Finger-prick blood samples

COHb is quite stable and its concentration does not change over a long period (up to 6 months) if the blood sample is stored in the dark and under sterile conditions. Blood levels of COHb are not expected to exceed 5% at ambient levels of CO. IPCS (1999) focuses on methods which can accurately measure COHb below 10%. A method which simply requires finger-prick blood is convenient for mass screening and is described in detail by Commins and Lawther (1965) in this method, the sample is diluted in ammonia solution, which is divided into two parts from one of these, CO is displaced by oxygen and the COHb containing part is placed in the sample beam of a spectrophotometer so that the instra-ment records the difference between the absorbance of COHb and oxyhemoglobin. 

Measurement of liver and other tissue concentrations of NAD(P) gives a precise estimate of niacin nutritional status and seems to be the most sensitive indicator in experimental animals. Measurement of the whole blood concentration of NAD (P) may serve the same purpose there is a good correlation between blood and liver concentrations of nicotinamide nucleotides in experimental animals. The sensitivity of the method is such that reproducible determinations can be carried out on finger-prick samples of 200 /xL of blood (Bender etal., 1982). 

Any method of blood sampling (finger prick, venepuncture, venous line) is satisfactory. Anticoagulated specimens (heparin, EDTA, acid citrate) are more convenient, since separation of red cells and plasma permits diagnostic assays of glycosylated hemoglobin and glycosylated albumin to be performed on one blood sample. 

Blood samples are collected from finger pricks or earlobe pricks into capillaries and from venou.s blood into test lubes. Capillaries and test tubes should be heparinized (to prevent blood clotting) and dried (to prevent uncontrolled sample dilution). To prevent contamination of the samples by OPs and CMs during collection, the skin must be cleaned before sampling. 

A useful indicator of excessive lead effect is the presence of free erythrocytic porphyrin (FEP). It can be measured from a small quantity of blood obtained by finger-prick. For confirmatory evidence of excessive lead absorption or poisoning, urine estimation of coproporphyrin and amino laevulinic acid are helpful. Inorganic lead is best monitored by blood sampling and organic lead by urine sampling. 

The measurement of bone lead is the most definitive indicator but is quite difficult to assess and interpret. Consequently the blood lead level (BLL) is used as the principal indicator of exposure. It is usually expressed in micrograms per decilitre of blood and can be measured from finger prick samples as a first order screen or from drawn blood samples. 

Blood samples suitable for analysis can be drawn by syringe or vacutainer from the antecubital vein or collected in a capillary tube after pricking a finger or the heel (in the case of infants) with a lancet. Blood samples of 5-10 ml drawn by syringe from a vein are preferred to capillary samples, inasmuch as hemolysis is usually less of a problem, dilution of the blood with extracellular fluids is minimized, and analytical reproducibility is better because of the larger sample size. In either case, however, acceptable values for retinol can be obtained from blood samples as small as 0.1-0.2 ml. 

Diabetics often need to take blood samples several times a day to check their blood sugar levels. This involves pricking a finger and putting a drop of blood onto a detector. This is obviously very inconvenient, not to mention painful, so there are hopes that in future diabetics will be fitted with an embedded sensor which will continuously read their blood glucose level and send this wirelessly to an external receiver. 

Also, the following are valuable adjuncts in screening measurements of hemoglobin in finger prick samples of blood, testing of urine with pretreated tapes for sugar and ketone bodies, and examination for the presence of sediment in the urine. In adolescents, the stage of sexual development in relation to age may be determined by physicians or nurses, since maturation may be delayed in malnutrition. 

The majority of these home blood glucose monitoring tools rely on the invasive withdrawal of blood, typically from a pricked finger, followed by application of the sample to an amperometric enzymatic test strip allowing GOx to catalyse the oxidation of glucose to gluconic acid (see Scheme... 

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