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blood analysis

Katz index by G.Bertelli

Generality

The Katz index ( IK ) is a blood parameter related to the erythrocyte sedimentation rate ( ESR ).

The calculation of the Katz index is based on the determination of the ESR after one hour and two hours after the blood sample was taken (in practice: the reading value of the first hour is added to half of the second hour, so yes divide it all by two).

The Katz index helps to signal an ongoing inflammation . If it is high, this parameter may indicate the presence of infections, autoimmune diseases and neoplasms in the body.

The Katz index decreases, however, in the case of polycythemia and some forms of anemia.

ESR: short introduction

  • When the blood is made incoagulable, the red blood cells tend to settle, as they have a density higher than that of the plasma; this property is used for determining the erythrocyte sedimentation rate (or erythrocyte sedimentation rate, indicated with the abbreviation VES ).
  • The ESR is therefore an expression of the speed with which the erythrocytes, present in a certain quantity of blood, are deposited on the bottom of a special graduated test-tube and is established by reading up to what level the red blood cells are sedimented. The facing is expressed in millimeters of sediment produced in an hour.
  • The ESR is a non-specific inflammatory index (ie generic ). In fact, many pathological processes can determine an increase in the erythrocyte sedimentation rate: rheumatic diseases, inflammation, various types of infections, anemia, tumors, etc. For this reason, the ESR must be interpreted in the context of other targeted clinical investigations. In other words, the finding of a high value must not cause concern, if other parameters result in the norm.

What's this

The Katz index is the numerical expression of the red blood cell sedimentation rate measured after one hour and two hours after the blood sample was taken. In more practical terms, this hematological parameter is obtained by adding the value of the ESR read at the first hour with half the value at the second hour, then dividing the whole by two.

It should be noted that the Katz index is hardly used, as it was found that the sediment measurement after two hours does not provide further diagnostic information with respect to the ESR determined at the end of the first hour after the withdrawal.

What is meant by red blood cell sedimentation?

  • The erythrocyte sedimentation rate is essentially conditioned by the characteristics of the plasma (in particular its protein composition ) and by those of the red blood cells (shape, number, tendency to aggregate, etc.).
  • In blood, red blood cells tend to remain in suspension, separated from each other thanks to the negative membrane charge that hinders the formation of aggregates ( rouleaux ). Under normal conditions, the protein component of the plasma is such as to preserve the surface charge of the red blood cells.
  • On the contrary, when phlogistic processes are established, the increased blood concentration of proteins typical of inflammation (including fibrinogen and C-reactive protein) leads to a weakening of repellent forces . Red blood cells, therefore, tend to aggregate into rouleaux, which have a high tendency to precipitate . The coarser these clusters are, the faster the sedimentation is.

Why do you measure

The Katz index is a laboratory test that provides general information on the presence or absence of inflammation and indirectly measures the degree of this state in the body.

Note. Inflammation is a reaction of the immune system that can develop rapidly ( acute form; for example, after a trauma or during an infection) or continues over time ( chronic form; as happens in the presence of autoimmune diseases or certain tumors ).

Furthermore, the Katz index allows monitoring of the course of an already diagnosed disease.

When is it measured?

  • The Katz index is calculated to reveal the presence of an inflammation caused by one or more conditions or pathologies such as: infections, tumors or autoimmune diseases .
  • The Katz index is useful to support the diagnosis and monitor the course and therapeutic response of specific diseases, including:
    • Arthritis (transient forms);
    • Systemic vasculitis;
    • Rheumatoid arthritis;
    • Systemic lupus erythematosus (SLE).
  • Calculation of the Katz index may be indicated by the doctor when the patient has signs and symptoms that may be associated with inflammation, such as:
    • Headache;
    • Pain in the knees and shoulders;
    • Pelvic pain;
    • Anemia;
    • Poor appetite;
    • Unexplained weight loss;
    • Joint stiffness.

Laboratory tests associated with the Katz index

The Katz index is not a specific test: high results of this parameter indicate the presence of an inflammation, without indicating to the doctor the location of this process and what is caused.

In the classification of diseases with inflammatory pathogenesis, the Katz index is usually used in combination with the evaluation of:

  • C reactive protein (PCR);
  • Anti-nucleus antibodies (ANA);
  • Rheumatoid factor;
  • Fibrinogen;
  • Total metabolic panel;
  • Blood count with formula.

Normal values

For the calculation of the Katz index, the erythrocyte sedimentation rate is determined twice:

  • After an hour ( VES of the first hour );
  • After two hours ( second hour ESR ).

The value is considered normal when it is included in the following reference ranges:

  • Women : 4-15;
  • Men : 4-10;
  • Older people: less than 20.

Unlike the ESR, the Katz index is not expressed in mm.

Note : the reference interval of the exam can change according to age, sex and instrumentation used in the analysis laboratory. For this reason, it is preferable to consult the ranges listed directly on the report. It should also be remembered that the results of the analyzes must be assessed as a whole by the general practitioner who knows the patient's medical history.

Katz High Index - Causes

As anticipated, a high Katz index suggests the presence of an ongoing inflammation, even if it does not provide information on its nature. Consequently, the increase in the parameter is proportional to that of inflammation, but it is not necessarily related to the severity of the disease.

It should be noted, then, that the attenuation of negative erythrocyte charges, by means of the so-called phlogosis proteins, is not immediate, but takes a few days. Therefore, the normalization of the values ​​of the ESR and the Katz index is late (in other words, these parameters can be high if the inflammation is ongoing or when it has already healed).

Moderately high Katz index

The Katz index may be high in the following conditions:

  • Anemia;
  • Systemic lupus erythematosus;
  • Rheumatoid arthritis;
  • Endocarditis;
  • Kidney diseases;
  • Osteomyelitis;
  • Rheumatic fever;
  • Thyroid diseases;
  • Infections (including syphilis, tuberculosis and mononucleosis).

Very high Katz index

An excessive rise in the Katz index compared to the norm can be indicative of the presence of:

  • Systemic infections (septicemia);
  • Giant cell arteritis;
  • Multiple myeloma;
  • hyperfibrinogenemia;
  • macroglobulinemia;
  • Necrotized vasculitis;
  • Rheumatic polymyalgia.

Low Katz Index - Causes

The Katz index may be reduced under the following conditions:

  • Drepanocytic anemia;
  • Heart failure;
  • Polycythemia;
  • hyperviscosity;
  • hypofibrinogenaemia;
  • Malnutrition;
  • Low plasma protein level, secondary to liver damage;
  • Allergy;
  • Dehydration;
  • Some medications (including aspirin, cortisone and quinine).

How to measure it

For the analysis of the Katz index it is necessary to take a blood sample from a vein in the arm.

How to calculate the Katz index?

The calculation of the Katz index is based on the determination of the erythrocyte sedimentation rate after one hour and two hours after collection.

The ESR measures, in particular, on the time it takes for erythrocytes (red blood cells) to precipitate (sediment) into a blood sample placed in a long, narrow test tube of standard height.

The result is reported in millimeters of fluid (plasma) that are present in the upper portion of the tube after one hour. When a blood sample is placed in the test tube, the cells normally settle relatively flat, leaving the plasma clearer.

Red blood cells settle more quickly in the presence of an increased concentration of phlogosis proteins in the blood, in particular those called "acute phase" (such as the C reactive protein and fibrinogen).

The Katz index is obtained by adding to the reading value at the first hour half of the reading value at the second hour, then dividing the whole by two.

Formula to calculate the Katz index

IK = [ESR of the 1st hour + (ESR of the 2nd hour / 2)] / 2

Preparation

The patient can undergo blood sampling, useful for calculating the Katz index, after a fast of at least 3 hours. Usually, the drugs do not significantly affect the result, but it is always advisable to inform the doctor about an ongoing therapy.

Factors that influence the Katz index

In interpreting the Katz index, the following factors must be taken into consideration:

  • Aging . The Katz index may increase with age, even in healthy subjects.
  • Female sex . In women, the Katz index may be slightly higher than in men. Furthermore, menstruation and pregnancy can cause a temporary rise in the parameter.
  • Anemia . The ESR is inversely proportional to the hematocrit, so the Katz index is high in anemia conditions.
  • Shape and volume of red blood cells . The Katz index is affected by the presence of microcytes (red blood cells smaller than normal) in the blood sample, as they sediment more slowly; the parameter could thus be reduced. On the contrary, high values ​​can be found in the case of high MCV (macrocytes).
  • Drugs . Some medicines may increase the Katz index. These include dextran, methyldopa, oral contraceptives, procainamide penicillamine, theophylline and vitamin A.

Interpretation of Results

Variations of the Katz index can be had for different causes.

Being a non-specific inflammatory marker, the result of the Katz index must be compared to other clinical findings, the patient's symptoms and the results of other in-depth investigations. After evaluating the complete picture, the doctor will be able to confirm or discard the suspected diagnosis.

High Katz Index

An increase in the Katz index is an indicator of phlogosis, although without having a precise and specific meaning for diagnostic purposes. An increase in the parameter can be had, in fact, indifferently in the course of infectious diseases (acute, subacute or chronic), many hemopathies, liver diseases, myocardial infarction and malignant neoplasms.

Therefore, the Katz index can contribute to the diagnosis if associated with other tests, but above all provides a valid support during therapy.

  • High Katz index, without any symptom indicative of a specific pathology : usually, the Katz index does not provide enough information to make medical decisions. Furthermore, a normal result cannot exclude inflammation or other conditions. A slight to moderate rise in the Katz index, not attributable to particular diseases, should lead to a repeat test after a few months.
  • Moderately high Katz index : it is found during pregnancy or during an infection caused by bacteria (such as, for example, pharyngitis) or anemia, but also in old age.
  • Very high Katz index : it can be determined by an inflammatory state such as rheumatoid arthritis, liver disease, kidney failure, trauma and so on, up to suspect the presence of a tumor.

When a disease is monitored over time, the increase in the Katz index may indicate an increase in inflammation or a poor response to therapy; when the same parameter is normal or decreased it can mean that the treatment is appropriate.

Katz index Low

A low Katz index can be observed in those pathologies in which the normal sedimentation of red blood cells is inhibited, as in the case of: polycythemia, leukocytosis and some liver diseases. Even in diseases characterized by anomalies in the shape of red blood cells (such as in sickle-cell anemia, in which the red blood cells have a sickle shape) a low Katz index can be found.

A low Katz index is also found in the presence of allergies and dehydration.

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