Basic Laboratory Medicine

Question 1

WBC Count

Answer 1

• Normal range 4.0 -10 mm3
• Elevated WBC counts: generally indicate moderate to severe bacterial infections. As an example, a simple infected cut on a finger will not raise the WBC significantly (i.e. out of the normal range). If the infection progresses and becomes severe, WBC counts will rise. We take elevated WBC counts very seriously and aggressive treatment with antibiotics / surgery is indicated
• Depressed WBC counts: Suppression of the bone marrow (WBC’s made here) for any number of causes may result in depressed WBC counts. Example: HIV/AIDS; chemotherapy; toxins; overwhelming sepsis (infections involving the blood stream infections); certain viral infections
• WBC differential: The WBC count may be broken down into subcategories of the various types of WBC’s. This is reported as percent of each type of WBC and is very helpful in the clinical setting to make judgments regarding infection.

Question 2

Hematocrit

Answer 2

• Normal 36-45 % (roughly 3 times Hgb)
• Similar, but not the same as Hgb. Ease of performance makes this popular in office labs. Basically a volume of blood is collected and the sample is “spun down” so all the RBC’s are at one end of the collection tube. A calculation is done: volume of the packed RBC’s / total volume of contents of tube X 100 gives a % Hct . It measures the proportion of RBC’s which is accurate and useful if all RBC’s contain a normal amount of Hgb. In other cases, we need more sophisticated information to arrive at a correct diagnosis. For example: if an individual has smaller than normal RBC’s(microcytic ), the Hct may be low, but the Hgb is normal. If the individual has larger than normal RBC (macrocytic), Hct may be normal, but Hgb low

Question 3

Hemoglobin

Answer 3

• Normal 12.5 – 16 g/dl
• Hgb is a measurement of the molecules which carry 02 which under normal circumstances, are contained within the RBC’s
• Elevated Hgb levels may result from several conditions. Chronic hypoxia (ex. living at altitude; COPD) will raise Hgb levels. ; bone marrow abnormalities resulting in production of too many RBC’s (polycythemia) will result in elevated Hgb levels. Hgb may also rise in a contracted blood volume states (dehydration – more RBC/mm3 of blood even in the face of the correct number of total RBC’s)
• Low Hgb /HCT may result from one of three events:
• Not making Hgb: varied causes and degrees of bone marrow failure to meet needs (ex. iron deficient anemia; bone marrow failure)
• Losing Hgb: bleeding seen and unseen – (ex. hemorrhage; occult GI bleeding, menometrorrhagia [very heavy and prolonged periods] )
• Using Hgb up: typically a hemolytic process where RBC’s are chewed up by abnormal immune mechanisms

Question 4

Platelets

Answer 4

• Normal range: 150,000 -400, 000/mm3
• Adequate platelet numbers are essential for clotting. Conversely elevated platelets counts may result in unwanted thrombosis (clots) resulting in stroke, myocardial infarction, etc.
• High platelet counts occur in many conditions: bone marrow abnormalities; iron deficient anemias (as a response to the anemia); infections, others
• Low platelets counts may result from many, many causes. Examples include decreased production: marrow failure; sepsis; increased destruction: abnormal immune mechanisms destroying platelets; Using platelets up: Disseminated intravascular clotting (DIC)

Question 5

The Basic Metabolic Profile

Answer 5

(aka. BMP; Chem 7; SMA 6/7)
Very commonly ordered series of tests
• Serum electrolytes include
- Sodium (Na+) normal 134-146 mEq/l
- Potassium (K+) normal 3.4 -5 mEq/l
- Chloride (Cl-) normal 97-110 mEq/l
- Carbon dioxide (dissolved as HCO3- / bicarbonate) normal 18-28 mEq/l
• Serum Glucose normal 60-100 mg/dl (fasting state)
• Renal Function tests (adequate GFR)
- Serum Creatinine (Cr): normal .8-1.4 mg/dl
- BUN (Blood Urea Nitrogen) 8-25 mg/dl

Question 6

The Comprehensive Metabolic Profile (aka. CMP)

Answer 6

A very commonly ordered test which includes the basic metabolic profile measurements plus several others. In a certain sense it is a smattering of tests of various organ systems. Reports typically are generated for 14 tests although there is some variation in the number of tests depending on the sophistication of the machine doing the tests. Older names include SMA 12, SMA 20; SMAC.

Question 7

The Comprehensive Metabolic Profile (aka. CMP)

Answer 7

• Serum electrolytes include
- Sodium (Na+) normal 134-146 mEq/l
- Potassium (K+) normal 3.4 -5 mEq/l
- Chloride (Cl-) normal 97-110 mEq/l
- Carbon dioxide (dissolved as HCO3- / bicarbonate) normal 18-28 mEq/l
- Calcium (Ca++) 8.7 -10.2 mg/dl
• Liver Panel - How well is the liver doing its job
- Total protein 6 - 8.5 g/dl
- Albumin 3.5 – 5.5 g/dl
- Globulin 1.5 – 4.5 (immune system too)
• Is there liver inflammation (ex. hepatitis, tumor, bile blockage, alcohol etc.)
- AST (Aspartate Aminotransferase ) 0-40 iu/l
- ALT (Alanine Aminotransferase ) 0- 55 iu/l
- Bilirubin 0.0- 1.2 mg/dl (hemopoetic system too!)
- Alkaline phosphatase 25-150 iu/l (bone too!)
• Renal Function
-Creatinine
-BUN
• Glucose 60-100 mg/dl (fasting state)

Question 8

Urinalysis

Answer 8

•	Specific Gravity – S.G. range roughly from 1035 (extremely 				concentrated urine) to 1001 (extremely dilute urine). A SG of 1010 is 	roughly isotonic with normal serum osmolarity (295 mOsm/l)
•	pH ranges 5-9; highly diet dependent
•	Abnormal constituents:
			A. Glucose
			B. Proteinuria
			C. Hematuria
			D. Presence of WBC, RBC’s
			E. Large numbers of crystals
			F.  Casts (“casts” are substances formed into the shape of the renal tubules as if they had been poured into a mold)
			G. Bilirubin