PROTEIN (TOTAL) - serum

PROTEIN (TOTAL) - serum

Application: Assessment of hydration, nutritional status, protein-losing disorders or liver disease.


Explanation: Albumin and globulin comprise most of the protein in the blood.  Albumin, which is manufactured in the liver, functions mostly to maintain intravascular osmotic pressure, and further serves to transport hormones, enzymes, etc.
   Globulin appears in several varieties: the Gamma globulins are the immune globulins (antibodies).  Alpha1 globulin and Alpha2 globulin include several important transport molecules, cholinesterase, and prothrombin.  Beta1 and Beta2 globulins include plasminogen, transferrin, complement, and fibrinogen.

   Serum globulin and albumin are indicators of nutrition. Undernourished patients have diminished serum protein levels, especially post-surgically. Decreased levels may also be associated with overhydration, chronic liver disease, protein losing disorders (eg nephrotic syndrome, protein-losing enteropathy), and fluid shifts into the extravascular space (e.g.- burns). Decreased levels may also be seen as part of an acute phase response. Dehydration is a cause of increased serum protein.
   Protein electrophoresis separates the various blood proteins into discrete zones, and several diseases can be associated with distinct electrophoretic patterns



Specimen: 5 ml blood in red-top tube.


Reference Interval:

Neonate:
4.0-7.5 g/dL
Child <2 years:
5.0-7.5 g/dL
Adult:
6.2-8.0 g/dL

Liver Function Tests

Liver Function Tests (LFT’s)

ALANINE AMINOTRANSFERASE (ALT) - serum
 Application: Detection and monitoring of liver cell damage.

 Explanation: This is an enzyme found largely in the liver. In liver disease, ALT is elevated in roughly the same circumstances as the AST but appears less sensitive, apparently requiring more extensive or severe acute hepatic damage to give abnormal values. ALT, therefore, is relatively specific for liver cell damage, unlike AST or LDH. In general, the ALT level usually returns to normal levels before the AST.

The AST/ALT ratio is typically >1 in alcoholic liver disease and <1 in non-alcoholic liver disease.


Specimen: 7 ml blood in red-top tube.


Reference Interval:
            4-36 U/L   (Adult/Child)
            elderly may be slightly higher
            infant may be twice as high

LACTATE DEHYDROGENASE (LD) - serum

LACTATE DEHYDROGENASE (LD) - serum

Application: Diagnosis of myocardial infarction , esp. >48 hours after onset of chest pain.


Explanation: LD becomes elevated 24-48 hrs post-infarction. It peaks between 48-72 hrs, and slowly falls to normal between 5-10 days. LD tends to parallel AST, at twice the time. LD is more sensitive than AST and is elevated  even in infarcts that show no AST abnormality. In acute liver damage LD is not as sensitive as AST. In the acutely and chronically passively congested liver, LD is most often normal or minimally elevated.

   LD is actually a group of enzymes. Individual enzymes or isoenzymes make up “total LD”. LDH-1 is found mainly in RBC, heart, and kidney, as is LDH-2. LDH-3 is in lung tissue, while LDH-5 is mainly in liver tissue. Skeletal muscle has significant representation in all fractions although higher in LDH-5. LD isoenzyme fractionation is a method of diagnosing myocardial infarction when liver damage is suspected to contribute to the total LD increase. For example, in liver damage without MI, LDH-1 is normal and most LD increase is due to fraction 5. If MI and liver damage coexist, fractions 1 & 5 are both elevated. Normally, LDH-2 is slightly more elevated than LDH-1. Classically, in a myocardial infarction LDH-1 is markedly elevated, more so than LDH-2; thus, there is inversion of the usual pattern, called "flip" isoenzyme pattern.

Specimen: 7-10 ml blood in red-top tube.


Reference Interval:
            100-190 U/L

Isoenzymes:
            LDH-1: 17-27%
            LDH-2: 27-37%
            LDH-3: 18-25%
            LDH-4: 3-8%
            LDH-5: 0-5%
           

ANION GAP - serum

ANION GAP - serum
Application: Investigation of metabolic acidosis.

 
Explanation: Since serum is electrically neutral, total anions and total cations must be equal. Na+ and K+ are the major reported cations. Cl- and HCO3- are the major reported anions. The totals of anion and cations in serum are not equal. The sum of unreported cations, such as, Ca++ and Mg++ average 7 mEq/L, and the sum of unmeasured anions (proteins, phosphate, sulfates, organic acids), average 24 mEq/L. So, normally, there exists a net excess of about 17 mEq/L of unmeasured anions in serum. When the total Cl- and total CO2 concentrations are added together and subtracted from the Na+ and K+ concentrations, the difference should be less than or equal to 17 mEq/L. If the anion gap exceeds 17 mEq/L, it indicates an increase in one or more of the unmeasured anions.

            Anion gap = (Na + K) - (Cl + HCO3).

   Causes for increased anion gap are: metabolic acidosis (e.g.- lactic acidosis), uremia, ketotic states, toxin ingestion, such as methanol or salicylates. Metabolic acidosis with a normal anion gap is seen in renal tubular acidosis and in other causes of bicarbonate loss (e.g.- diarrhea).

 Specimen: 5 ml blood in red-top tube.

 
Reference Interval:
            8-16 mEq/L

OSMOLALITY - serum

OSMOLALITY - serum
Application: Suspected poisoning with alcohol, methanol, ethylene glycol, acetone, isopropanol, diethyl ether or paraldehyde. Assessment of water and electrolyte balance, in conjunction with urine osmolality.


Explanation: Osmolality measures the concentration of dissolved particles in blood. Osmolality increases with dehydration and decreases with overhydration. An increased osmolar gap indicates the presence of alcohol or other osmotically active substances (organic acids, sugars).  In the presence of these substances, there is an “osmolal gap”.  This gap represents the difference between what the serum osmolality should be (based on serum Na, glucose, and BUN) and what the osmolality is actually measured to be.  A large gap should raise suspicion of the presence of organic acids (e.g.-ketones) excessive glucose, or ethanol byproducts. Urine osmolality measurements may assist interpretation.

 Specimen: 5 ml blood in red-top tube.

Reference Interval:
285-295 mOsm/kg H2O   (Adult)
275-290 mOsm/kg H2O   (Child)