sensitive test is retested with another more specific one.

Routine blood testing is often misleading and may cause unnecessary anxiety and expense. When automated analyzers such as the Sequential Multiple Analyzer (SMA) are used to perform several blood tests, false-positive results are very common. By chance alone, at least one false-positive result is expected in almost half the people having 12 tests (SMA-12) and in two thirds of those having 20 tests (SMA-20). Because a doctor can't be sure whether a result in a particular person is false or true, a person with an abnormal result may need to be retested or undergo other tests.

Normal test result values are expressed as a range, which is based on the average values in a healthy population; 95 percent of healthy people have values within this range. These values vary somewhat among laboratories.

Blood Tests / Test Reference Range
(conventional units*)
- Acidity (pH) 7.35-7.45
- Alcohol (ethanol) 0 mg/dL (more than 0.1 mg/dL usually indicates intoxication)
- Ammonia 15-50 ug of nitrogen/dL
- Amylase 53-123 units/L
- Ascorbic acid 0.4-1.5 mg/dL
- Bicarbonate (carbon dioxide content) 18-23 mEq/L
- Bilirubin Direct: up to 0.4 mg/dL Total: up to 1.0 mg/dL
- Blood volume 8.5-9.1% of body weight
- Calcium 8.5-10.5 mg/dL (slightly higher in children)
- Carbon dioxide pressure 35-45 mm Hg
- Carbon monoxide Less than 5% of total hemoglobin
- CD4 cell count 500-1500 cells/ uL
- Ceruloplasmin 15-60 mg/dL
- Chloride 98-106 mEq/L
- Copper Total: 70-150 ug/dL
- Creatine kinase (CK or CPK) Male: 38-174 units/L Female: 96-140 units/L
- Creatine kinase isoenzymes 5% MB or less
- Creatinine 0.6-1.2 mg/dL
- Erythrocyte sedimentation rate (ESR) Male: 1-13 mm/hr Female: 1-20 mm/hr
- Glucose Fasting: 70-110 mg/dL
- Hematocrit Male: 45-52% Female: 37-48%
- Hemoglobin Male: 13-18 gm/dL Female: 12-16 gm/dL
- Iron 60-160 ug/dL (higher in males)
- Iron-binding capacity 250-460 ug/dL
- Lactate (lactic acid) Venous: 4.5-19.8 mg/dL Arterial: 4.5-14.4 mg/dL
- Lactic dehydrogenase 50-150 units/L
- Lead 40 ug/dL or less (much lower in children)
- Lipase 10-150 units/L
- Lipids: Cholesterol Less than 225 mg/dL (for age 40-49 yr; increases with age)
- Triglycerides 40-200 mg/dL (higher in males)
- Liver function tests Include bilirubin (total), phosphatase (alkaline), protein (total and albumin), transaminases (alanine and aspartate), prothrombin
- Magnesium 1.5-2.0 mEq/L
- Mean corpuscular hemoglobin (MCH) 27-32 pg/cell
- Mean corpuscular hemoglobin concentration (MCHC) 32-36% hemoglobin/cell
- Mean corpuscular volume (MCV) 76-100 cu um
- Osmolality 280-296 mOsm/kg water
- Oxygen pressure 83-100 mm Hg
- Oxygen saturation (arterial) 96-100%
- Phosphatase (acid), prostatic 0-3 units/dL (Bodansky units)
- Phosphatase (alkaline) 50-160 units/L (higher in infants and adolescents)
- Phosphorus (inorganic) 3.0-4.5 mg/dL
- Platelet count 150,000-350,000/mL
- Potassium 3.5-5.0 mEq/L
- Prostate-specific antigen (PSA) 0-4 ng/mL (increases with age)
- Protein: Total 6.0-8.4 gm/dL Albumin 3.5-5.0 gm/dL Globulin 2.3-3.5 gm/dL
- Pyruvic acid 0.3-0.9 mg/dL
- Red blood cell (RBC) count 4.2-5.9 million/uL/cu mm

Sequential multiple analyzer (SMA): SMA-6 (6 tests) See individual tests: bicarbonate, chloride, glucose, potassium, sodium, urea nitrogen SMA-12 (12 tests) See individual tests: bicarbonate, calcium, chloride, cholesterol, creatinine, glucose, phosphatase (alkaline), potassium, sodium, transaminases (alanine and aspartate), urea nitrogen SMA-20 (20 tests) See individual tests: protein (albumin), bicarbonate, bilirubin (direct and total), calcium, chloride, cholesterol, creatinine, gamma-glutamyltransferase, glucose, lactic dehydrogenase, magnesium, phosphatase (alkaline), potassium, protein (total), sodium, transaminases (alanine and aspartate), urea nitrogen, uric acid
- Sodium 135-145 mEq/L
- Thyroid-stimulating hormone (TSH) 0.5-5.0 ?units/mL
- Transaminase: Alanine (ALT) 1-21 units/L Aspartate (AST) 7-27 units/L
- Urea nitrogen (BUN) 7-18 mg/dL
- Uric acid 3.0-7.0 mg/dL
- Vitamin A 30-65 ug/dL
- White blood cell (WBC) count 4,300-10,800 cells/uL/cu mm

*Conventional units can be converted to international units by using a conversion factor.