MEDICINE AND SURGERY "F"
Course of LABORATORY MEDICINE

Standard blood tests; tests of organ function

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      This lecture presents some elements of clinical reasoning on "standard" blood tests. It is meant to illustrate two common conditions: preventive screening of an asymptomatic person, and the initial study of a patient whose clinical picture is relatively aspecific. A standard blood test is indicated in every patient; but of course if a patient presents strongly indicative symptoms and signs, e.g. obvious jaundice or the symptoms of congenital erythropoietic porphyria (do you remember them? if not go to the lecture on porphyrias!), you will also prescribe much more specific analyses.

      It is very common for the physician to prescribe a routine selection of "standard" blood tests, e.g. during general screening or as an instrument of preventive medicine aimed at the early diagnosis of yet asymptomatic conditions (secondary prevention).
      It is also common that a patient may present with aspecific symptoms: fever, fatigue, mild dispnoea, imprecisely localized pain, mental confusion or somnolence, etc. These symptoms offer a poor guide to diagnosis, and you may be uncertain on the analyses to prescribe. Some routine analyses may help you to better focus the clinical case.

Audio: reasons to run a standard blood test

      In both the above cases a systematic approach to cinical reasonining is advisable, and may provide an important guide. To approach an aspecifically symptomatic patient, or an asymptomatic person, you will first record the anamnesis and carry out a physical examination; take the blood pressure; check for neurological symptoms and signs.
      Next, you can imagine your path as a sequence of questions. The first question you ask yourself is: is the patient condition acute or chronic? Is he/she an emergency or at risk to become an emergency? Medical emergencies usually give precise and important symptoms, thus they do not fall in the case we are presently discussing, and have their own specialistic approach. However there are conditions which, though not being actual emergencies, are at risk to become emergencies in a short time: e.g. a mild appendicitis may aggravate and cause a peritonitis in a few hours; a diabetic ketoacidosis may present itself as a mild confusional state and turn to ketoacidosis coma quite rapidly. Emergencies require the stabilization of the patient and the critcal decision on whether they require medical or surgical interventions, but we are not dealing with them here, as they are treated in dedicated courses.
      If the answer of your first question is negative (i.e. the patient is not a medical or surgical urgency that requires prompt hospitalization) you run a standard blood test. Standard blood tests may vary somewhat; however they usually include the blood cell count (the quantitation of red cells, of the various types of white cells and of platelets; hemoglobin concentration), total protein concentration, electrophoretic protidogram, glycemia, azotemia (BUN), creatininemia, transaminases (sGOT, sGPT), bilirubinemia, cholestrolemia, triglyceridemia, electrolythemia, and possibly other analyses. The general relevance of these routine tests is listed in the Table below.
 
Measurement Usual range Increases in Decreases in
Complete Blood Count (hemocytometer test)
Red blood cells 4.5-6 M/mmc Primary or secondary polycytemia; increased erythropoietin stimuls because of kidney or lung disease; high O2 affinity hemoglobinopathies Anemias, acute and chronic hemorrages
Hemoglobin 13-17 g/dL see above (polycytemias) Anemias, acute and chronic hemorrages, iron deficiency, vitamin deficiency, thalassemias, etc.
Platelets 150-400 K/mmc uncommon Damage of the bone marrow (e.g. leukemias, lymphomas, idiopathic medullary aplasia)
White cells (total) 4-10 K/mmc Leukemias Damage of the bone marrow (e.g. leukemias, lymphomas, idiopathic medullary aplasia)
White cells formula
Neutrophyle granulocytes 2-8 K/mmc (35-80%) acute bacterial infections; myeloid leukemias bone marrow aplasia; cancer; chemotherapy; autoimmune diseases
Eosinophyle granulocytes 0-800/mmc (0-7%) allergy; parasitic infection  
Basophyle granulocytes 0-200/mmc (0-2.5%) (myeloid leukemias)  
Lymphocytes 1-5 K/mmc (10-50%) (Lymphatic leukemias) (bone marrow aplasia; cancer; some types of infection; autoimmune diseases)
Monocytes 160-1000/mmc (0-12%) (chronic infections; autoimmune diseases) some types of infection; marrow aplasia; glucocorticoid therapy
 
Hematochemical tests
Glycemia 65-110 mg/dL Diabetes mellitus (type I; type II); Cushing syndrome insulinoma; excess insulin therapy in diabetic patients; Addison's disease; some glycogenoses
Azotemia (BUN) 10-50 mg/dL any kidney disease causing renal insufficiency Late stages of liver failure; inherited defects of the urea cycle
Creatininemia 0.6-1.3 mg/dL any kidney disease causing renal insufficiency  
Bilirubinemia total 0.3-1 mg/dL (conjugated 0.1-0.3 mg/dL) jaundice; liver disease (increase of unconjugated bilirubin only: hemolytic crisis)  
sGOT < 37 U/L Hepatitis; biliary obstruction; diseases causing the death of liver cells  
sGPT < 55 U/L Hepatitis; biliary obstruction; diseases causing the death of liver cells  
cholesterol total <200 mg/dL Hypercholesterolemia of dietary or genetic origin Mevalonic aciduria or other defect of cholesterol biosynthesis
Protidemia total 6-8 g/dL Often due to the gamma globulin fraction (see electrophoresis) decreased biosynthesis because of malnutrition or liver insufficiency; accelerated loss because of severe burn or nephrotic syndrome
Protein fractionation by electrophoresis
Albumin 55-65% (decrease of other components?) malnutrition, liver insufficiency, nephrotic syndrome, severe burn
Alpha 1 globulins 3-5%    
Alpha 2 globulins 7-12%    
Beta 1 globulins 4.5-7%    
Beta 2 globulins 3-6%    
gamma globulins 11-19% Bacterial infections; multiple myeloma (monoclonal peak) Congenital and acquired immunodeficiencies
 
Inflammation markers
Erythrocyte sedimentation rate (ESR) 2 mm/hour inflammation, bacterial infection uncommon
C-reactive protein < 8 mg/L inflammation, bacterial infection uncommon
 
Electrolytes
Sodium 135 mEq/L hyperaldosteronism  
Potassium 4-5 mEq/L   sweating; hyperaldosteronism
Calcium 4-5 mEq/L (2-2.5 mM) hyperparathyroidism; hypervitaminosis D; milk-alkali syndrome Chronic renal insufficiency; hypoparathyroidism
Chloride 100 mEq/L loss of bicarbonate (catution: chloride may be normal and bicarbonate may be decreased if other acids are present, e.g. in ketoacidosis) - run hemogas analysis increase of bicarbonate (e.g. chronic respiratory acidosis) - run hemogas analysis


Audio: standard blood tests

 
      A very important complement to the study of organ pathology is provided by the determination of intracellular enzymes released in the blood plasma by the death of cells of the affected organ. This is because the enzymatic profile is organ-specific and identifies which organ is affected by disease. In the standard blood test only sGOT and sGPT are routinely measured, but testing some more is a good practice, because information on some organs would otherwise not be available. This subject has been considered in the lecture on plasma proteins, to which the student is referred for details. In a general screening usually six or seven enzymes are measured, as detailed in the Table below; these provide a gross indication of the organs that may be affected; in case of positive results, more enzymes can be tested (see the lecture on plasma proteins).

Principal enzymes that can be tested in routine screenings
  Heart Brain Prostate Placenta Intestine Bone Liver Kidney Pancreas Sarcoidosis Leukocytes
Creatine phosphokinase (CK, CPK) +++ +++                  
Aspartate transaminase (AST, GOT) ++ ++         +++        
Alanine transaminase (ALT, GPT)             +++        
Lactate dehydrogenase (LDH) ++                    
Alkaline phosphatase (ALP)       +++ +++ +++ +++ +++     +++
Acidic phosphatase (ACP)     +++                
γ Glutamyl transferase (γGT)             +++ +++      

Audio: blood enzymes and organ damage

EVALUATION OF THE STANDARD BLOOD TEST

      Your next step is to evaluate the blood test. Look first for correlations; then reason along two different lines: by function, and by organ. These lines of reasoning are aimed at suggesting not one but several diagnostic hypotheses, to be evaluated in subsequent analyses and tests.
      The possible diagnostic hypotheses suggested by the initial evaluation of the patient may or may not belong to the same nosographic category: don't be fooled by categories! For example hyerglycemias are usually due to endocrine disorders, e.g. diabetes, Cushing's disease, hyperthyroidism. Thus in the majority of cases hyperglycemias fit a single nosographic category. Hypoglycemias are less common and do not fit in a single nosographic category: two possible causes among many are Addison's disease (a endocrine disorder), and glycogenoses (inherited defects of metabolism).

Correlations: is there more than a single abnormal value? If so, the two or more abnormal values may depend on one and the same disease or do they point to the coexistence of two diseases? Multiple diseases are rare in young patients, frequent in the elderly. Examples of typical associations due to single diseases are: increased BUN and anemia (kidney insufficiency with reduced production of erythorpoietin); increased bilirubin and hypoprotidemia (liver failure); reduced erythrocytes and platelets with increased white cells (leukemias); etc.

Reason first on the patient's condition, by function and ethiopathogenesis: are there anomalies in his/her blood test? Which type of anomaly did you notice?
      - Metabolic? Metabolic defects may be genetic, inherited (usually in children); toxic; endocrine. Are there alterations of glycemia (diabetes), lipidemia, electrolytes, urine or blood osmolarity?
      - Infectious? Is there leukocytosis, altered white cell's formula, increase of gamma globulins in the electrophoresis, increase of acute phase proteins, increase of Erythrocyte Sedimentation Rate (ESR)? Consider Tbc, subacute viral infections (e.g. cytomegalovirus). Has the patient visited a country where an infectious or parasitic disease is endemic (e.g. schistosomiasis, malaria)?
      - Due to malabsorption or malnutrition? Are there signs of avitaminoses?
      - Due to a chronic or acute inflammatory disease (possibly autoimmune)? Crohn disease? Lupus? Rheumatoid arthritis? Are there markers of acute or chronic inflammation? Prescribe an analysis of autoantibodies.
      - Neoplastic? Look for tumor markers; scintigraphy; imaging methods (e.g. total body NMR). Leukemias and lymphomas usually cause severe alterations in the blood cell count and usually affect all the corpuscles (pancytopenia); selective decrease of just one type of corpuscles (e.g. erythrocytes or platelets) usually suggest a different diagnosis, even though in the early stage of a leukemia or lymphoma one cell type may be affected more than the others.

Reason next on patient's condition by organ (this mode of reasoning is not alternative to the preceding one; carry out both, and cross your results):
      - Might the disturbance be neurological? Peripheral or central? Of ischemic, metabolic, toxic, infectious origin? Is liquor analysis indicated? The standard blood test carries little information about brain function, except for the possible presence of brain enzymes.
      - Might the disturbance be of cardiac origin? Circulatory? Is hypertension present? Are there abnormalities in the electrolytes? Are the heart enzymes increased?
      - Lung? Lung is poorly tested in standard blood tests, and requires the hemogas analysis; however a saturimeter may rapidly measure O2 saturation. The main indirect information on lung function in the standard blood test is given by chloride. The clinical reasoning is as follows:
[Na+] + [K+] = [Cl-] + bicarbonate + anion gap
Thus:
bicarbonate + anion gap = [Na+] + [K+] - [Cl-]
Abnormal chloride, in the presence of normal or nearly normal sodium and potassium points to an abnormal bicarbonate or anion gap or both and strongly indicates that a hemogas analysis is necessary. Unfortunately, this indication is not exhaustive of lung function and acid-base equilibrium because several acidoses and alkaloses may be normochloremic (e.g. acute respiratory acidosis and alkalosis; metabolic acidoses in which an increased anion gap may compensate for a decreased bicarbonate).
      - Is the gastrointestinal system affected? Abdominal pain? Diarrhoea or stipsis? Malabsorption? Diarrhoea or vomiting may cause major alterations in the electrolytes.
      - Liver? Is bilirubin increased? Is the protidogram normal? Are liver enzymes increased?
      - Kidney? Are BUN, and creatinine elevated? Kidney insufficiency may be associated to either increased or decreased production of erythropoietin, and hence to increased or decreased red cell count, in the absence of abnormalities in the platelet and leukocyte count.
      - Pancreas? Pancreas enzymes, notably amylase, are indicative of chronic or acute pancreatitis; hyperglycemia may be due to tipe I diabetes.
      - Endocrine system? Often, an endocrine system dysfunction manifests itself via metabolic disturbances (see above), and/or electrolyte disturbances.
      - Bone marrow and erythropoiesis are well represented in the standard blood test: essentially any alteration in the cell count (erythrocytes, platelets, and leukocytes) reflects either a malfunctioning of the bone marrow or an increased cell loss. Leukemias, lymphomas, bone marrow aplasia usually cause a severe reduction of all blood corpuscles (pancytopenia), with the possible exception of the cell clone affected by the leukemia.

Audio: reasoning on organs and functions

      In a young subject usually think of a single disease, possibly acute; in an elderly subject think of multiple diseases, at least some of them chronic: e.g. atheroslerosis, with chronic ischemic damage of heart ad kidney, possibly coupled with COPD.

      Assessment of organ function
      If the standard blood test suggests that some alteration of organ function is present, you should pursue this line by specific tests. Indeed specific tests are essential to assess organ functions. Moreover, in many cases the physician may suspect a disease affecting a specific organ, but he may not have a clue on its cause, which is essential for diagnosis: e.g. jaundice suggests a defect in liver function, increased azotemia (Blood Urea Nitrogen, BUN) suggests a defect in kidney function, peripheral oedema suggests cardiac failure, etc. None of these considerations is a diagnosis: diagnosis is liver cirrhosis or acute viral hepatitis, not "liver dysfunction". Thus organ diagnosis is extremely important and helps focusing a more precise ethiological diagnosis. The following table summarizes tests and laboratory evaluations that have been dealt with elsewhere in the course. In some cases the same test may be applied to more than a single organ or system, and a differential diagnosis is required.
 
    Organ           typical presenting symptom(s)             functionality tests      
 
Liver jaundice; dark urine; itch serum bilirubin concentration; transaminases and other liver specific enzymes; virological tests (antibodies, antigens, viral RNA); liver biopsy
Lung and respiratory tree dispnoea; cyanosis; fatigue hemogas analysis; measurement of respiratory volumes; measurement of pulmonary blood flow
Kidney increased BUN; confusive state; hypertension BUN; glomerular filtration rate (creatinine clearance)
Heart perypheral oedema; dispnoea; altered blood pressure; altered pulse; thoracic pain; abnormal heart sounds determination of central venous pressure; determination of LDH, CPK and other typical heart enzymes; measurement of pulmonary blood flow; ECG; echography
Bone marrow anemia, pallor, fatigue, petechiae hemochromocytometric analysis; marrow biopsy


      Laboratory findings in some common pathological conditions
      Arterial hypertension
      In 80% of the cases arterial hypertension has no other objective finding than the increase of pressure itself, and laboratory findings are negative (idiopathic hypertension); however, given the risks associated to chronic hypertension, an effort to ascertain possible causes is justified. The laboratory investigation of arterial hypertension points in two directions: endocrine disturbances, and kidney disfunctions acting via the renin-angiotensin system. Hormones that affect the arterial pressure include adrenaline and noradrenaline (e.g. in pheochromocytoma), and glycocorticoids (e.g. in Cshing's syndrome). All these hormones can be measured, but their blood leves vary significantly in the course of the day and in response to stimuli. The increase of noradrenaline in pheochromocytoma occurs in irregular bursts, associated to hypertensive crises, and followed by increased elimination of noradrenaline metabolytes (e.g. vanillylmandelic acid) in the urine.
      Renin is an proteolytic enzyme produced and released in the blood by the glomerulus as a response to low arterial pressure. In some kidney diseases (e.g. aterosclerotic kidney disease, stenosis of the renal artery) either or both kidneys may produce renin in excess. Renin digest the liver-produced serum protein angiotensinogen, releasing and endecapeptide fragment (angiotensin I), further converted in the lung to angiotensin II. The angiotensins are powerful vasoconstrictors and cause an increase of the arterial pressure (and a depression of the microcirculation). Renin inhibitors, converting enzyme inhibitors, and angiotensin antagonists are all available and may be used as a therapy of idiopatic and/or kidney-derived hypertension. The clinical laboratory can measure the level of angiotensins in the blood and urine.

      Chronic kidney failure
      Is common in the elderly, usually because of ateroscelrotic kidney disease. The typical laboratory findings increased urea and creatinine. GFR is decreased. Anemia (due to reduced production of erythropoietin) and hypertension (due to excess production of renin) may be present.

      Chronic liver failure, cirrhosis
      Presents increased bilirubin with jaundice, elevated liver enzymes, in advanced stages hypoalbuminemia, and hyperammonemia (due to reduced production of urea).

      Anemias
      Reduced hemoglobin and erythrocyte count. Possibly associated with the reduction of other blood cells (platelets, leukocytes). Anemia is a generic term, not a diagnosis, and the finding of anemia at a routine blood test indicates further analyses. The student is referred to the lecture on anemias in this course.

      Thrombocytopenic purpura
      Reduced platelet count is associated to purpura and may be due to several causes: bone marrow fibrosis, leukemias and lymphomas, autoimmune or drug-induced platelet destruction, etc.

Further readings
MedLine Plus CBC blood test

Questions and exercises:
1) Relevant abnormalities in the standard blood test of a patient were: leukocytosis, with marked increase of neutrophyles; increased C-reactive protein and ESR. These results suggest:
bacterial infection
a metabolic disease, possibly inherited
liver dysfunction

2) A patient presents hyperglycemia and reduced bicarbonate concentration. You prescribe further analysis to diagnose (or exclude):
kidney dysfunction
type 1 diabetes mellitus with ketoacidosis
type 2 diabets mellitus possibly associated to a metabolic syndrome

3) Reduced red blood cells and platelets, increased inflammation markers, abnormal electrolytes warrant further investigation for:
hematological neoplasia (e.g. leukemia)
kidney failure
heart failure

4) BUN and creatinine are markers of:
liver function
heart function
kidney function

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Thank you Professor (lecture on bilirubin and jaundice).

The fourth recorded part, the one on hyper and hypoglycemias is not working.
Bellelli: I checked and in my computer it seems to work. Can you better specify
the problem you observe?

This Presentation (electrolytes and blood pH) feels longer than previous lectures
Bellelli: it is indeed. Some subjects require more information than others. I was
thinking of splitting it in two nest year.

Bellelli in response to a question raised by email: when we compare the blood pH
with the standard pH we do not mean to compare the "normal" blood pH (7.4)
with the standard pH. Rather we compare the actual blood pH of the patient, with
the pH of the same blood sample equilibrated under standard conditions.
Thus, if we say that standard pH is lower than pH we mean that equilibriation with
40 mmHg CO2 has caused absorption of CO2 and has lowered the pH with respect
to its value before equilibration.

(Lipoproteins) Is the production of leptin an indirect cause of type 2 diabetes since
it works as a stimulus to have more adipose tissue that produces hormones?
Bellelli: in a sense yes, sustained increase of leptin causes the hypothalamus to adapt
and to stop responding. Obesity ensues and this in turn may cause an increase in the
production of resistin and other insulin-suppressing protein hormones produced by the
adipose tissue. However, this is quite an indirect link, and most probably other factors
contribute as well.

(Urea cycle) what is the meaning of "dissimilatory pathway"?
Bellelli: a dissimilatory pathway is a catabolic pathway whose function is not to produce
energy, but to produce some terminal metabolyte that must be excreted. Dissimilatory
pathways are necessary for those metabolytes that cannot be excreted as such by the
kidney or the liver because they are toxic or poorly soluble. Examples of metabolytes
that require transformation before being eliminated are heme-bilirubin, ammonia,
sulfur and nitrogen oxides, etc.

Talking about IDDM linked neuropathy can be the C peptide absence considered a cause of it??
Bellelli: The C peptide released during the maturation of insulin, besides being an indicator
of the severity of diabetes, plays some incompletely understood physiological roles. For
example it has been hypothesized that it may play a role in the reparation of the
atherosclerotic damage of the small arteries. Thus said, I am not aware that it plays a direct
role in preventing diabetic polyneuropathy. Diabetic neuropathy has at least two causes: the
microvascular damage of the arteries of the nerve (the vasa nervorum), and a direct
effect of hyperglycemia and decreased and irregular insulin supply on the nerve metabolism.
Diabetic neuropathy is observed in both IDDM and NIDDM, and requires several years to
develop. Since the levels of the C peptide differ in IDDM and NIDDM, this would suggest
that the role of the C peptide in diabetic neuropathy is not a major one. If you do have
better information please share it on this site!

In acute intermitted porphyria and congenital erythropoietic porphyria why do the end product
of the affected enzymes accumulate instead of their substrate??
Bellelli: First of all, congratulations! This is an excellent question.
Remember that a condition is which the heme is not produced is lethal in the foetus; thus
the affected enzyme(s) must maintain some functionality for the patient
to be born and to come to medical attention. All known genetic defects of heme
biosynthesis derange but do not block this metabolic pathway.
Congenital Erythropoietc Porphyria (CEP) is a genetic defect of uroporphyrinogen
III cosynthase. This protein associates to uroporphyrinogen synthase (which is present
and functional in CEP) and guarantees that the appropriate uroporphyrinogen isomer is produced
(i.e. uroporphyrinogen III). In the absence of a functional uroporphyrinogen III
cosynthase other possible isomers of uroporphyrinogen are produced together with
uroporpyrinogen III, mostly uroporphyrinogen I. The isomers of uroporphyrinogen
that are produced differ because of the positions of propionate and acetate side chains,
and this in turn is due to the pseudo symmetric structure of porphobilinogen. Only
isomer III can be further used to produce protoporphyrin IX. Thus in the
case of CEP we observe accumulation of abnormal uroporphyrinogen derivatives, which, as
you correctly observed are the products of the enzymatic synthesis operated by
uroporphyrinogen synthase.
The case of Acute Intermittent Porphyria (AIP) is similar, although there may be variants
of this disease. What happens is that either the affected enzyme is a variant that does not
properly associate with uroporphyrinogen III cosynthase or presents active site mutations
that impair the proper alignement of the phoprphobilinogen substrates. In either case
abnormal isomers of uroporphyrinogen are produced, as in CEP.
Also remark that in both AIP and CEP we observe accumulation of the porphobilinogen
precursor: this is because the overall efficiency of the biosynthesis of uroporphyrinogens is
reduced. Thus: (i) less uroporphyrinogen is produced, and (ii) only a fraction of the
uroporphyrinogen that is produced is the correct isomer (uroporphyrinogen III).


is it possible to take gulonolactone oxidase to synthesize vitamin C
instead of vitamin C supplement?
Bellelli: no, this approach does not work. The main reason is that
the biosynthesis of vitamin C, as almost all other metabolic processes, occurs intracellularly.
If you administer the enzyme it will at most reach the extracellular fluid but will not be
transported inside the cells to any significant extent. Besides, there are other problems
in this type of therapy (e.g. the enzyme if administered orally, may be degraded by digestive
proteases; if administered parenterally, may cause the immune system to react against a
non-self protein). In theory one could think of a genetic modification of the inactive human
gene of gulonolactone oxidase, but the risk and cost of this intervention would not be
justified. In addition to these considerations, except for cases of shipwreckage or
other catastrophes, a proper diet or administration of tablets of vitamin C is effective,
risk-free and unexpensive, thus no alternative therapy is reasonable. However, I express my
congratulations for your search on the biosynthesis pathway of ascorbic acid.


Resorption and not reabsorption would lead to hypercalcemia ie bone matrix being broken down.
Bellelli: I am not sure to interpret your question correctly. Resorption indicates destruction of the bone matrix and release of calcium and
phosphate in the blood, thus it causes an increase of calcemia. Reabsorption usually means active transport of calcium from the renal tubuli to the blood, thus
it prevents calcium loss. It prevents hypocalcemia, and thus complement bone resorption. To avoid confusion it is better use the terms "bone resorption" and "
renal reabsorption of calcium". If you have a defect in renal reabsorption, parthyroid hormone will be released to maintain a normal calcium level by means of
bone resorption; the drawback is osteoporosis.



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