Comparing the efficiency of four diagnostic concentration techniques performed on the same group of intestinal parasites

Peer review under responsibility of Alexandria University Faculty of Medicine.

Available online 24 November 2017

Figures & data

Table 1 Comparison of the performance of four diagnostic concentration techniques in stool specimens previously identified as positive or negative for the presence of intestinal parasites.

Technique	No. of samples tested			Total	Sensitivity (%)	NPV (%)	Kappa value (%)
	Result	Negative	Positive
	Positive	0	67	67	55.83	60.15	50.28
FEC^*	Negative	80	53	133
	Positive	0	86	86	71.67	70.17	66.92
FTC^**	Negative	80	34	114
	Positive	0	84	84	70.00	68.96	65.12
FAC^**	Negative	80	36	116
	Positive	0	68	68	56.67	60.61	51.13
FGC^*	Negative	80	52	132

FEC: formol-ether concentration, FTC: Formalin-tween concentration, FAC: Formalin-acetone concentration, FGC: Formalin-gasoline concentration, NPV: negative predictive value.

* Versus.

** P < .05.

Fig. 1 Bar graphs showing the recovery of helminth ova and protozoan cysts by the FAC, FTC, FGC and FEC procedures in stool specimens.

Table 2 Sensitivity and negative predictive value (NPV) of each concentration method for the diagnosis of intestinal helminth species ova and protozoan species cysts.

Intestinal parasite and test	No. of samples tested		Detection of parasites in Known positive samples by:
	Positive	Negative^#	FTC	FEC	FAC	FGC
Protozoa (cysts)	60	40	42	45	39	42
Sensitivity %	100	100	70.0	75.0	65.0	70.0
NPV %	100	100	69.0	72.7	65.6	69.0
Giardia lamblia	30	20	21	18	20	19
Sensitivity %	100	100	70.0	60.0	66.7	63.3
NPV %	100	100	69.0	62.5	66.7	64.5
Entamoeba coli	30	20	21	27^*	19^**	23
Sensitivity %	100	100	70.0	90.0	63.3	76.7
NPV %	100	100	69.0	86.9	64.5	74.1
Helminths (ova)	60	40	44†	22^‡	45^†	26‡
Sensitivity %	100	100	73.3	36.7	75.0	43.3
NPV %	100	100	71.4	51.3	72.7	54.1
Ascaris lumbricoides	30	20	17	13	20	16
Sensitivity %	100	100	56.7	43.3	66.7	53.3
NPV %	100	100	60.6	54.0	66.7	58.8
Hymenolepis nana)	30	20	27^†	9^‡	25†	10‡
Sensitivity %	100	100	90.0	30.0	83.3	33.3
NPV %	100	100	86.9	48.8	80.0	50.0

* Versus.

** P < .05.

† versus.

‡ P < .01.

# Total of stool specimens previously identified as negative for the presence of intestinal parasites were not positive in studied different procedures.

Table 3 Comparison of physical and chemical characteristics of diethyl ether, tween, acetone and gasoline.

Properties	Ether (diethyl)	Gasoline	Tween20	Acetone
Boiling point (°C)	34.5	38–204	>100	56.2
Flash point (°C)	−45	−42.8	>110	−9.4
Melting point (°C)	−116.2	Less than −60	−14	−94.3
Flammable limits, % in air	1.9–36.0	1.4–7.6	Not available	3–13
Explosive limits, % in air	1.7–48	1.3–6.0	Not available	2.6–12.8
Auto-ignition temperature (°C)	160–180	280–456	Not available	537
Solubility in water	Yes	No	Yes	Yes
Specific gravity	0.714	0.72–0.78	1.095–1.105	0.787
Relative cost (reagent grade)	More than 10	Less than 1	2	5
Access	Limited access or less easy	Easy access	Less easy	Less easy
Anaesthetic vapour formation	Yes	No	No	No
Safety precautions	Keep away from sources of ignition, oxidizers, iodine, cholorine. Use in verywell ventilated areas	Keep away from sources of ignition, peroxides, nitric acid and perchlorates. Use in well ventilated areas	Keep away from sources of ignition, oxidizer and heat. Use well ventilated areas and appropriate areas and protective gloves	Keep away from sources of ignition, chloroform, chromic acid, sulphuric acid, nitric acid and other oxidizers. Use well ventilated areas and protective gloves

Table 4 Two-way contingency table showing the number of identified positives and the agreement between the formalin-ether concentration (FEC) and each other concentration techniques for the diagnosis of G. lamblia, E. coli, A. lumbricoides, and H. nana in stool specimens.

Protozoa/helminths	Technique		Formalin-ether			McNemartest	K value (P)
			Positives	Negative	Total
	FTC	Positive	13	8	21	0.581	0.456 (0.001)
G. lamblia:		Negative	5	24	29
	FAC	Positive	13	7	20	0.774	0.492 (0.000)
		Negative	5	25	30
	FGC	Positive	14	5	19	1.000	0.614 (0.000)
		Negative	4	27	31
	FTC	Positive	19	2	21	0.109	0.605 (0.000)
E. coli:		Negative	8	21	29
	FAC	Positive	18	1	19	0.021	0.608 (0.000)
		Negative	9	22	31
	FGC	Positive	20	3	23	0.344	0.603 (0.000)
		Negative	7	20	27
	FTC	Positive	8	9	17	0.424	0.338 (0.015)
A. lumbricoides:		Negative	5	28	33
	FAC	Positive	11	9	20	0.065	0.513 (0.000)
		Negative	2	28	30
	FGC	Positive	7	9	16	0.607	0.275 (0.050)
		Negative	6	28	34
	FTC	Positive	8	19	27	0.001	0.239 (0.020)
H. nana:		Negative	1	22	23
	FAC	Positive	7	18	25	0.001	0.200 (0.066)
		Negative	2	23	25
	FGC	Positive	5	5	10	1.000	0.416 (0.003)
		Negative	4	36	40