As early as the Middle Ages, conclusions were drawn about the causes of diseases by inspecting the blood ( generally obtained by bloodletting ) ( blood examination , hematoscopy ). Blood taken arterially , capillary or venously shows differences in color or brightness, depending on the punctured blood vessel, arterial blood is generally lighter than venous blood due to the oxygen-saturated hemoglobin . Any fatty vesicles or pathological coagulation on the blood taken provide indications of possible pathologies even before they are sent to the laboratory. On the basis of the laboratory results, the doctor can ultimately obtain important information about the health of his patient.
Simple values such as the blood cell count , which is often used in rheumatology, can also be determined on site in appropriate blood collection tubes without the aid of a laboratory. For the more specific blood values described in more detail below, an appropriately equipped laboratory is required and appropriately prepared tubes, e.g. B. with procoagulant substances in normal serum tubes or anticoagulant substances in EDTA or citrate tubes . Salts such as sodium fluoride can also be found in lactate plasma tubes. T. use.
Laboratory values can be used both in an acute emergency situation such as bleeding with a corresponding decrease in Hb or in the case of chronic diseases e.g. B. of rheumatic forms in the form of antibody diagnostics or tumor markers provide crucial (progress) diagnostic information and justify (emergency) therapies, both in practices, hospitals and during home visits or emergency calls by doctors with appropriate blood collection sets or automated rapid tests, e.g. B. on an increase in troponin in heart attack diagnosis or in blood sugar measurement . Rarer blood values often have to be determined in external laboratories, which means a longer period of time for the results to arrive and thus leaves an unclear, diagnostic window of time open which, if necessary, has to be closed by other parallel diagnostics depending on the disease.
Methods
Normal ranges
Normal ranges are typically assessed on a large number of apparently healthy individuals. The so-called normal values are given as the upper and lower limits of the range in which 95% of all measured values are located. A value outside the normal range does not automatically mean that the person in question is sick, on the contrary: every 20th value must, by definition, be outside the specified limits for healthy people.
Since the normal ranges also depend heavily on the methodology used, the population examined, etc., the limit values listed in this table are only to be understood as reference values. The normal values of the examining laboratory are relevant for the evaluation of laboratory results, and subsequently the medical interpretation of the measured values.
Reference ranges and decision limits
Conversely, all normal ranges overlap to a greater or lesser extent with the values that are obtained for patients. Your measured values depend e.g. B. on the type, stage, severity and treatment of the respective disease: The level of the tumor marker PSA z. B. definitely something about the overall size of the prostate, but next to nothing about the benign or malignant causes of a possible enlargement. In order to achieve an optimal separation between healthy and sick, you therefore need special reference ranges and decision limits for each medical question . For example, when testing a bank of blood , if you absolutely rule out HIV contamination, you will set the upper decision limit of the test extremely low (even at the risk that many probably harmless samples will have to be discarded), while for the same test with a Screening will set a comparatively higher limit value in order not to confront healthy people with false AIDS alarms.
^ Friedrich Lenhardt: Blood show. Studies on the development of hematoscopy. (Medical dissertation, Würzburg 1980) Pattensen with Hann. (now published by Königshausen & Neumann, Würzburg) 1986 (= Würzburg medical-historical research. Volume 22).
^ Friedrich Lenhardt: To the iconography of the blood show. In: Medical History Journal. Volume 17, Issue 1/2, 1982, pp. 63-77.
↑ See also Gundolf Keil : Eight parallels to the blood show texts of the Bremen Pharmacopoeia. Investigations into late medieval hematoscopy. In: Low German messages. Volume 25, 1969, pp. 17-135; and the same: To the Middle Low German blood show. ibid. Volume 26, 1970, pp. 125-128.
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